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ction on each element of the input list.
=== ML ===
ML (1973) stands for "Meta Language." ML is statically typed, and function arguments and return types may be annotated.
ML is not as bracket-centric as Lisp, and instead uses a wider variety of syntax to codify the relationship between code elements, rather than appealing to list ordering and nesting to express everything. The following is an application of times_10:
times_10 2
It returns "20 : int", that is, 20, a value of type int.
Like Lisp, ML is tailored to process lists, though all elements of a list must be the same type.
=== Prolog ===
Prolog (1972) stands for "PROgramming in LOGic." It was developed for natural language question answering, using SL resolution both to deduce answers to queries and to parse and generate natural language sentences.
The building blocks of a Prolog program are facts and rules. Here is a simple example:
Given this program, the query eat(tom,jerry) succeeds, while eat(jerry,tom) fails. Mor
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m,jerry) succeeds, while eat(jerry,tom) fails. Moreover, the query eat(X,jerry) succeeds with the answer substitution X=tom.
Prolog executes programs top-down, using SLD resolution to reason backwards, reducing goals to subgoals. In this example, it uses the last rule of the program to reduce the goal of answering the query eat(X,jerry) to the subgoals of first finding an X such that big(X) holds and then of showing that small(jerry) holds. It repeatedly uses rules to further reduce subgoals to other subgoals, until it eventually succeeds in unifying all subgoals with facts in the program. This backward reasoning, goal-reduction strategy treats rules in logic programs as procedures, and makes Prolog both a declarative and procedural programming language.
The broad range of Prolog applications is highlighted in the Year of Prolog Book, celebrating the 50 year anniversary of Prolog.
=== Datalog ===
The origins of Datalog date back to the beginning of logic programming, but it was ident
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e beginning of logic programming, but it was identified as a separate area around 1977. Syntactically and semantically, it is a subset of Prolog. But because it does not have compound terms, it is not Turing-complete.
Most Datalog systems execute programs bottom-up, using rules to reason forwards, deriving new facts from existing facts, and terminating when there are no new facts that can be derived, or when the derived facts unify with the query. In the above example, a typical Datalog system would first derive the new facts:
Using these facts, it would then derive the additional fact:
It would then terminate, both because no new, additional facts can be derived, and because the newly derived fact unifies with the query
Datalog has been applied to such problems as data integration, information extraction, networking, security, cloud computing and machine learning.
=== Answer Set Programming ===
Answer set programming (ASP) evolved in the late 1990s, based on the stable model (ans
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in the late 1990s, based on the stable model (answer set) semantics of logic programming. Like Datalog, it is a subset of Prolog; and, because it does not have compound terms, it is not Turing-complete.
Most implementations of ASP execute a program by first "grounding" the program, replacing all variables in rules by constants in all possible ways, and then using a propositional SAT solver, such as the DPLL algorithm to generate one or more models of the program.
Its applications are oriented towards solving difficult search problems and knowledge representation.
== See also ==
Inductive programming
List of declarative programming languages
== References ==
== External links ==
Frans Coenen. Characteristics of declarative programming languages. 1999.
Robert Harper.
What, If Anything, Is A Declarative Language?. 2013.
"There Is Such A Thing As A Declarative Language, and It's The World's Best DSL". 2013.
Olof Torgersson. A Note on Declarative Programming Paradigms and the Future
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Declarative Programming Paradigms and the Future of Definitional Programming. 1996.
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Broadcast programming is the practice of organizing or ordering (scheduling) of broadcast media shows, typically radio and television, in a daily, weekly, monthly, quarterly, or season-long schedule.
Modern broadcasters use broadcast automation to regularly change the scheduling of their shows to build an audience for a new show, retain that audience, or compete with other broadcasters' shows. Most broadcast television shows are presented weekly in prime time or daily in other dayparts, though there are many exceptions.
At a micro level, scheduling is the minute planning of the transmission; what to broadcast and when, ensuring an adequate or maximum utilization of airtime. Television scheduling strategies are employed to give shows the best possible chance of attracting and retaining an audience. They are used to deliver shows to audiences when they are most likely to want to watch them and deliver audiences to advertisers in the composition that makes their advertising most likely to
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sition that makes their advertising most likely to be effective.
With the growth of digital platforms and services allowing non-linear, on-demand access to television content, this approach to broadcasting has since been referred to using the retronym linear (such as linear television and linear channels).
== History ==
With the beginning of scheduled television in 1936, television programming was initially only concerned with filling a few hours each evening – the hours now known as prime time. Over time, though, television began to be seen during the daytime and late at night, as well on the weekends. As air time increased, so did the demand for new material. With the exception of sports television, variety shows became much more important in prime time.
== Scheduling strategies ==
=== Lead-ins and lead-outs ===
Broadcasters may schedule a program to air before or after a widely viewed tent-pole program, such as a popular series, or a special such as a high-profile sporting eve
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, or a special such as a high-profile sporting event (such as, in the United States, the Super Bowl), in the hope that audience flow will encourage the audience to tune-in early or stay for the second program. The second program is usually one that the broadcaster wants to promote to a wider audience, such as a new or lower-profile series. Sometimes, a lower-profile program may be scheduled between two tentpole programs, a technique known as hammocking.
Lead-outs can sometimes help to launch new programs and talent; in 1982, NBC premiered Late Night with David Letterman as a lead-out for its long-running late-night talk show The Tonight Show Starring Johnny Carson. Characterized by an off-beat style appealing to young adults, Late Night helped launch the career of host David Letterman, and influence later entries into the genre. Despite Carson's endorsement of Letterman as a successor following his 1992 retirement, NBC chose Jay Leno instead, and Letterman departed for CBS to host a sp
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stead, and Letterman departed for CBS to host a spiritual successor—Late Show with David Letterman—beginning in the 1993–94 season. Late Night would continue as a franchise with hosts such as Conan O'Brien and Jimmy Fallon—both of whom would later go on to host The Tonight Show.
The same season, Fox scheduled The X-Files as a lead-out for its sci-fi western The Adventures of Brisco County Jr., with the expectation that Brisco County Jr. would serve as the anchor of its Friday-night lineup. However, The X-Files proved to be significantly more successful, and would eventually run for nine seasons. By contrast, viewership for Brisco County Jr. declined throughout the season, and the show was cancelled. Fox attempted to use other sci-fi shows as a lead-in for The X-Files (such as Sliders and VR.5), but they were similarly unsuccessful.
A weak lead-in can have an impact on the viewership of programs that follow; NBC's 2009 attempt to strip the talk show The Jay Leno Show (a spiritual succes
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he talk show The Jay Leno Show (a spiritual successor to Leno's tenure of The Tonight Show after Conan O'Brien succeeded him) in a 10:00 p.m. ET/PT timeslot proved detrimental to the viewership of late local newscasts on its affiliates. NBC subsequently announced plans to shorten The Jay Leno Show to a half hour and move it to 11:35 p.m. ET/PT in late-February 2010, displacing The Tonight Show from its traditional timeslot. This proposal led to a public conflict between O'Brien and NBC, and ultimately resulted in his departure from the network, and the reinstatement of Jay Leno as host of The Tonight Show.
=== Blocks ===
Block programming is the practice of scheduling a group of complementary programs together. Blocks are typically built around specific genres (i.e. a block focusing specifically on sitcoms), target audiences, or other factors, with their programming often promoted collectively under blanket titles (such as ABC's "TGIF" lineup, All TV's "Jeepney TV sa All TV", and NB
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F" lineup, All TV's "Jeepney TV sa All TV", and NBC's "Must See TV").
=== Bridging ===
Bridging is the practice of discouraging the audience from changing channels during the "junctions" between specific programs. This can be done, primarily, by airing promos for the next program near the end of the preceding program, such as during its credits, or reducing the length of the junction between two programs as much as possible (hot switching). The host of the next program may similarly make a brief appearance near the end of the preceding program (sometimes interacting directly with the host) to provide a preview; in news broadcasting, this is typically referred to as a "throw" or "toss".
A bridge was used by ABC between Roseanne and the December 1992 series premiere of The Jackie Thomas Show, a new sitcom co-created by Roseanne and Tom Arnold of Roseanne fame. A scene of the Connor family watching its opening on TV seamlessly transitioned into the program itself, with no junction in be
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ed into the program itself, with no junction in between. ABC commissioned a minute-by-minute Nielsen ratings report, which showed that the majority of viewers from Roseanne had been retained during the premiere.
Owing to both programs' news comedy formats, the Comedy Central program The Daily Show used newscast-style toss segments to promote its new spin-off and lead-out, The Colbert Report, in which host Jon Stewart would engage in a comedic conversation with the latter's host, Stephen Colbert, via split-screen. On the December 18, 2014 episode of The Daily Show, this segment was used to seamlessly segue into the series finale of The Colbert Report. At its conclusion, the show transitioned back to Stewart (giving the impression that the entire Colbert Report episode was merely a segment of The Daily Show), who concluded his show with its traditional closing segment "Your Moment of Zen" (which featured an outtake from a previous toss segment) as normal.
In some cases, a channel may int
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gment) as normal.
In some cases, a channel may intentionally allow a program to overrun into the next half-hour timeslot rather than end exactly on the half-hour, in order to discourage viewers from "surfing" away at traditional junction periods (since they had missed the beginnings of programs on other channels already). This can, however, cause disruptions with recorders if they are not aware of the scheduling (typically, digital video recorders can be configured to automatically record for a set length of time before and after a schedule's given timeslot in program guide data to account for possible variances). For a period, TBS intentionally scheduled all of its programs at 5 and 35 minutes past the hour rather than exactly on the half hour (a practice it marketed as "Turner Time"), to attract viewers tuning away from other channels.
=== Crossovers ===
Crossovers can be organized between multiple programs, in which a single storyline is extended across episodes of two or more se
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line is extended across episodes of two or more separate programs. Typically, these involve programs that form a single franchise or shared universe, such as NBC's Chicago franchise and Law & Order: Special Victims Unit (all created by Dick Wolf), and the ABC dramas Grey's Anatomy and Station 19 (both created by Shonda Rhimes).
=== Counterprogramming ===
Counterprogramming is the practice of deliberately scheduling programming to attract viewers away from another, major program. Counterprogramming efforts often involve scheduling a contrasting program of a different genre or demographic, targeting viewers who may not be interested in the major program (such as a sporting event, which typically draws a predominantly-male audience, against an awards show that attracts a predominantly-female audience). Despite frequently being among the top U.S. television broadcasts of all time, the Super Bowl has had a prominent history of being counterprogrammed in this manner. One of the most promi
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erprogrammed in this manner. One of the most prominent examples of this practice was Fox's 1992 airing of a special live episode of In Living Color against the game's halftime show.
Programs can also be counterprogrammed by a direct competitor in the same time slot, often resulting in the two programs attempting to attract viewers away from each other through publicity stunts and other tactics; these tactics have most notably been seen in counterprogramming efforts surrounding professional wrestling, including the Monday and Wednesday Night Wars of the 1990s and 2020s respectively.
In some cases, broadcasters may attempt to adjust their schedules in order to avert attempts at counterprogramming, such as getting a slightly earlier time slot (in the hope that once viewers have become committed to a show they will not switch channels), scheduling the competing program on a different night, or moving it to a different portion of the television season to avoid competition altogether.
===
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ion season to avoid competition altogether.
=== Dayparting ===
Dayparting is the practice of dividing the day into several parts, during each of which a different type program is appropriate for that time is aired. Daytime television shows are most often geared toward a particular demographic, and what the target audience typically engages in at that time.
=== Stripping ===
Stripping is the practice of running a single series in a consistent, daily time slot throughout the week, usually on weekdays. Daytime programs such as talk shows, court shows, game shows, and soap operas, are typically aired in a strip format. Outside of serial drama formats such as telenovelas where popular, strips are rarely used for first-run entertainment programming outside of limited events.
Syndicated reruns of network programs that originally aired on a weekly basis are often aired as strips. Shows that are syndicated in this way generally have to have run for several seasons (the rule of thumb is us
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e run for several seasons (the rule of thumb is usually 100 episodes) in order to have enough episodes to run without significant repeats.
=== Marathons ===
A marathon is the scheduling of a continuous, long-term block of programming as an event, usually devoted to airings of a single program or film franchise. When conducted using television series, a marathon may either consist of episodes aired in sequential order, or focus on episodes sharing specific themes.
Marathons are often aired on holidays (such as Syfy's annual The Twilight Zone marathon on New Year's Day, and Game Show Network airing a Charles Nelson Reilly-hosted marathon of game show series finales on New Year's Eve in 1999), as counterprogramming for major events airing on other channels (such as the Super Bowl in the U.S.), to lead into new episodes of a series, or to commemorate milestones/events surrounding a specific series or franchise (such as an anniversary, or the network's acquisition of rights to broadcast
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the network's acquisition of rights to broadcast a certain series or franchise). Some marathons may focus on the roles of a specific entertainer; the death of Betty White resulted in several networks scheduling marathons of programming on or around January 17, 2022—which would have been White's 100th birthday—featuring her television appearances, such as Hallmark Channel airing a marathon of The Golden Girls, and both Buzzr and Game Show Network airing marathons of her game show appearances.
While longer marathons are typically reserved for major events, the popularization of binge-watching via streaming services in the 2010s led to many U.S. cable networks adopting marathon-like blocks of programs as their regular schedule. To compete with the release practices of streaming services, TBS premiered entire seasons of its police sitcom Angie Tribeca in a marathon format. Similarly, free ad-supported streaming television (FAST) services often feature linear channels that are narrowly-foc
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ften feature linear channels that are narrowly-focused towards specific programs or franchises.
=== Theming ===
A broadcaster may temporarily dedicate all or parts of its schedule over a period of time to a specific theme. A well-known instance of a themed lineup is Discovery Channel's annual "Shark Week". Themed schedules are a common practice around major holidays—such as Valentine's Day, Halloween, and Christmas—where channels may air episodes of programs, specials, and films that relate to the holiday. Channels may also air marathons of their signature programs and film rights to target viewers who are on vacation.
The U.S. basic cable networks Freeform (25 Days of Christmas, 31 Days of Halloween) and Hallmark Channel are known for broadcasting long-term holiday programming events. After experiencing success with its Countdown to Christmas event, Hallmark Channel adopted a practice of dividing its programming into similarly-branded "seasons" year-round, which are accompanied by t
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d "seasons" year-round, which are accompanied by thematically appropriate original series and television films. This strategy was part of an effort to position the channel as "a year-round destination for celebrations", and is synergistic with Hallmark Cards' core greeting card and collectibles businesses.
=== Time slot ===
A show's time slot or place in the schedule could be crucial to its success or failure; generally, earlier prime time slots have a stronger appeal towards family viewing and younger demographics, while later time slots generally appeal more towards older demographics. Some time slots, colloquially known as "graveyard slots" or "death slots", are prone to having smaller potential audiences (with one such example in the U.S. being Friday nights), or insurmountable competition from highly rated series.
== See also ==
Audience flow
Broadcast clock
Effects of time zones on North American broadcasting
Electronic media
Fall schedule
Interstitial program
Radio Computing
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Fall schedule
Interstitial program
Radio Computing Services – automated scheduling for radio stations
Timeshift channel
TV Guide
TV listings
== References ==
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A programming game is a video game that incorporates elements of computer programming, enabling the player to direct otherwise autonomous units within the game to follow commands in a domain-specific programming language, often represented as a visual language to simplify the programming metaphor. Programming games broadly fall into two areas: single-player games where the programming elements either make up part of or the whole of a puzzle game, and multiplayer games where the player's automated program is pitted against other players' programs.
== As puzzle games ==
Early games in the genre include System 15000 and Hacker, released in 1984 and 1985 respectively.
Programming games have been used as part of puzzle games, challenging the player to achieve a specific result once the program starts operating. An example of such a game is SpaceChem, where the player must use its visual language to manipulate two waldos as to disassemble and reassemble chemical molecules. In such games, p
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nd reassemble chemical molecules. In such games, players are able to test and debug their program as often as necessary until they find a solution that works. Many of these games encourage the player to find the most efficient program, measured by the number of timesteps needed or number of commands required. Other similar games include Human Resource Machine, Infinifactory, and TIS-100. Zachtronics is a video game development company known for its programming-centric puzzle games.
Other games incorporate the elements of programming as portions of puzzles in the larger game. For example, Hack 'n' Slash include a metaphor of being able to access the internal programs and variables of objects represented in the game world, pausing the rest of the game as the player engages this programming interface, and modify the object's program as to progress further; this might be changing the state of an object from being indestructible to destructible. Other similar games with this type of program
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ble. Other similar games with this type of programming approach include Transistor, else Heart.Break(), Glitchspace, and Pony Island.
Another approach used in some graphical games with programming elements is to present the player with a command line interface to issue orders via a domain-specific language to direct objects within the game, allowing the player to reissue commands as the situation changes rather than crafting a pre-made program. Games like Quadrilateral Cowboy and Duskers have the user command several small robotic creatures in tandem through the language of code to reach a certain goal. Hackmud presents the player with a simulated mainframe interface through which they issue commands to progress forward.
== As competitive games ==
Many programming games involve controlling entities such as robots, tanks or bacteria which seek to destroy each other. Such games can be considered environments of digital organisms, related to artificial life simulations. An early example
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d to artificial life simulations. An early example is Core War (1984), where programs written in a standardized assembly-like language battle for space in a finite memory (virtual magnetic cores). Players are given tools to develop and test out their programs within the game's domain-specific language before submitting the program to a central server. The server then executes the program against others and reports the results to the player, from which they can make changes or improvements to the program.
There are different tournaments and leagues for the programming games where the characters can compete with each other. Usually a script is optimized for a special strategy. Similar approaches are used for more traditional games; the World Computer Chess Championship consists of matches between programs written for the abstract strategy game of chess.
The competitive programming game has also found its way to various board games such as RoboRally or Robot Turtles, typically where a pro
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RoboRally or Robot Turtles, typically where a program becomes a premade deck of playing cards played one by one to execute that code.
Researchers presented RoboCode as a "problem-based learning" substrate for teaching programming.
== Related areas ==
Open world games that feature the ability for players to construct environments from an array of building blocks have often been used by more advanced players to construct logic circuits and more advanced programs from the fundamental blocks. Minecraft is one such example, as while the game provides a limited set of blocks that mimic switches and electric circuits, users have been able to create basic functional computers within the virtual world, and at least one modification is aimed to teach children how to program on the virtual computer in a simplistic language.
Several sites, such as Codecademy, help to teach real-world programming languages through gamification, where video game principles are used to motivate the user.
== See
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rinciples are used to motivate the user.
== See also ==
Programming games category
List of digital organism simulators
Visual programming language
Zachtronics
== References ==
== External links ==
The Programming Games Wiki
Many inactive programming games listed at AIforge
A History of Programming Games
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A computer program is a sequence or set of instructions in a programming language for a computer to execute. It is one component of software, which also includes documentation and other intangible components.
A computer program in its human-readable form is called source code. Source code needs another computer program to execute because computers can only execute their native machine instructions. Therefore, source code may be translated to machine instructions using a compiler written for the language. (Assembly language programs are translated using an assembler.) The resulting file is called an executable. Alternatively, source code may execute within an interpreter written for the language.
If the executable is requested for execution, then the operating system loads it into memory and starts a process. The central processing unit will soon switch to this process so it can fetch, decode, and then execute each machine instruction.
If the source code is requested for execution, then
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f the source code is requested for execution, then the operating system loads the corresponding interpreter into memory and starts a process. The interpreter then loads the source code into memory to translate and execute each statement. Running the source code is slower than running an executable. Moreover, the interpreter must be installed on the computer.
== Example computer program ==
The "Hello, World!" program is used to illustrate a language's basic syntax. The syntax of the language BASIC (1964) was intentionally limited to make the language easy to learn. For example, variables are not declared before being used. Also, variables are automatically initialized to zero. Here is an example computer program, in Basic, to average a list of numbers:
Once the mechanics of basic computer programming are learned, more sophisticated and powerful languages are available to build large computer systems.
== History ==
Improvements in software development are the result of improvements
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oftware development are the result of improvements in computer hardware. At each stage in hardware's history, the task of computer programming changed dramatically.
=== Analytical Engine ===
In 1837, Jacquard's loom inspired Charles Babbage to attempt to build the Analytical Engine.
The names of the components of the calculating device were borrowed from the textile industry. In the textile industry, yarn was brought from the store to be milled. The device had a store which consisted of memory to hold 1,000 numbers of 50 decimal digits each. Numbers from the store were transferred to the mill for processing. The engine was programmed using two sets of perforated cards. One set directed the operation and the other set inputted the variables. However, the thousands of cogged wheels and gears never fully worked together.
Ada Lovelace worked for Charles Babbage to create a description of the Analytical Engine (1843). The description contained Note G which completely detailed a method fo
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ained Note G which completely detailed a method for calculating Bernoulli numbers using the Analytical Engine. This note is recognized by some historians as the world's first computer program.
=== Universal Turing machine ===
In 1936, Alan Turing introduced the Universal Turing machine, a theoretical device that can model every computation.
It is a finite-state machine that has an infinitely long read/write tape. The machine can move the tape back and forth, changing its contents as it performs an algorithm. The machine starts in the initial state, goes through a sequence of steps, and halts when it encounters the halt state. All present-day computers are Turing complete.
=== ENIAC ===
The Electronic Numerical Integrator And Computer (ENIAC) was built between July 1943 and Fall 1945. It was a Turing complete, general-purpose computer that used 17,468 vacuum tubes to create the circuits. At its core, it was a series of Pascalines wired together. Its 40 units weighed 30 tons, occup
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ired together. Its 40 units weighed 30 tons, occupied 1,800 square feet (167 m2), and consumed $650 per hour (in 1940s currency) in electricity when idle. It had 20 base-10 accumulators. Programming the ENIAC took up to two months. Three function tables were on wheels and needed to be rolled to fixed function panels. Function tables were connected to function panels by plugging heavy black cables into plugboards. Each function table had 728 rotating knobs. Programming the ENIAC also involved setting some of the 3,000 switches. Debugging a program took a week. It ran from 1947 until 1955 at Aberdeen Proving Ground, calculating hydrogen bomb parameters, predicting weather patterns, and producing firing tables to aim artillery guns.
=== Stored-program computers ===
Instead of plugging in cords and turning switches, a stored-program computer loads its instructions into memory just like it loads its data into memory. As a result, the computer could be programmed quickly and perform calcul
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ter could be programmed quickly and perform calculations at very fast speeds. Presper Eckert and John Mauchly built the ENIAC. The two engineers introduced the stored-program concept in a three-page memo dated February 1944. Later, in September 1944, John von Neumann began working on the ENIAC project. On June 30, 1945, von Neumann published the First Draft of a Report on the EDVAC, which equated the structures of the computer with the structures of the human brain. The design became known as the von Neumann architecture. The architecture was simultaneously deployed in the constructions of the EDVAC and EDSAC computers in 1949.
The IBM System/360 (1964) was a family of computers, each having the same instruction set architecture. The Model 20 was the smallest and least expensive. Customers could upgrade and retain the same application software. The Model 195 was the most premium. Each System/360 model featured multiprogramming—having multiple processes in memory at once. When one proc
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ultiple processes in memory at once. When one process was waiting for input/output, another could compute.
IBM planned for each model to be programmed using PL/1. A committee was formed that included COBOL, Fortran and ALGOL programmers. The purpose was to develop a language that was comprehensive, easy to use, extendible, and would replace Cobol and Fortran. The result was a large and complex language that took a long time to compile.
Computers manufactured until the 1970s had front-panel switches for manual programming. The computer program was written on paper for reference. An instruction was represented by a configuration of on/off settings. After setting the configuration, an execute button was pressed. This process was then repeated. Computer programs also were automatically inputted via paper tape, punched cards or magnetic-tape. After the medium was loaded, the starting address was set via switches, and the execute button was pressed.
=== Very Large Scale Integration ===
A
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pressed.
=== Very Large Scale Integration ===
A major milestone in software development was the invention of the Very Large Scale Integration (VLSI) circuit (1964).
Robert Noyce, co-founder of Fairchild Semiconductor (1957) and Intel (1968), achieved a technological improvement to refine the production of field-effect transistors (1963). The goal is to alter the electrical resistivity and conductivity of a semiconductor junction. First, naturally occurring silicate minerals are converted into polysilicon rods using the Siemens process. The Czochralski process then converts the rods into a monocrystalline silicon, boule crystal. The crystal is then thinly sliced to form a wafer substrate. The planar process of photolithography then integrates unipolar transistors, capacitors, diodes, and resistors onto the wafer to build a matrix of metal–oxide–semiconductor (MOS) transistors. The MOS transistor is the primary component in integrated circuit chips.
Originally, integrated circuit chip
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circuit chips.
Originally, integrated circuit chips had their function set during manufacturing. During the 1960s, controlling the electrical flow migrated to programming a matrix of read-only memory (ROM). The matrix resembled a two-dimensional array of fuses. The process to embed instructions onto the matrix was to burn out the unneeded connections. There were so many connections, firmware programmers wrote a computer program on another chip to oversee the burning. The technology became known as Programmable ROM. In 1971, Intel installed the computer program onto the chip and named it the Intel 4004 microprocessor.
The terms microprocessor and central processing unit (CPU) are now used interchangeably. However, CPUs predate microprocessors. For example, the IBM System/360 (1964) had a CPU made from circuit boards containing discrete components on ceramic substrates.
=== x86 series ===
In 1978, the modern software development environment began when Intel upgraded the Intel 8080 to
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onment began when Intel upgraded the Intel 8080 to the Intel 8086. Intel simplified the Intel 8086 to manufacture the cheaper Intel 8088. IBM embraced the Intel 8088 when they entered the personal computer market (1981). As consumer demand for personal computers increased, so did Intel's microprocessor development. The succession of development is known as the x86 series. The x86 assembly language is a family of backward-compatible machine instructions. Machine instructions created in earlier microprocessors were retained throughout microprocessor upgrades. This enabled consumers to purchase new computers without having to purchase new application software. The major categories of instructions are:
Memory instructions to set and access numbers and strings in random-access memory.
Integer arithmetic logic unit (ALU) instructions to perform the primary arithmetic operations on integers.
Floating point ALU instructions to perform the primary arithmetic operations on real numbers.
Call s
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mary arithmetic operations on real numbers.
Call stack instructions to push and pop words needed to allocate memory and interface with functions.
Single instruction, multiple data (SIMD) instructions to increase speed when multiple processors are available to perform the same algorithm on an array of data.
=== Changing programming environment ===
VLSI circuits enabled the programming environment to advance from a computer terminal (until the 1990s) to a graphical user interface (GUI) computer. Computer terminals limited programmers to a single shell running in a command-line environment. During the 1970s, full-screen source code editing became possible through a text-based user interface. Regardless of the technology available, the goal is to program in a programming language.
== Programming paradigms and languages ==
Programming language features exist to provide building blocks to be combined to express programming ideals. Ideally, a programming language should:
express ideas d
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y, a programming language should:
express ideas directly in the code.
express independent ideas independently.
express relationships among ideas directly in the code.
combine ideas freely.
combine ideas only where combinations make sense.
express simple ideas simply.
The programming style of a programming language to provide these building blocks may be categorized into programming paradigms. For example, different paradigms may differentiate:
procedural languages, functional languages, and logical languages.
different levels of data abstraction.
different levels of class hierarchy.
different levels of input datatypes, as in container types and generic programming.
Each of these programming styles has contributed to the synthesis of different programming languages.
A programming language is a set of keywords, symbols, identifiers, and rules by which programmers can communicate instructions to the computer. They follow a set of rules called a syntax.
Keywords are reserved words to fo
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alled a syntax.
Keywords are reserved words to form declarations and statements.
Symbols are characters to form operations, assignments, control flow, and delimiters.
Identifiers are words created by programmers to form constants, variable names, structure names, and function names.
Syntax Rules are defined in the Backus–Naur form.
Programming languages get their basis from formal languages. The purpose of defining a solution in terms of its formal language is to generate an algorithm to solve the underlining problem. An algorithm is a sequence of simple instructions that solve a problem.
=== Generations of programming language ===
The evolution of programming languages began when the EDSAC (1949) used the first stored computer program in its von Neumann architecture. Programming the EDSAC was in the first generation of programming language.
The first generation of programming language is machine language. Machine language requires the programmer to enter instructions using instru
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the programmer to enter instructions using instruction numbers called machine code. For example, the ADD operation on the PDP-11 has instruction number 24576.
The second generation of programming language is assembly language. Assembly language allows the programmer to use mnemonic instructions instead of remembering instruction numbers. An assembler translates each assembly language mnemonic into its machine language number. For example, on the PDP-11, the operation 24576 can be referenced as ADD in the source code. The four basic arithmetic operations have assembly instructions like ADD, SUB, MUL, and DIV. Computers also have instructions like DW (Define Word) to reserve memory cells. Then the MOV instruction can copy integers between registers and memory.
The basic structure of an assembly language statement is a label, operation, operand, and comment.
Labels allow the programmer to work with variable names. The assembler will later translate labels into physical memory addresses.
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translate labels into physical memory addresses.
Operations allow the programmer to work with mnemonics. The assembler will later translate mnemonics into instruction numbers.
Operands tell the assembler which data the operation will process.
Comments allow the programmer to articulate a narrative because the instructions alone are vague.
The key characteristic of an assembly language program is it forms a one-to-one mapping to its corresponding machine language target.
The third generation of programming language uses compilers and interpreters to execute computer programs. The distinguishing feature of a third generation language is its independence from particular hardware. Early languages include Fortran (1958), COBOL (1959), ALGOL (1960), and BASIC (1964). In 1973, the C programming language emerged as a high-level language that produced efficient machine language instructions. Whereas third-generation languages historically generated many machine instructions for each statement,
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ated many machine instructions for each statement, C has statements that may generate a single machine instruction. Moreover, an optimizing compiler might overrule the programmer and produce fewer machine instructions than statements. Today, an entire paradigm of languages fill the imperative, third generation spectrum.
The fourth generation of programming language emphasizes what output results are desired, rather than how programming statements should be constructed. Declarative languages attempt to limit side effects and allow programmers to write code with relatively few errors. One popular fourth generation language is called Structured Query Language (SQL). Database developers no longer need to process each database record one at a time. Also, a simple select statement can generate output records without having to understand how they are retrieved.
=== Imperative languages ===
Imperative languages specify a sequential algorithm using declarations, expressions, and statements:
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using declarations, expressions, and statements:
A declaration introduces a variable name to the computer program and assigns it to a datatype – for example: var x: integer;
An expression yields a value – for example: 2 + 2 yields 4
A statement might assign an expression to a variable or use the value of a variable to alter the program's control flow – for example: x := 2 + 2; if x = 4 then do_something();
==== Fortran ====
FORTRAN (1958) was unveiled as "The IBM Mathematical FORmula TRANslating system". It was designed for scientific calculations, without string handling facilities. Along with declarations, expressions, and statements, it supported:
arrays.
subroutines.
"do" loops.
It succeeded because:
programming and debugging costs were below computer running costs.
it was supported by IBM.
applications at the time were scientific.
However, non-IBM vendors also wrote Fortran compilers, but with a syntax that would likely fail IBM's compiler. The American National Standards In
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IBM's compiler. The American National Standards Institute (ANSI) developed the first Fortran standard in 1966. In 1978, Fortran 77 became the standard until 1991. Fortran 90 supports:
records.
pointers to arrays.
==== COBOL ====
COBOL (1959) stands for "COmmon Business Oriented Language". Fortran manipulated symbols. It was soon realized that symbols did not need to be numbers, so strings were introduced. The US Department of Defense influenced COBOL's development, with Grace Hopper being a major contributor. The statements were English-like and verbose. The goal was to design a language so managers could read the programs. However, the lack of structured statements hindered this goal.
COBOL's development was tightly controlled, so dialects did not emerge to require ANSI standards. As a consequence, it was not changed for 15 years until 1974. The 1990s version did make consequential changes, like object-oriented programming.
==== Algol ====
ALGOL (1960) stands for "ALGOrithmic Lan
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lgol ====
ALGOL (1960) stands for "ALGOrithmic Language". It had a profound influence on programming language design. Emerging from a committee of European and American programming language experts, it used standard mathematical notation and had a readable, structured design. Algol was first to define its syntax using the Backus–Naur form. This led to syntax-directed compilers. It added features like:
block structure, where variables were local to their block.
arrays with variable bounds.
"for" loops.
functions.
recursion.
Algol's direct descendants include Pascal, Modula-2, Ada, Delphi and Oberon on one branch. On another branch the descendants include C, C++ and Java.
==== Basic ====
BASIC (1964) stands for "Beginner's All-Purpose Symbolic Instruction Code". It was developed at Dartmouth College for all of their students to learn. If a student did not go on to a more powerful language, the student would still remember Basic. A Basic interpreter was installed in the microcomputers
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c interpreter was installed in the microcomputers manufactured in the late 1970s. As the microcomputer industry grew, so did the language.
Basic pioneered the interactive session. It offered operating system commands within its environment:
The 'new' command created an empty slate.
Statements evaluated immediately.
Statements could be programmed by preceding them with line numbers.
The 'list' command displayed the program.
The 'run' command executed the program.
However, the Basic syntax was too simple for large programs. Recent dialects added structure and object-oriented extensions. Microsoft's Visual Basic is still widely used and produces a graphical user interface.
==== C ====
C programming language (1973) got its name because the language BCPL was replaced with B, and AT&T Bell Labs called the next version "C". Its purpose was to write the UNIX operating system. C is a relatively small language, making it easy to write compilers. Its growth mirrored the hardware growth in the
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s. Its growth mirrored the hardware growth in the 1980s. Its growth also was because it has the facilities of assembly language, but uses a high-level syntax. It added advanced features like:
inline assembler.
arithmetic on pointers.
pointers to functions.
bit operations.
freely combining complex operators.
C allows the programmer to control which region of memory data is to be stored. Global variables and static variables require the fewest clock cycles to store. The stack is automatically used for the standard variable declarations. Heap memory is returned to a pointer variable from the malloc() function.
The global and static data region is located just above the program region. (The program region is technically called the text region. It is where machine instructions are stored.)
The global and static data region is technically two regions. One region is called the initialized data segment, where variables declared with default values are stored. The other region is called the
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values are stored. The other region is called the block started by segment, where variables declared without default values are stored.
Variables stored in the global and static data region have their addresses set at compile time. They retain their values throughout the life of the process.
The global and static region stores the global variables that are declared on top of (outside) the main() function. Global variables are visible to main() and every other function in the source code.
On the other hand, variable declarations inside of main(), other functions, or within { } block delimiters are local variables. Local variables also include formal parameter variables. Parameter variables are enclosed within the parenthesis of a function definition. Parameters provide an interface to the function.
Local variables declared using the static prefix are also stored in the global and static data region. Unlike global variables, static variables are only visible within the function or block.
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les are only visible within the function or block. Static variables always retain their value. An example usage would be the function int increment_counter(){static int counter = 0; counter++; return counter;}
The stack region is a contiguous block of memory located near the top memory address. Variables placed in the stack are populated from top to bottom. A stack pointer is a special-purpose register that keeps track of the last memory address populated. Variables are placed into the stack via the assembly language PUSH instruction. Therefore, the addresses of these variables are set during runtime. The method for stack variables to lose their scope is via the POP instruction.
Local variables declared without the static prefix, including formal parameter variables, are called automatic variables and are stored in the stack. They are visible inside the function or block and lose their scope upon exiting the function or block.
The heap region is located below the stack. It is populated
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region is located below the stack. It is populated from the bottom to the top. The operating system manages the heap using a heap pointer and a list of allocated memory blocks. Like the stack, the addresses of heap variables are set during runtime. An out of memory error occurs when the heap pointer and the stack pointer meet.
C provides the malloc() library function to allocate heap memory. Populating the heap with data is an additional copy function. Variables stored in the heap are economically passed to functions using pointers. Without pointers, the entire block of data would have to be passed to the function via the stack.
==== C++ ====
In the 1970s, software engineers needed language support to break large projects down into modules. One obvious feature was to decompose large projects physically into separate files. A less obvious feature was to decompose large projects logically into abstract data types. At the time, languages supported concrete (scalar) datatypes like intege
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supported concrete (scalar) datatypes like integer numbers, floating-point numbers, and strings of characters. Abstract datatypes are structures of concrete datatypes, with a new name assigned. For example, a list of integers could be called integer_list.
In object-oriented jargon, abstract datatypes are called classes. However, a class is only a definition; no memory is allocated. When memory is allocated to a class and bound to an identifier, it is called an object.
Object-oriented imperative languages developed by combining the need for classes and the need for safe functional programming. A function, in an object-oriented language, is assigned to a class. An assigned function is then referred to as a method, member function, or operation. Object-oriented programming is executing operations on objects.
Object-oriented languages support a syntax to model subset/superset relationships. In set theory, an element of a subset inherits all the attributes contained in the superset. For ex
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l the attributes contained in the superset. For example, a student is a person. Therefore, the set of students is a subset of the set of persons. As a result, students inherit all the attributes common to all persons. Additionally, students have unique attributes that other people do not have. Object-oriented languages model subset/superset relationships using inheritance. Object-oriented programming became the dominant language paradigm by the late 1990s.
C++ (1985) was originally called "C with Classes". It was designed to expand C's capabilities by adding the object-oriented facilities of the language Simula.
An object-oriented module is composed of two files. The definitions file is called the header file. Here is a C++ header file for the GRADE class in a simple school application:
A constructor operation is a function with the same name as the class name. It is executed when the calling operation executes the new statement.
A module's other file is the source file. Here is a C++
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ule's other file is the source file. Here is a C++ source file for the GRADE class in a simple school application:
Here is a C++ header file for the PERSON class in a simple school application:
Here is a C++ source file for the PERSON class in a simple school application:
Here is a C++ header file for the STUDENT class in a simple school application:
Here is a C++ source file for the STUDENT class in a simple school application:
Here is a driver program for demonstration:
Here is a makefile to compile everything:
=== Declarative languages ===
Imperative languages have one major criticism: assigning an expression to a non-local variable may produce an unintended side effect. Declarative languages generally omit the assignment statement and the control flow. They describe what computation should be performed and not how to compute it. Two broad categories of declarative languages are functional languages and logical languages.
The principle behind a functional language is to use
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e principle behind a functional language is to use lambda calculus as a guide for a well defined semantic. In mathematics, a function is a rule that maps elements from an expression to a range of values. Consider the function:
times_10(x) = 10 * x
The expression 10 * x is mapped by the function times_10() to a range of values. One value happens to be 20. This occurs when x is 2. So, the application of the function is mathematically written as:
times_10(2) = 20
A functional language compiler will not store this value in a variable. Instead, it will push the value onto the computer's stack before setting the program counter back to the calling function. The calling function will then pop the value from the stack.
Imperative languages do support functions. Therefore, functional programming can be achieved in an imperative language, if the programmer uses discipline. However, a functional language will force this discipline onto the programmer through its syntax. Functional languages have
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mer through its syntax. Functional languages have a syntax tailored to emphasize the what.
A functional program is developed with a set of primitive functions followed by a single driver function. Consider the snippet:
function max( a, b ){/* code omitted */}
function min( a, b ){/* code omitted */}
function range( a, b, c ) {
return max( a, max( b, c ) ) - min( a, min( b, c ) );
}
The primitives are max() and min(). The driver function is range(). Executing:
put( range( 10, 4, 7) ); will output 6.
Functional languages are used in computer science research to explore new language features. Moreover, their lack of side-effects have made them popular in parallel programming and concurrent programming. However, application developers prefer the object-oriented features of imperative languages.
==== Lisp ====
Lisp (1958) stands for "LISt Processor". It is tailored to process lists. A full structure of the data is formed by building lists of lists. In memory, a tree data structure is bui
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of lists. In memory, a tree data structure is built. Internally, the tree structure lends nicely for recursive functions. The syntax to build a tree is to enclose the space-separated elements within parenthesis. The following is a list of three elements. The first two elements are themselves lists of two elements:
((A B) (HELLO WORLD) 94)
Lisp has functions to extract and reconstruct elements. The function head() returns a list containing the first element in the list. The function tail() returns a list containing everything but the first element. The function cons() returns a list that is the concatenation of other lists. Therefore, the following expression will return the list x:
cons(head(x), tail(x))
One drawback of Lisp is when many functions are nested, the parentheses may look confusing. Modern Lisp environments help ensure parenthesis match. As an aside, Lisp does support the imperative language operations of the assignment statement and goto loops. Also, Lisp is not concerned
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tement and goto loops. Also, Lisp is not concerned with the datatype of the elements at compile time. Instead, it assigns (and may reassign) the datatypes at runtime. Assigning the datatype at runtime is called dynamic binding. Whereas dynamic binding increases the language's flexibility, programming errors may linger until late in the software development process.
Writing large, reliable, and readable Lisp programs requires forethought. If properly planned, the program may be much shorter than an equivalent imperative language program. Lisp is widely used in artificial intelligence. However, its usage has been accepted only because it has imperative language operations, making unintended side-effects possible.
==== ML ====
ML (1973) stands for "Meta Language". ML checks to make sure only data of the same type are compared with one another. For example, this function has one input parameter (an integer) and returns an integer:
ML is not parenthesis-eccentric like Lisp. The following
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not parenthesis-eccentric like Lisp. The following is an application of times_10():
times_10 2
It returns "20 : int". (Both the results and the datatype are returned.)
Like Lisp, ML is tailored to process lists. Unlike Lisp, each element is the same datatype. Moreover, ML assigns the datatype of an element at compile time. Assigning the datatype at compile time is called static binding. Static binding increases reliability because the compiler checks the context of variables before they are used.
==== Prolog ====
Prolog (1972) stands for "PROgramming in LOGic". It is a logic programming language, based on formal logic. The language was developed by Alain Colmerauer and Philippe Roussel in Marseille, France. It is an implementation of Selective Linear Definite clause resolution, pioneered by Robert Kowalski and others at the University of Edinburgh.
The building blocks of a Prolog program are facts and rules. Here is a simple example:
After all the facts and rules are entered, then
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:
After all the facts and rules are entered, then a question can be asked:
Will Tom eat Jerry?
The following example shows how Prolog will convert a letter grade to its numeric value:
Here is a comprehensive example:
1) All dragons billow fire, or equivalently, a thing billows fire if the thing is a dragon:
2) A creature billows fire if one of its parents billows fire:
3) A thing X is a parent of a thing Y if X is the mother of Y or X is the father of Y:
4) A thing is a creature if the thing is a dragon:
5) Norberta is a dragon, and Puff is a creature. Norberta is the mother of Puff.
Rule (2) is a recursive (inductive) definition. It can be understood declaratively, without the need to understand how it is executed.
Rule (3) shows how functions are represented by using relations. Here, the mother and father functions ensure that every individual has only one mother and only one father.
Prolog is an untyped language. Nonetheless, inheritance can be represented by using predicat
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, inheritance can be represented by using predicates. Rule (4) asserts that a creature is a superclass of a dragon.
Questions are answered using backward reasoning. Given the question:
Prolog generates two answers :
Practical applications for Prolog are knowledge representation and problem solving in artificial intelligence.
=== Object-oriented programming ===
Object-oriented programming is a programming method to execute operations (functions) on objects. The basic idea is to group the characteristics of a phenomenon into an object container and give the container a name. The operations on the phenomenon are also grouped into the container. Object-oriented programming developed by combining the need for containers and the need for safe functional programming. This programming method need not be confined to an object-oriented language. In an object-oriented language, an object container is called a class. In a non-object-oriented language, a data structure (which is also known as a
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nguage, a data structure (which is also known as a record) may become an object container. To turn a data structure into an object container, operations need to be written specifically for the structure. The resulting structure is called an abstract datatype. However, inheritance will be missing. Nonetheless, this shortcoming can be overcome.
Here is a C programming language header file for the GRADE abstract datatype in a simple school application:
The grade_new() function performs the same algorithm as the C++ constructor operation.
Here is a C programming language source file for the GRADE abstract datatype in a simple school application:
In the constructor, the function calloc() is used instead of malloc() because each memory cell will be set to zero.
Here is a C programming language header file for the PERSON abstract datatype in a simple school application:
Here is a C programming language source file for the PERSON abstract datatype in a simple school application:
Here is a
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tatype in a simple school application:
Here is a C programming language header file for the STUDENT abstract datatype in a simple school application:
Here is a C programming language source file for the STUDENT abstract datatype in a simple school application:
Here is a driver program for demonstration:
Here is a makefile to compile everything:
The formal strategy to build object-oriented objects is to:
Identify the objects. Most likely these will be nouns.
Identify each object's attributes. What helps to describe the object?
Identify each object's actions. Most likely these will be verbs.
Identify the relationships from object to object. Most likely these will be verbs.
For example:
A person is a human identified by a name.
A grade is an achievement identified by a letter.
A student is a person who earns a grade.
=== Syntax and semantics ===
The syntax of a computer program is a list of production rules which form its grammar. A programming language's grammar correctly place
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. A programming language's grammar correctly places its declarations, expressions, and statements. Complementing the syntax of a language are its semantics. The semantics describe the meanings attached to various syntactic constructs. A syntactic construct may need a semantic description because a production rule may have an invalid interpretation. Also, different languages might have the same syntax; however, their behaviors may be different.
The syntax of a language is formally described by listing the production rules. Whereas the syntax of a natural language is extremely complicated, a subset of the English language can have this production rule listing:
a sentence is made up of a noun-phrase followed by a verb-phrase;
a noun-phrase is made up of an article followed by an adjective followed by a noun;
a verb-phrase is made up of a verb followed by a noun-phrase;
an article is 'the';
an adjective is 'big' or
an adjective is 'small';
a noun is 'cat' or
a noun is 'mouse';
a verb is '
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a noun is 'cat' or
a noun is 'mouse';
a verb is 'eats';
The words in bold-face are known as non-terminals. The words in 'single quotes' are known as terminals.
From this production rule listing, complete sentences may be formed using a series of replacements. The process is to replace non-terminals with either a valid non-terminal or a valid terminal. The replacement process repeats until only terminals remain. One valid sentence is:
sentence
noun-phrase verb-phrase
article adjective noun verb-phrase
the adjective noun verb-phrase
the big noun verb-phrase
the big cat verb-phrase
the big cat verb noun-phrase
the big cat eats noun-phrase
the big cat eats article adjective noun
the big cat eats the adjective noun
the big cat eats the small noun
the big cat eats the small mouse
However, another combination results in an invalid sentence:
the small mouse eats the big cat
Therefore, a semantic is necessary to correctly describe the meaning of an eat activity.
One production rule listing m
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of an eat activity.
One production rule listing method is called the Backus–Naur form (BNF). BNF describes the syntax of a language and itself has a syntax. This recursive definition is an example of a metalanguage. The syntax of BNF includes:
::= which translates to is made up of a[n] when a non-terminal is to its right. It translates to is when a terminal is to its right.
| which translates to or.
< and > which surround non-terminals.
Using BNF, a subset of the English language can have this production rule listing:
Using BNF, a signed-integer has the production rule listing:
Notice the recursive production rule:
This allows for an infinite number of possibilities. Therefore, a semantic is necessary to describe a limitation of the number of digits.
Notice the leading zero possibility in the production rules:
Therefore, a semantic is necessary to describe that leading zeros need to be ignored.
Two formal methods are available to describe semantics. They are denotational semantic
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describe semantics. They are denotational semantics and axiomatic semantics.
== Software engineering and computer programming ==
Software engineering is a variety of techniques to produce quality computer programs. Computer programming is the process of writing or editing source code. In a formal environment, a systems analyst will gather information from managers about all the organization's processes to automate. This professional then prepares a detailed plan for the new or modified system. The plan is analogous to an architect's blueprint.
=== Performance objectives ===
The systems analyst has the objective to deliver the right information to the right person at the right time. The critical factors to achieve this objective are:
The quality of the output. Is the output useful for decision-making?
The accuracy of the output. Does it reflect the true situation?
The format of the output. Is the output easily understood?
The speed of the output. Time-sensitive information is impo
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of the output. Time-sensitive information is important when communicating with the customer in real time.
=== Cost objectives ===
Achieving performance objectives should be balanced with all of the costs, including:
Development costs.
Uniqueness costs. A reusable system may be expensive. However, it might be preferred over a limited-use system.
Hardware costs.
Operating costs.
Applying a systems development process will mitigate the axiom: the later in the process an error is detected, the more expensive it is to correct.
=== Waterfall model ===
The waterfall model is an implementation of a systems development process. As the waterfall label implies, the basic phases overlap each other:
The investigation phase is to understand the underlying problem.
The analysis phase is to understand the possible solutions.
The design phase is to plan the best solution.
The implementation phase is to program the best solution.
The maintenance phase lasts throughout the life of the system. Chan
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hase lasts throughout the life of the system. Changes to the system after it is deployed may be necessary. Faults may exist, including specification faults, design faults, or coding faults. Improvements may be necessary. Adaption may be necessary to react to a changing environment.
=== Computer programmer ===
A computer programmer is a specialist responsible for writing or modifying the source code to implement the detailed plan. A programming team is likely to be needed because most systems are too large to be completed by a single programmer. However, adding programmers to a project may not shorten the completion time. Instead, it may lower the quality of the system. To be effective, program modules need to be defined and distributed to team members. Also, team members must interact with one another in a meaningful and effective way.
Computer programmers may be programming in the small: programming within a single module. Chances are a module will execute modules located in other s
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e a module will execute modules located in other source code files. Therefore, computer programmers may be programming in the large: programming modules so they will effectively couple with each other. Programming-in-the-large includes contributing to the application programming interface (API).
=== Program modules ===
Modular programming is a technique to refine imperative language programs. Refined programs may reduce the software size, separate responsibilities, and thereby mitigate software aging. A program module is a sequence of statements that are bounded within a block and together identified by a name. Modules have a function, context, and logic:
The function of a module is what it does.
The context of a module are the elements being performed upon.
The logic of a module is how it performs the function.
The module's name should be derived first by its function, then by its context. Its logic should not be part of the name. For example, function compute_square_root( x ) or f
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or example, function compute_square_root( x ) or function compute_square_root_integer( i : integer ) are appropriate module names. However, function compute_square_root_by_division( x ) is not.
The degree of interaction within a module is its level of cohesion. Cohesion is a judgment of the relationship between a module's name and its function. The degree of interaction between modules is the level of coupling. Coupling is a judgement of the relationship between a module's context and the elements being performed upon.
=== Cohesion ===
The levels of cohesion from worst to best are:
Coincidental Cohesion: A module has coincidental cohesion if it performs multiple functions, and the functions are completely unrelated. For example, function read_sales_record_print_next_line_convert_to_float(). Coincidental cohesion occurs in practice if management enforces silly rules. For example, "Every module will have between 35 and 50 executable statements."
Logical Cohesion: A module has logical
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atements."
Logical Cohesion: A module has logical cohesion if it has available a series of functions, but only one of them is executed. For example, function perform_arithmetic( perform_addition, a, b ).
Temporal Cohesion: A module has temporal cohesion if it performs functions related to time. One example, function initialize_variables_and_open_files(). Another example, stage_one(), stage_two(), ...
Procedural Cohesion: A module has procedural cohesion if it performs multiple loosely related functions. For example, function read_part_number_update_employee_record().
Communicational Cohesion: A module has communicational cohesion if it performs multiple closely related functions. For example, function read_part_number_update_sales_record().
Informational Cohesion: A module has informational cohesion if it performs multiple functions, but each function has its own entry and exit points. Moreover, the functions share the same data structure. Object-oriented classes work at this level.
Fu
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re. Object-oriented classes work at this level.
Functional Cohesion: a module has functional cohesion if it achieves a single goal working only on local variables. Moreover, it may be reusable in other contexts.
=== Coupling ===
The levels of coupling from worst to best are:
Content Coupling: A module has content coupling if it modifies a local variable of another function. COBOL used to do this with the alter verb.
Common Coupling: A module has common coupling if it modifies a global variable.
Control Coupling: A module has control coupling if another module can modify its control flow. For example, perform_arithmetic( perform_addition, a, b ). Instead, control should be on the makeup of the returned object.
Stamp Coupling: A module has stamp coupling if an element of a data structure passed as a parameter is modified. Object-oriented classes work at this level.
Data Coupling: A module has data coupling if all of its input parameters are needed and none of them are modified. Moreo
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rs are needed and none of them are modified. Moreover, the result of the function is returned as a single object.
=== Data flow analysis ===
Data flow analysis is a design method used to achieve modules of functional cohesion and data coupling. The input to the method is a data-flow diagram. A data-flow diagram is a set of ovals representing modules. Each module's name is displayed inside its oval. Modules may be at the executable level or the function level.
The diagram also has arrows connecting modules to each other. Arrows pointing into modules represent a set of inputs. Each module should have only one arrow pointing out from it to represent its single output object. (Optionally, an additional exception arrow points out.) A daisy chain of ovals will convey an entire algorithm. The input modules should start the diagram. The input modules should connect to the transform modules. The transform modules should connect to the output modules.
== Functional categories ==
Computer p
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modules.
== Functional categories ==
Computer programs may be categorized along functional lines. The main functional categories are application software and system software. System software includes the operating system, which couples computer hardware with application software. The purpose of the operating system is to provide an environment where application software executes in a convenient and efficient manner. Both application software and system software execute utility programs. At the hardware level, a microcode program controls the circuits throughout the central processing unit.
=== Application software ===
Application software is the key to unlocking the potential of the computer system. Enterprise application software bundles accounting, personnel, customer, and vendor applications. Examples include enterprise resource planning, customer relationship management, and supply chain management software.
Enterprise applications may be developed in-house as a one-of-a-kind
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tions may be developed in-house as a one-of-a-kind proprietary software. Alternatively, they may be purchased as off-the-shelf software. Purchased software may be modified to provide custom software. If the application is customized, then either the company's resources are used or the resources are outsourced. Outsourced software development may be from the original software vendor or a third-party developer.
The potential advantages of in-house software are features and reports may be developed exactly to specification. Management may also be involved in the development process and offer a level of control. Management may decide to counteract a competitor's new initiative or implement a customer or vendor requirement. A merger or acquisition may necessitate enterprise software changes. The potential disadvantages of in-house software are time and resource costs may be extensive. Furthermore, risks concerning features and performance may be looming.
The potential advantages of off-the
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ay be looming.
The potential advantages of off-the-shelf software are upfront costs are identifiable, the basic needs should be fulfilled, and its performance and reliability have a track record. The potential disadvantages of off-the-shelf software are it may have unnecessary features that confuse end users, it may lack features the enterprise needs, and the data flow may not match the enterprise's work processes.
==== Application service provider ====
One approach to economically obtaining a customized enterprise application is through an application service provider. Specialty companies provide hardware, custom software, and end-user support. They may speed the development of new applications because they possess skilled information system staff. The biggest advantage is it frees in-house resources from staffing and managing complex computer projects. Many application service providers target small, fast-growing companies with limited information system resources. On the other han
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ted information system resources. On the other hand, larger companies with major systems will likely have their technical infrastructure in place. One risk is having to trust an external organization with sensitive information. Another risk is having to trust the provider's infrastructure reliability.
=== Operating system ===
An operating system is the low-level software that supports a computer's basic functions, such as scheduling processes and controlling peripherals.
In the 1950s, the programmer, who was also the operator, would write a program and run it. After the program finished executing, the output may have been printed, or it may have been punched onto paper tape or cards for later processing. More often than not the program did not work. The programmer then looked at the console lights and fiddled with the console switches. If less fortunate, a memory printout was made for further study. In the 1960s, programmers reduced the amount of wasted time by automating the operat
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the amount of wasted time by automating the operator's job. A program called an operating system was kept in the computer at all times.
The term operating system may refer to two levels of software. The operating system may refer to the kernel program that manages the processes, memory, and devices. More broadly, the operating system may refer to the entire package of the central software. The package includes a kernel program, command-line interpreter, graphical user interface, utility programs, and editor.
==== Kernel Program ====
The kernel's main purpose is to manage the limited resources of a computer:
The kernel program should perform process scheduling, which is also known as a context switch. The kernel creates a process control block when a computer program is selected for execution. However, an executing program gets exclusive access to the central processing unit only for a time slice. To provide each user with the appearance of continuous access, the kernel quickly pree
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ance of continuous access, the kernel quickly preempts each process control block to execute another one. The goal for system developers is to minimize dispatch latency.
The kernel program should perform memory management.
When the kernel initially loads an executable into memory, it divides the address space logically into regions. The kernel maintains a master-region table and many per-process-region (pregion) tables—one for each running process. These tables constitute the virtual address space. The master-region table is used to determine where its contents are located in physical memory. The pregion tables allow each process to have its own program (text) pregion, data pregion, and stack pregion.
The program pregion stores machine instructions. Since machine instructions do not change, the program pregion may be shared by many processes of the same executable.
To save time and memory, the kernel may load only blocks of execution instructions from the disk drive, not the entire ex
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nstructions from the disk drive, not the entire execution file completely.
The kernel is responsible for translating virtual addresses into physical addresses. The kernel may request data from the memory controller and, instead, receive a page fault. If so, the kernel accesses the memory management unit to populate the physical data region and translate the address.
The kernel allocates memory from the heap upon request by a process. When the process is finished with the memory, the process may request for it to be freed. If the process exits without requesting all allocated memory to be freed, then the kernel performs garbage collection to free the memory.
The kernel also ensures that a process only accesses its own memory, and not that of the kernel or other processes.
The kernel program should perform file system management. The kernel has instructions to create, retrieve, update, and delete files.
The kernel program should perform device management. The kernel provides programs to
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evice management. The kernel provides programs to standardize and simplify the interface to the mouse, keyboard, disk drives, printers, and other devices. Moreover, the kernel should arbitrate access to a device if two processes request it at the same time.
The kernel program should perform network management. The kernel transmits and receives packets on behalf of processes. One key service is to find an efficient route to the target system.
The kernel program should provide system level functions for programmers to use.
Programmers access files through a relatively simple interface that in turn executes a relatively complicated low-level I/O interface. The low-level interface includes file creation, file descriptors, file seeking, physical reading, and physical writing.
Programmers create processes through a relatively simple interface that in turn executes a relatively complicated low-level interface.
Programmers perform date/time arithmetic through a relatively simple interface that
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thmetic through a relatively simple interface that in turn executes a relatively complicated low-level time interface.
The kernel program should provide a communication channel between executing processes. For a large software system, it may be desirable to engineer the system into smaller processes. Processes may communicate with one another by sending and receiving signals.
Originally, operating systems were programmed in assembly; however, modern operating systems are typically written in higher-level languages like C, Objective-C, and Swift.
=== Utility program ===
A utility program is designed to aid system administration and software execution. Operating systems execute hardware utility programs to check the status of disk drives, memory, speakers, and printers. A utility program may optimize the placement of a file on a crowded disk. System utility programs monitor hardware and network performance. When a metric is outside an acceptable range, a trigger alert is generated.
Uti
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cceptable range, a trigger alert is generated.
Utility programs include compression programs so data files are stored on less disk space. Compressed programs also save time when data files are transmitted over the network. Utility programs can sort and merge data sets. Utility programs detect computer viruses.
=== Microcode program ===
A microcode program is the bottom-level interpreter that controls the data path of software-driven computers.
(Advances in hardware have migrated these operations to hardware execution circuits.) Microcode instructions allow the programmer to more easily implement the digital logic level—the computer's real hardware. The digital logic level is the boundary between computer science and computer engineering.
A logic gate is a tiny transistor that can return one of two signals: on or off.
Having one transistor forms the NOT gate.
Connecting two transistors in series forms the NAND gate.
Connecting two transistors in parallel forms the NOR gate.
Connecti
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ansistors in parallel forms the NOR gate.
Connecting a NOT gate to a NAND gate forms the AND gate.
Connecting a NOT gate to a NOR gate forms the OR gate.
These five gates form the building blocks of binary algebra—the digital logic functions of the computer.
Microcode instructions are mnemonics programmers may use to execute digital logic functions instead of forming them in binary algebra. They are stored in a central processing unit's (CPU) control store.
These hardware-level instructions move data throughout the data path.
The micro-instruction cycle begins when the microsequencer uses its microprogram counter to fetch the next machine instruction from random-access memory. The next step is to decode the machine instruction by selecting the proper output line to the hardware module.
The final step is to execute the instruction using the hardware module's set of gates.
Instructions to perform arithmetic are passed through an arithmetic logic unit (ALU). The ALU has circuits to perfo
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ic logic unit (ALU). The ALU has circuits to perform elementary operations to add, shift, and compare integers. By combining and looping the elementary operations through the ALU, the CPU performs its complex arithmetic.
Microcode instructions move data between the CPU and the memory controller. Memory controller microcode instructions manipulate two registers. The memory address register is used to access each memory cell's address. The memory data register is used to set and read each cell's contents.
Microcode instructions move data between the CPU and the many computer buses. The disk controller bus writes to and reads from hard disk drives. Data is also moved between the CPU and other functional units via the peripheral component interconnect express bus.
== Notes ==
== References ==
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The terms local programme, local programming, local content or local television refers to a television program made by a television station or independent television producer for broadcast only within the station's transmission area or television market. Local programmes can encompass the whole range of programme genres but will usually only cover subjects or people of particular interest to an audience within the station's coverage area.
For example, a local sports programme will present results, interviews and coverage of games or matches, just like a network sports programme, but it would only feature teams and players from within the broadcaster's transmission area.
In some cases a television network programme may include a local element as well. This is particularly the case in the United Kingdom and still happens today with Politics Show. The BBC regions will all opt-out at the same time from the main programme to present a locally produced segment.
Sometimes locally made progr
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lly produced segment.
Sometimes locally made programmes that are not too specific to the transmission area, will be sold to other local stations for broadcast in their region.
Historically there was a large percentage of local programming on television. Late in the 20th century this has significantly fallen. In many cases the only local programmes on a television station today will be the local newscast.
The above can also apply to radio. A national radio network may have local studios or affiliates who opt-out at various times to present local programs and content.
In the late-1950s, many of the early Australian television series such as Melbourne Magazine (1957), Sydney Tonight (1956–1959), and TV Talent Scout (1957–1958) were broadcast in only a single city.
== Canada ==
In Canada, historically local television stations produced a significant volume of local programming, including newscasts, locally or regionally oriented talk shows, and variety entertainment programs such as Ti
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ows, and variety entertainment programs such as Tiny Talent Time or Homegrown Cafe; a few stations, such as CHCH-TV in Hamilton, Ontario and CJOH in Ottawa, also distributed some of their local programming more widely through television syndication, most notably CHCH's Hilarious House of Frightenstein and CJOH's You Can't Do That on Television, both of which were broadcast across both Canada and the United States.
With the cross-national consolidation of Canadian media ownership in the 1990s and 2000s, network-affiliated stations now rarely produce much more than their own local or regional newscasts, although some stations may continue to produce a small amount of additional local programming. Independent stations may produce more local programming, although such stations are now rare in the Canadian media landscape.
In radio, virtually all Canadian commercial radio stations are officially programmed locally, although many stations cut costs by contracting some dayparts out to voice-t
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costs by contracting some dayparts out to voice-tracked hosts who are not actually located in the station's physical studio or even necessarily in the same city, using a home studio, and may even be performing their show from the United States. The CBC Radio One, CBC Radio 2, Ici Radio-Canada Première and Ici Musique networks consist primarily of networked national programming, although all include some degree of local programming in certain time blocks. Radio One and Première stations have a significant number of production centres which create and air their own local morning and/or afternoon talk shows, while Radio 2's and Ici Musique's local content is limited to local news and weather updates.
== United States ==
The term is also generally accepted to refer to television programming that is not produced by a broadcast or other media source for national or international distribution (broadcast syndication). Usually programming of local interest is produced by either a Public, ed
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local interest is produced by either a Public, educational, and government access (PEG) television organization, cable TV operator or broadcast network affiliate stations that offer local radio news and television news.
=== Placeholder use of term ===
Additionally, the term is used in a more generic form in the United States, Canada, Mexico and other countries in the Western Hemisphere as a placeholder term within published national program guide listings in publications such as the post-2006 format TV Guide or USA Today which only carry the default schedules of national networks, where the "local programming" designation replaces detailed listings for a local station that would be impossible to print in a national publication. Outside of local newscasts and some rare non-news programming however, the term merely describes time periods under a local station's control, where syndicated content airs rather than true local programming. For equivalent electronic program guide listings f
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For equivalent electronic program guide listings for set-top boxes, the term is used mainly with PEG stations and networks which do not have a schedule compiled by a cable operator as a default placeholder; other instances are with only broadcast stations who outright refuse or do not release their program listings due to lack of staff, though as advertisers usually demand a minimum schedule to place their ads on a television station (and most of these stations are associated with smaller national digital subchannel networks which do provide a default schedule for distribution), the vast majority of broadcast stations do provide program listings. Wikipedia itself also uses this designation in its series of American network television schedule articles for non-network programming time.
== United Kingdom ==
Many local television stations in the United Kingdom ceased broadcasting due to a lack of viability, but some stations are still being broadcast, including:
Midlands Asian Televis
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eing broadcast, including:
Midlands Asian Television (MATV)
NVTV (Northern Visions Television), Belfast
That's TV
== See also ==
Advertorial, a common form of local programming in North America where local businesses advertise their products and services
List of local children's television series (United States)
Local television in Greece
Local origination (disambiguation)
Network affiliate
Regional television in Australia
Regional variation
== References ==
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An integer programming problem is a mathematical optimization or feasibility program in which some or all of the variables are restricted to be integers. In many settings the term refers to integer linear programming (ILP), in which the objective function and the constraints (other than the integer constraints) are linear.
Integer programming is NP-complete. In particular, the special case of 0–1 integer linear programming, in which unknowns are binary, and only the restrictions must be satisfied, is one of Karp's 21 NP-complete problems.
If some decision variables are not discrete, the problem is known as a mixed-integer programming problem.
== Canonical and standard form for ILPs ==
In integer linear programming, the canonical form is distinct from the standard form. An integer linear program in canonical form is expressed thus (note that it is the
x
{\displaystyle \mathbf {x} }
vector which is to be decided):
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{x} }
vector which is to be decided):
maximize
x
∈
Z
n
c
T
x
subject to
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subject to
A
x
≤
b
,
x
≥
0
{\displaystyle {\begin{aligned}&{\underset {\mathbf {x} \in \mathbb {Z} ^{n}}{\text{maximize}}}&&\mathbf {c} ^{\mathrm {T} }\mathbf {x} \\&{\text{subject to}}&&A\mathbf {x} \leq \mathbf {b} ,\\&&&\mathbf {x} \geq \mathbf {0} \end{aligned}}}
and an ILP in standard form is expressed as
maximize
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maximize
x
∈
Z
n
c
T
x
subject to
A
x
+
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+
s
=
b
,
s
≥
0
,
x
≥
0
,
{\displaystyle {\begin{aligned}&{\underset {\mathbf {x} \in \mathbb {Z} ^{n}}{\text{maximize}}}&&\mathbf {c} ^{\mathrm {T} }\mathbf {x} \\&{\text{subject to}}&&A\mathbf {x} +\mathbf {s} =\mathbf {b} ,\\&&&\mathbf {s} \geq \mathbf {0} ,\\&&&\mathbf {x} \geq \mathbf {0} ,\end{aligned}}}
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\&&&\mathbf {x} \geq \mathbf {0} ,\end{aligned}}}
where
c
∈
R
n
,
b
∈
R
m
{\displaystyle \mathbf {c} \in \mathbb {R} ^{n},\mathbf {b} \in \mathbb {R} ^{m}}
are vectors and
A
∈
R
m
×
n
{\displaystyle A\in \mathbb {R} ^{m\times n}}
is a matrix. As with linear programs, ILPs not in standard form can be converted to standard form by eliminating inequalities, introducing slack variables (
s
{\displaystyle \mathbf {s} }
) and replacing variables that are not sign-constrained with the
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variables that are not sign-constrained with the difference of two sign-constrained variables.
== Example ==
The plot on the right shows the following problem.
maximize
x
,
y
∈
Z
y
subject to
−
x
+
y
≤
1
3
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