Modularity (programming)
Encyclopedia
Modular programming is a software design technique that increases the extent to which software is composed of separate, interchangeable components called modules by breaking down program functions into modules, each of which accomplishes one function and contains everything necessary to accomplish this. Conceptually, modules represent a separation of concerns
, and improve maintainability
by enforcing logical boundaries between components. Modules are typically incorporated into the program through interfaces
. 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.
, BlitzMax, COBOL
, Component Pascal
, D
, Erlang, F, Fortran
, Haskell
, IBM/360 Assembler, IBM RPG, Java
(packages are considered modules in the JLS), MATLAB
, ML, Modula-2
, Modula-3
, Morpho, Oberon
, OCaml, Pascal
, Perl
, PL/1, Python
, and Ruby
. The IBM System i
also uses Modules in CL
, COBOL
, and RPG when programming in the Integrated Language Environment (ILE). Modular programming can be performed even where the programming language lacks explicit syntactic features to support named modules.
Software tools can create modular code units from groups of components. Libraries of components built from separately compiled modules can be combined into a whole by using a linker.
such that no (or few) modules depend upon other modules of the system. To have as few dependencies as possible is the goal.
When creating a modular system, instead of creating a monolithic application (where the smallest component is the whole), several smaller modules are built (and usually compiled) separately so that, when composed together, they construct the executable application program. A just in time compiler
may perform some of this construction "on-the-fly" at run time.
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 (through "divide and conquer
") 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 (this, it is claimed, counters the key assumption of The Mythical Man Month – making it actually possible to add more developers to a late software project – without making it later still).
has, more recently, gained ground over the earlier, more conventional, "
or Object-oriented programming
starts in this context is subjective. It might be defined as the natural predecessor of OOP
, or an evolutionary step beyond it - depending upon viewpoint.
Separation of concerns
In computer science, separation of concerns is the process of separating a computer program into distinct features that overlap in functionality as little as possible. A concern is any piece of interest or focus in a program. Typically, concerns are synonymous with features or behaviors...
, and improve maintainability
Maintainability
In engineering, maintainability is the ease with which a product can be maintained in order to:* isolate defects or their cause* correct defects or their cause* meet new requirements* make future maintenance easier, or* cope with a changed environment...
by enforcing logical boundaries between components. Modules are typically incorporated into the program through interfaces
Interface (computer science)
In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...
. 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
Implementation
Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy.-Computer Science:...
contains the working code that corresponds to the elements declared in the interface.
Language support
Languages that formally support the module concept include AdaAda (programming language)
Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages...
, BlitzMax, COBOL
COBOL
COBOL is one of the oldest programming languages. Its name is an acronym for COmmon Business-Oriented Language, defining its primary domain in business, finance, and administrative systems for companies and governments....
, Component Pascal
Component Pascal
Component Pascal is a programming language in the tradition of Niklaus Wirth's Pascal, Modula-2, Oberon and Oberon-2. It bears the name of the Pascal programming language but is incompatible with it. Instead, it is a minor variant and refinement of Oberon-2, designed and supported by a small ETH...
, D
D (programming language)
The D programming language is an object-oriented, imperative, multi-paradigm, system programming language created by Walter Bright of Digital Mars. It originated as a re-engineering of C++, but even though it is mainly influenced by that language, it is not a variant of C++...
, Erlang, F, Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
, Haskell
Haskell (programming language)
Haskell is a standardized, general-purpose purely functional programming language, with non-strict semantics and strong static typing. It is named after logician Haskell Curry. In Haskell, "a function is a first-class citizen" of the programming language. As a functional programming language, the...
, IBM/360 Assembler, IBM RPG, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
(packages are considered modules in the JLS), MATLAB
MATLAB
MATLAB is a numerical computing environment and fourth-generation programming language. Developed by MathWorks, MATLAB allows matrix manipulations, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs written in other languages,...
, ML, Modula-2
Modula-2
Modula-2 is a computer programming language designed and developed between 1977 and 1980 by Niklaus Wirth at ETH Zurich as a revision of Pascal to serve as the sole programming language for the operating system and application software for the personal workstation Lilith...
, Modula-3
Modula-3
In computer science, Modula-3 is a programming language conceived as a successor to an upgraded version of Modula-2 known as Modula-2+. While it has been influential in research circles it has not been adopted widely in industry...
, Morpho, Oberon
Oberon (programming language)
Oberon is a programming language created in 1986 by Professor Niklaus Wirth and his associates at ETH Zurich in Switzerland. It was developed as part of the implementation of the Oberon operating system...
, OCaml, Pascal
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
, Perl
Perl
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
, PL/1, Python
Python (programming language)
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
, and Ruby
Ruby (programming language)
Ruby is a dynamic, reflective, general-purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto...
. The IBM System i
IBM System i
The IBM System i is IBM's previous generation of midrange computer systems for IBM i users, and was subsequently replaced by the IBM Power Systems in April 2008....
also uses Modules in CL
AS/400 Control Language
The AS/400 Control Language is a scripting language for the IBM AS/400 midrange platform bearing a resemblance to the IBM Job Control Language and consisting of an ever expanding set of command objects used to invoke traditional AS/400 programs and/or get help on what those programs do...
, COBOL
COBOL
COBOL is one of the oldest programming languages. Its name is an acronym for COmmon Business-Oriented Language, defining its primary domain in business, finance, and administrative systems for companies and governments....
, and RPG when programming in the Integrated Language Environment (ILE). Modular programming can be performed even where the programming language lacks explicit syntactic features to support named modules.
Software tools can create modular code units from groups of components. Libraries of components built from separately compiled modules can be combined into a whole by using a linker.
Key aspects
With modular programming, concerns are separatedSeparation of concerns
In computer science, separation of concerns is the process of separating a computer program into distinct features that overlap in functionality as little as possible. A concern is any piece of interest or focus in a program. Typically, concerns are synonymous with features or behaviors...
such that no (or few) modules depend upon other modules of the system. To have as few dependencies as possible is the goal.
When creating a modular system, instead of creating a monolithic application (where the smallest component is the whole), several smaller modules are built (and usually compiled) separately so that, when composed together, they construct the executable application program. A just in time compiler
Just-in-time compilation
In computing, just-in-time compilation , also known as dynamic translation, is a method to improve the runtime performance of computer programs. Historically, computer programs had two modes of runtime operation, either interpreted or static compilation...
may perform some of this construction "on-the-fly" at run time.
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 (through "divide and conquer
Divide and conquer
Divide and conquer may refer to:* Divide and rule, in politics, sociology and economics, a strategy to gain or maintain power...
") 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 (this, it is claimed, counters the key assumption of The Mythical Man Month – making it actually possible to add more developers to a late software project – without making it later still).
Implementation
Message passingMessage passing
Message passing in computer science is a form of communication used in parallel computing, object-oriented programming, and interprocess communication. In this model, processes or objects can send and receive messages to other processes...
has, more recently, gained ground over the earlier, more conventional, "
Call" interfaces, becoming the more dominant linkage between separate modules as an attempt to solve the "versioning problem" (sometimes experienced when using interfaces for communication between the modules).History
Traditional programming languages have been used to support modular programming - since at least the 1960s. Modular programming is a loosely defined concept with no official definition. It is, in essence, simply a programming technique. Exactly where modularized programming ends, and Dynamically Linked LibrariesDynamic-link library
Dynamic-link library , or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems...
or Object-oriented programming
Object-oriented programming
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
starts in this context is subjective. It might be defined as the natural predecessor of OOP
Object-oriented programming
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
, or an evolutionary step beyond it - depending upon viewpoint.
See also
- Architecture description languageArchitecture description languageDifferent communities use the term architecture description language. Some important communities are the system engineering community, the software engineering community and the enterprise modelling and engineering community...
- CohesionCohesion (computer science)In computer programming, cohesion is a measure of how strongly-related each piece of functionality expressed by the source code of a software module is...
- Constructionist design methodologyConstructionist design methodologyThe Constructionist Design Methodology was developed by artificial intelligence researcher Kristinn R. Thórisson and his students at Columbia University and Reykjavik University for use in the development of cognitive robotics, communicative humanoids and broad AI systems...
, a methodology for creating modular, broad Artificial Intelligence systems - Component-based software engineeringComponent-based software engineeringComponent-based software engineering is a branch of software engineering that emphasizes the separation of concerns in respect of the wide-ranging functionality available throughout a given software system...
- CouplingCoupling (computer science)In computer science, coupling or dependency is the degree to which each program module relies on each one of the other modules.Coupling is usually contrasted with cohesion. Low coupling often correlates with high cohesion, and vice versa...
- David ParnasDavid ParnasDavid Lorge Parnas is a Canadian early pioneer of software engineering, who developed the concept of information hiding in modular programming, which is an important element of object-oriented programming today. He is also noted for his advocacy of precise documentation.- Biography :Parnas earned...
- Information hidingInformation hidingIn 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 decision is changed...
(encapsulation) - Library (computing)
- List of system quality attributes
- Snippet (programming)Snippet (programming)Snippet is a programming term for a small region of re-usable source code, machine code or text. Ordinarily, these are formally-defined operative units to incorporate into larger programming modules...
- Structured programmingStructured programmingStructured programming is a programming paradigm aimed on improving the clarity, quality, and development time of a computer program by making extensive use of subroutines, block structures and for and while loops - in contrast to using simple tests and jumps such as the goto statement which could...