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Modular programming is a software design technique that emphasizes separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect or "concern" of the desired functionality.
A module interface expresses the elements that are provided and required by the module. The elements defined in the interface are detectable by other modules. The implementation contains the working code that corresponds to the elements declared in the interface. Modular programming is closely related to structured programming and object-oriented programming, all having the same goal of facilitating construction of large software programs and systems by decomposition 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, and object-oriented programming to the data use of objects, a kind of data structure.
In object-oriented programming, the use of interfaces as an architectural pattern to construct modules is known as interface-based programming.[citation needed]
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 (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 (1972) and separation of concerns (SoC, 1974).
Modules were not included in the original specification for ALGOL 68 (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 (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 (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++, 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 (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 (parameterized modules) to map between modules.
In the 1980s and 1990s, modular programming was overshadowed by and often conflated with object-oriented programming, 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, 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 (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 (as in .NET languages like C#, F# or Visual Basic .NET) or package (as in Dart, Go or Java) 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, BlitzMax, C++, C#, Clojure, COBOL, Common Lisp, D, Dart, eC, Erlang, Elixir, Elm, F, F#, Fortran, Go, Haskell, IBM/360 Assembler, Control Language (CL), IBM RPG, Java,Julia, MATLAB, ML, Modula, Modula-2, Modula-3, Morpho, NEWP, Oberon, Oberon-2, Objective-C, OCaml, several Pascal derivatives (Component Pascal, Object Pascal, Turbo Pascal, UCSD Pascal), Perl, PHP, PL/I, PureBasic, Python, R, Ruby,Rust, JavaScript,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 and Oberon, which included modules from the start, and various derivatives that included modules. JavaScript has had native modules since ECMAScript 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 (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 (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 , 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 – Standardized language on architecture description
- Cohesion (computer science) – Degree to which elements within a module belong together
- Component-based software engineering – Engineering focused on building software from reusable components
- Conway's law – Adage linking organization and system structure
- Coupling (computer science) – Degree of interdependence between software modules
- David Parnas – Canadian software engineer
- Information hiding – Principle of computer program design (encapsulation)
- Library (computing) – Collection of resources used to develop a computer program
- List of system quality attributes – Non-functional requirements for system evaluation
- Modular design – Design approach
- Plug-in (computing) – Software component that extends the functionality of existing software
- Snippet (programming) – Small region of re-usable source code, machine code, or text
- Structured Analysis – method for analyzing and converting business requirements of a project into functional specifications for its conception, its implementation and its monitoring
- Structured programming – Programming paradigm based on control flow
Notes
- The term "package" is used for the analog of modules in the JLS; — see Java package. "Modules", a kind of collection of packages, are planned for Java 9 as part of Project Jigsaw; these were earlier called "superpackages" and planned for Java 7.
References
- Lindsey, Charles H. (Feb 1976). "Proposal for a Modules Facility in ALGOL 68" (PDF). ALGOL Bulletin (39): 20–29. Archived from the original (PDF) on 2016-03-03. Retrieved 2014-12-01.
- David MacQueen (August 1984). "Modules for Standard ML". LFP '84 Proceedings of the 1984 ACM Symposium on LISP and functional programming. pp. 198–207. doi:10.1145/800055.802036.
- James Gosling, Bill Joy, Guy Steele, Gilad Bracha, The Java Language Specification, Third Edition, ISBN 0-321-24678-0, 2005. In the Introduction, it is stated "Chapter 7 describes the structure of a program, which is organized into packages similar to the modules of Modula." The word "module" has no special meaning in Java.
- "Class: Module (Ruby 2.0.0)".
- ECMAScript® 2015 Language Specification, 15.2 Modules
- "N4720: Working Draft, Extensions to C++ for Modules" (PDF).
External links
- How To Decompose a System into Modules
- SMC Platform
This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Modular programming news newspapers books scholar JSTOR June 2022 Learn how and when to remove this message Modular programming is a software design technique that emphasizes separating the functionality of a program into independent interchangeable modules such that each contains everything necessary to execute only one aspect or concern of the desired functionality A module interface expresses the elements that are provided and required by the module The elements defined in the interface are detectable by other modules The implementation contains the working code that corresponds to the elements declared in the interface Modular programming is closely related to structured programming and object oriented programming all having the same goal of facilitating construction of large software programs and systems by decomposition 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 and object oriented programming to the data use of objects a kind of data structure In object oriented programming the use of interfaces as an architectural pattern to construct modules is known as interface based programming citation needed HistoryModular 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 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 1972 and separation of concerns SoC 1974 Modules were not included in the original specification for ALGOL 68 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 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 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 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 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 parameterized modules to map between modules In the 1980s and 1990s modular programming was overshadowed by and often conflated with object oriented programming 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 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 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 TerminologyThe term assembly as in NET languages like C F or Visual Basic NET or package as in Dart Go or Java 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 supportLanguages that formally support the module concept include Ada ALGOL BlitzMax C C Clojure COBOL Common Lisp D Dart eC Erlang Elixir Elm F F Fortran Go Haskell IBM 360 Assembler Control Language CL IBM RPG Java Julia MATLAB ML Modula Modula 2 Modula 3 Morpho NEWP Oberon Oberon 2 Objective C OCaml several Pascal derivatives Component Pascal Object Pascal Turbo Pascal UCSD Pascal Perl PHP PL I PureBasic Python R Ruby Rust JavaScript 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 and Oberon which included modules from the start and various derivatives that included modules JavaScript has had native modules since ECMAScript 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 ILE Key aspectsWith modular programming concerns are separated such that modules perform logically discrete functions interacting through well defined interfaces Often modules form a directed acyclic graph 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 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 alsoArchitecture description language Standardized language on architecture description Cohesion computer science Degree to which elements within a module belong together Component based software engineering Engineering focused on building software from reusable components Conway s law Adage linking organization and system structure Coupling computer science Degree of interdependence between software modulesPages displaying short descriptions of redirect targets David Parnas Canadian software engineer Information hiding Principle of computer program design encapsulation Library computing Collection of resources used to develop a computer program List of system quality attributes Non functional requirements for system evaluation Modular design Design approach Plug in computing Software component that extends the functionality of existing software Snippet programming Small region of re usable source code machine code or text Structured Analysis method for analyzing and converting business requirements of a project into functional specifications for its conception its implementation and its monitoringPages displaying wikidata descriptions as a fallback Structured programming Programming paradigm based on control flowNotesThe term package is used for the analog of modules in the JLS see Java package Modules a kind of collection of packages are planned for Java 9 as part of Project Jigsaw these were earlier called superpackages and planned for Java 7 ReferencesLindsey Charles H Feb 1976 Proposal for a Modules Facility in ALGOL 68 PDF ALGOL Bulletin 39 20 29 Archived from the original PDF on 2016 03 03 Retrieved 2014 12 01 David MacQueen August 1984 Modules for Standard ML LFP 84 Proceedings of the 1984 ACM Symposium on LISP and functional programming pp 198 207 doi 10 1145 800055 802036 James Gosling Bill Joy Guy Steele Gilad Bracha The Java Language Specification Third Edition ISBN 0 321 24678 0 2005 In the Introduction it is stated Chapter 7 describes the structure of a program which is organized into packages similar to the modules of Modula The word module has no special meaning in Java Class Module Ruby 2 0 0 ECMAScript 2015 Language Specification 15 2 Modules N4720 Working Draft Extensions to C for Modules PDF External linksHow To Decompose a System into Modules SMC Platform
