A software component is a modular unit of

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

that encapsulates specific functionality. The desired characteristics of a component are

reusability In computer programming, reusability describes the quality of a software asset that affects its ability to be used in a software system for which it was ''not'' specifically designed. An asset that is easy to reuse and provides utility is conside ...

and

maintainability Maintainability is the ease of maintaining or providing maintenance for a functioning product or service. Depending on the field, it can have slightly different meanings. Usage in different fields Engineering In engineering, maintainability ...

Value

Components allow

software development Software development is the process of designing and Implementation, implementing a software solution to Computer user satisfaction, satisfy a User (computing), user. The process is more encompassing than Computer programming, programming, wri ...

to assemble software with reliable parts rather than writing

code In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communicati ...

for every aspect; allowing for

implementation Implementation is the realization of an application, execution of a plan, idea, scientific modelling, model, design, specification, Standardization, standard, algorithm, policy, or the Management, administration or management of a process or Goal ...

to be more like factory assembly than custom building.

Attributes

Desirable attributes of a component include but are not limited to: * Cohesive encapsulates related functionality * Reusable *

Robust Robustness is the property of being strong and healthy in constitution. When it is transposed into a system, it refers to the ability of tolerating perturbations that might affect the system's functional body. In the same line ''robustness'' can ...

* ''Substitutable'' can be replaced by another component with the same interface *

Documented A document is a written, drawn, presented, or memorialized representation of thought, often the manifestation of non-fictional, as well as fictional, content. The word originates from the Latin ', which denotes a "teaching" or "lesson": t ...

Tested ''Tested'' is the first official live album by punk rock band Bad Religion. It was recorded in the USA, Canada, Germany, Estonia, Denmark, Italy and Austria, in 1996, and released in 1997. It is Bad Religion's second live album. Instead of usi ...

Third-party

Some components are built in-house by the same organization or team building the

software system A software system is a system of intercommunicating software component, components based on software forming part of a computer system (a combination of Computer hardware, hardware and software). It "consists of a number of separate Computer progr ...

. Some are

third-party Third party may refer to: Business * Third-party source, a supplier company not owned by the buyer or seller * Third-party beneficiary, a person who could sue on a contract, despite not being an active party * Third-party insurance, such as a veh ...

, developed elsewhere and assembled into the software system.

Component-based software engineering

For large-scale systems,

component-based development Component-based software engineering (CBSE), also called component-based development (CBD), is a style of software engineering that aims to construct a software system from software component, components that are loosely-Coupling (computer program ...

encourages a disciplined process to manage

complexity Complexity characterizes the behavior of a system or model whose components interact in multiple ways and follow local rules, leading to non-linearity, randomness, collective dynamics, hierarchy, and emergence. The term is generally used to c ...

Framework

Some components conform to a framework technology that allows them to be consumed in a well-known way. Examples include:

CORBA The Common Object Request Broker Architecture (CORBA) is a standard defined by the Object Management Group (OMG) designed to facilitate the communication of systems that are deployed on diverse platforms. CORBA enables collaboration between sy ...

COM Com or COM may refer to: Computing * COM (hardware interface), a serial port interface on IBM PC-compatible computers * COM file, or .com file, short for "command", a file extension for an executable file in MS-DOS * .com, an Internet top-level ...

Enterprise JavaBeans Jakarta Enterprise Beans (EJB; formerly Enterprise JavaBeans) is one of several Java APIs for modular construction of enterprise software. EJB is a server-side software component that encapsulates business logic of an application. An EJB web ...

, and the .NET Framework.

Modeling

Component-based-Software-Engineering-example2

Component design is often modeled visually. In

Unified Modeling Language The Unified Modeling Language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system. UML provides a standard notation for many types of diagrams which can be roughly ...

(UML) 2.0 a component is shown as a rectangle, and an interface is shown as a lollipop to indicate a provided interface and as a socket to indicate consumption of an interface.

History

The idea of reusable software components was promoted by

Douglas McIlroy Malcolm Douglas McIlroy (born 1932) is an American mathematician, engineer, and programmer. As of 2019 he is an Adjunct Professor of Computer Science at Dartmouth College. McIlroy is best known for having originally proposed Unix pipelines and de ...

in his presentation at the NATO Software Engineering Conference of 1968. (One goal of that conference was to resolve the so-called

software crisis Software crisis is a term used in the early days of computing science for the difficulty of writing useful and efficient computer programs in the required time. The software crisis was due to the rapid increases in computer power and the complex ...

of the time.) In the 1970s, McIlroy put this idea into practice with the addition of the

pipeline A pipeline is a system of Pipe (fluid conveyance), pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than of pipeline in 120 countries ...

feature to the

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

Brad Cox Brad J. Cox (May 2, 1944 – January 2, 2021) was an American computer scientist who was known mostly for creating the Objective-C programming language with his business partner Tom Love and for his work in software engineering (specifically so ...

refined the concept of a software component in the 1980s. He attempted to create an infrastructure and market for reusable third-party components by inventing the

Objective-C Objective-C is a high-level general-purpose, object-oriented programming language that adds Smalltalk-style message passing (messaging) to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was ...

programming language.

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

introduced

System Object Model The System Object Model (SOM) is an object-oriented shared library technology developed by IBM that supports defining an interface to an object so that its interface is separate from its implementation. DSOM, a distributed variant based on ...

(SOM) in the early 1990s.

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

introduced

Component Object Model Component Object Model (COM) is a binary-interface technology for software components from Microsoft that enables using objects in a language-neutral way between different programming languages, programming contexts, processes and machines ...

(COM) in the early 1990s. Microsoft built many domain-specific component technologies on COM, including

Distributed Component Object Model Distributed Component Object Model (DCOM) is a proprietary Microsoft technology for communication between software components on networked computers. DCOM, which originally was called "Network OLE", extends Microsoft's COM, and provides the co ...

(DCOM),

Object Linking and Embedding Object Linking and Embedding (OLE) is a proprietary technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control Extension (OCX), a way to develop and use custom user ...

(OLE), and ActiveX.

References

{{Reflist Software architecture Software development Software engineering