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Modular programming is a
software design Software design is the process by which an agent creates a specification of a software artifact intended to accomplish goals, using a set of primitive components and subject to constraints. Software design may refer to either "all the activity ...
technique that emphasizes separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality. A module
interface Interface or interfacing may refer to: Academic journals * ''Interface'' (journal), by the Electrochemical Society * '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics'' * '' Int ...
expresses the elements that are provided and required by the module. The elements defined in the interface are detectable by other modules. The
implementation Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy. Industry-specific definitions Computer science In computer science, an implementation is a real ...
contains the working code that corresponds to the elements declared in the interface. Modular programming is closely related to
structured programming Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of selection ( if/then/else) and repetition (w ...
and
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
, all having the same goal of facilitating construction of large software programs and systems by
decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...
into smaller pieces, and all originating around the 1960s. While the historical usage of these terms has been inconsistent, "modular programming" now refers to the high-level decomposition of the code of an entire program into pieces: structured programming to the low-level code use of structured
control flow In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an '' ...
, and object-oriented programming to the ''data'' use of objects, a kind of
data structure In computer science, a data structure is a data organization, management, and storage format that is usually chosen for Efficiency, efficient Data access, access to data. More precisely, a data structure is a collection of data values, the rel ...
. In object-oriented programming, the use of interfaces as an architectural pattern to construct modules is known as
interface-based programming Interface-based programming, also known as interface-based architecture, is an architectural pattern for implementing modular programming at the component level in an object-oriented programming language which does not have a module system. An ...
.


History

Modular programming, in the form of subsystems (particularly for I/O) and software libraries, dates to early software systems, where it was used for code reuse. Modular programming per se, with a goal of modularity, developed in the late 1960s and 1970s, as a larger-scale analog of the concept of
structured programming Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of selection ( if/then/else) and repetition (w ...
(1960s). The term "modular programming" dates at least to the National Symposium on Modular Programming, organized at the Information and Systems Institute in July 1968 by Larry Constantine; other key concepts were
information hiding In computer science, information hiding is the principle of segregation of the ''design decisions'' in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decisio ...
(1972) and separation of concerns (SoC, 1974). Modules were not included in the original specification for
ALGOL 68 ALGOL 68 (short for ''Algorithmic Language 1968'') is an imperative programming language that was conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and more rigorously ...
(1968), but were included as extensions in early implementations, ALGOL 68-R (1970) and ALGOL 68C (1970), and later formalized. One of the first languages designed from the start for modular programming was the short-lived
Modula The Modula programming language is a descendant of the Pascal language. It was developed in Switzerland, at ETH Zurich, in the mid-1970s by Niklaus Wirth, the same person who designed Pascal. The main innovation of Modula over Pascal is a m ...
(1975), by Niklaus Wirth. Another early modular language was Mesa (1970s), by Xerox PARC, and Wirth drew on Mesa as well as the original Modula in its successor,
Modula-2 Modula-2 is a structured, procedural programming language developed between 1977 and 1985/8 by Niklaus Wirth at ETH Zurich. It was created as the language for the operating system and application software of the Lilith personal workstation. It w ...
(1978), which influenced later languages, particularly through its successor, Modula-3 (1980s). Modula's use of dot- qualified names, like M.a to refer to object a from module M, coincides with notation to access a field of a record (and similarly for attributes or methods of objects), and is now widespread, seen in C#, Dart, Go, Java, OCaml, and Python, among others. Modular programming became widespread from the 1980s: the original Pascal language (1970) did not include modules, but later versions, notably UCSD Pascal (1978) and
Turbo Pascal Turbo Pascal is a software development system that includes a compiler and an integrated development environment (IDE) for the Pascal programming language running on CP/M, CP/M-86, and DOS. It was originally developed by Anders Hejlsberg at ...
(1983) included them in the form of "units", as did the Pascal-influenced Ada (1980). The Extended Pascal ISO 10206:1990 standard kept closer to Modula2 in its modular support. Standard ML (1984) has one of the most complete module systems, including
functors In mathematics, specifically category theory, a functor is a mapping between categories. Functors were first considered in algebraic topology, where algebraic objects (such as the fundamental group) are associated to topological spaces, and ma ...
(parameterized modules) to map between modules. In the 1980s and 1990s, modular programming was overshadowed by and often conflated with
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
, particularly due to the popularity of C++ and Java. For example, the C family of languages had support for objects and classes in C++ (originally
C with Classes C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded signific ...
, 1980) and Objective-C (1983), only supporting modules 30 years or more later. Java (1995) supports modules in the form of packages, though the primary unit of code organization is a class. However, Python (1991) prominently used both modules and objects from the start, using modules as the primary unit of code organization and "packages" as a larger-scale unit; and Perl 5 (1994) includes support for both modules and objects, with a vast array of modules being available from CPAN (1993).
OCaml OCaml ( , formerly Objective Caml) is a general-purpose, multi-paradigm programming language which extends the Caml dialect of ML with object-oriented features. OCaml was created in 1996 by Xavier Leroy, Jérôme Vouillon, Damien Doligez, D ...
(1996) followed ML by supporting modules and functors. Modular programming is now widespread, and found in virtually all major languages developed since the 1990s. The relative importance of modules varies between languages, and in class-based object-oriented languages there is still overlap and confusion with classes as a unit of organization and encapsulation, but these are both well-established as distinct concepts.


Terminology

The term
assembly Assembly may refer to: Organisations and meetings * Deliberative assembly, a gathering of members who use parliamentary procedure for making decisions * General assembly, an official meeting of the members of an organization or of their representa ...
(as in
.NET languages CLI languages are computer programming languages that are used to produce libraries and programs that conform to the Common Language Infrastructure (CLI) specifications. With some notable exceptions, most CLI languages compile entirely to the Com ...
like C#, F# or Visual Basic .NET) or package (as in
Dart Dart or DART may refer to: * Dart, the equipment in the game of darts Arts, entertainment and media * Dart (comics), an Image Comics superhero * Dart, a character from ''G.I. Joe'' * Dart, a ''Thomas & Friends'' railway engine character * D ...
, Go or
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
) is sometimes used instead of module. In other implementations, these are distinct concepts; in Python a package is a collection of modules, while in Java 9 the introduction of the new module concept (a collection of packages with enhanced access control) was implemented. Furthermore, the term "package" has other uses in software (for example .NET NuGet packages). A component is a similar concept, but typically refers to a higher level; a component is a piece of a whole system, while a module is a piece of an individual program. The scale of the term "module" varies significantly between languages; in Python it is very small-scale and each file is a module, while in Java 9 it is planned to be large-scale, where a module is a collection of packages, which are in turn collections of files. Other terms for modules include unit, used in Pascal dialects.


Language support

Languages that formally support the module concept include Ada,
Algol ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by th ...
,
BlitzMax Blitz BASIC is the programming language dialect of the first Blitz compilers, devised by New Zealand-based developer Mark Sibly. Being derived from BASIC, Blitz syntax was designed to be easy to pick up for beginners first learning to program. T ...
, C++, C#, Clojure,
COBOL COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily ...
,
Common_Lisp Common Lisp (CL) is a dialect of the Lisp programming language, published in ANSI standard document ''ANSI INCITS 226-1994 (S20018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperlinked HTML version, has been derived fr ...
, D,
Dart Dart or DART may refer to: * Dart, the equipment in the game of darts Arts, entertainment and media * Dart (comics), an Image Comics superhero * Dart, a character from ''G.I. Joe'' * Dart, a ''Thomas & Friends'' railway engine character * D ...
, eC, Erlang, Elixir, Elm, F, F#, Fortran, Go, Haskell, IBM/360 Assembler, Control Language (CL),
IBM RPG RPG is a high-level programming language for business applications, introduced in 1959 for the IBM 1401. It is most well known as the primary programming language of IBM's midrange computer product line, including the IBM i operating system. ...
,
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
, Julia,
MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementa ...
, ML,
Modula The Modula programming language is a descendant of the Pascal language. It was developed in Switzerland, at ETH Zurich, in the mid-1970s by Niklaus Wirth, the same person who designed Pascal. The main innovation of Modula over Pascal is a m ...
,
Modula-2 Modula-2 is a structured, procedural programming language developed between 1977 and 1985/8 by Niklaus Wirth at ETH Zurich. It was created as the language for the operating system and application software of the Lilith personal workstation. It w ...
, Modula-3, Morpho, NEWP,
Oberon Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fair ...
, Oberon-2,
Objective-C Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its N ...
,
OCaml OCaml ( , formerly Objective Caml) is a general-purpose, multi-paradigm programming language which extends the Caml dialect of ML with object-oriented features. OCaml was created in 1996 by Xavier Leroy, Jérôme Vouillon, Damien Doligez, D ...
, several derivatives of Pascal ( Component Pascal, Object Pascal,
Turbo Pascal Turbo Pascal is a software development system that includes a compiler and an integrated development environment (IDE) for the Pascal programming language running on CP/M, CP/M-86, and DOS. It was originally developed by Anders Hejlsberg at ...
, UCSD Pascal),
Perl Perl is a family of two High-level programming language, high-level, General-purpose programming language, general-purpose, Interpreter (computing), interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it ...
,
PHP PHP is a General-purpose programming language, general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementati ...
,
PL/I PL/I (Programming Language One, pronounced and sometimes written PL/1) is a procedural, imperative computer programming language developed and published by IBM. It is designed for scientific, engineering, business and system programming. It ...
, PureBasic, Python, R,
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapp ...
,
Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), ...
,
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of Website, websites use JavaScript on the Client (computing), client side ...
, Visual Basic .NET and WebDNA. Conspicuous examples of languages that lack support for modules are C and have been C++ and Pascal in their original form, C and C++ do, however, allow separate compilation and declarative interfaces to be specified using header files. Modules were added to Objective-C in iOS 7 (2013); to C++ with C++20, and Pascal was superseded by
Modula The Modula programming language is a descendant of the Pascal language. It was developed in Switzerland, at ETH Zurich, in the mid-1970s by Niklaus Wirth, the same person who designed Pascal. The main innovation of Modula over Pascal is a m ...
and
Oberon Oberon () is a king of the fairies in medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania, Queen of the Fair ...
, which included modules from the start, and various derivatives that included modules.
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of Website, websites use JavaScript on the Client (computing), client side ...
has had native modules since
ECMAScript ECMAScript (; ES) is a JavaScript standard intended to ensure the interoperability of web pages across different browsers. It is standardized by Ecma International in the documenECMA-262 ECMAScript is commonly used for client-side scriptin ...
2015. Modular programming can be performed even where the programming language lacks explicit syntactic features to support named modules, like, for example, in C. This is done by using existing language features, together with, for example, coding conventions, programming idioms and the physical code structure. IBM i also uses modules when programming in the
Integrated Language Environment The Integrated Language Environment (ILE) is a programming model developed by IBM for their AS/400 line of computers and remains an important part of the IBM i programming environment. Languages IBM provides ILE compilers for C, C++, RPG, COBOL ...
(ILE).


Key aspects

With modular programming, concerns are separated such that modules perform logically discrete functions, interacting through well-defined interfaces. Often modules form a
directed acyclic graph In mathematics, particularly graph theory, and computer science, a directed acyclic graph (DAG) is a directed graph with no directed cycles. That is, it consists of vertices and edges (also called ''arcs''), with each edge directed from one v ...
(DAG); in this case a cyclic dependency between modules is seen as indicating that these should be a single module. In the case where modules do form a DAG they can be arranged as a hierarchy, where the lowest-level modules are independent, depending on no other modules, and higher-level modules depend on lower-level ones. A particular program or library is a top-level module of its own hierarchy, but can in turn be seen as a lower-level module of a higher-level program, library, or system. When creating a modular system, instead of creating a monolithic application (where the smallest component is the whole), several smaller modules are written separately so when they are composed together, they construct the executable application program. Typically these are also compiled separately, via
separate compilation Separate or separates may refer to: *Soil separates, three kinds of soil mineral particles: sand, silt, and clay *Separate (song), 2016 song by South African songstress Amanda Black *Separates (clothing), Mix-and-match separates, clothing * ''Sep ...
, and then linked by a linker. A just-in-time compiler may perform some of this construction "on-the-fly" at run time. These independent functions are commonly classified as either program control functions or specific task functions. Program control functions are designed to work for one program. Specific task functions are closely prepared to be applicable for various programs. This makes modular designed systems, if built correctly, far more reusable than a traditional monolithic design, since all (or many) of these modules may then be reused (without change) in other projects. This also facilitates the "breaking down" of projects into several smaller projects. Theoretically, a modularized software project will be more easily assembled by large teams, since no team members are creating the whole system, or even need to know about the system as a whole. They can focus just on the assigned smaller task.


See also

* Architecture description language * Cohesion (computer science) * Component-based software engineering * Conway's law * Coupling (computer science) * David Parnas *
Information hiding In computer science, information hiding is the principle of segregation of the ''design decisions'' in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decisio ...
(encapsulation) *
Library (computing) In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and su ...
* List of system quality attributes * Modular design *
Plug-in (computing) In computing, a plug-in (or plugin, add-in, addin, add-on, or addon) is a software component that adds a specific feature to an existing computer program. When a program supports plug-ins, it enables customization. A theme or skin is a prese ...
* Snippet (programming) * Structured Analysis *
Structured programming Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of selection ( if/then/else) and repetition (w ...


Notes


References


External links


How To Decompose a System into Modules

SMC Platform
{{DEFAULTSORT:Modular Programming Programming paradigms Programming