| Software development process | |
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| Activities and steps | |
| Requirements · Specification Architecture · Design Implementation · Testing Deployment · Maintenance |
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| Methodologies | |
| Agile · Cleanroom · Iterative RAD · RUP · Spiral Waterfall · XP · Lean Scrum · V-Model · TDD |
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| Supporting disciplines | |
| Configuration management Documentation Quality assurance (SQA) Project management User experience design |
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| Tools | |
| Compiler · Debugger · Profiler GUI designer · IDE |
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The software architecture of a program or computing system is the structure or structures of the system, which comprise software components, the externally visible properties of those components, and the relationships between them. The term also refers to documentation of a system's software architecture. Documenting software architecture facilitates communication between stakeholders, documents early decisions about high-level design, and allows reuse of design components and patterns between projects.[1]
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The field of computer science has come across problems associated with complexity since its formation.[2] Earlier problems of complexity were solved by developers by choosing the right data structures, developing algorithms, and by applying the concept of separation of concerns. Although the term “software architecture” is relatively new to the industry, the fundamental principles of the field have been applied sporadically by software engineering pioneers since the mid 1980s. Early attempts to capture and explain software architecture of a system were imprecise and disorganized, often characterized by a set of box-and-line diagrams.[3] During the 1990s there was a concentrated effort to define and codify fundamental aspects of the discipline. Initial sets of design patterns, styles, best practices, description languages, and formal logic were developed during that time.
The software architecture discipline is centered on the idea of reducing complexity through abstraction and separation of concerns. To date there is still no agreement on the precise definition of the term “software architecture”.[4]
As a maturing discipline with no clear rules on the right way to build a system, designing software architecture is still a mix of art and science. The “art” aspect of software architecture is because a commercial software system supports some aspect of a business or a mission. How a system supports key business drivers is described via scenarios as non-functional requirements of a system, also known as quality attributes, determine how a system will behave.[5] Every system is unique due to the nature of the business drivers it supports, as such the degree of quality attributes exhibited by a system such as fault-tolerance, backward compatibility, extensibility, reliability, maintainability, availability, security, usability, and such other –ilities will vary with each implementation.[5] To bring a software architecture user's perspective into the software architecture, it can be said that software architecture gives the direction to take steps and do the tasks involved in each such user's speciality area and interest e.g. the stakeholders of software systems, the software developer, the software system operational support group, the software maintenance specialists, the deployer, the tester and also the business end user. In this sense software architecture is really the amalgamation of the multiple perspectives a system always embodies. The fact that those several different perspectives can be put together into a software architecture stands as the vindication of the need and justification of creation of software architecture before the software development in a project attains maturity.
The origin of software architecture as a concept was first identified in the research work of Edsger Dijkstra in 1968 and David Parnas in the early 1970s. These scientists emphasized that the structure of a software system matters and getting the structure right is critical. The study of the field increased in popularity since the early 1990s with research work concentrating on architectural styles (patterns), architecture description languages, architecture documentation, and formal methods[6].
Research institutions have played a prominent role in furthering software architecture as a discipline. Mary Shaw and David Garlan of Carnegie Mellon wrote a book titled Software Architecture: Perspectives on an Emerging Discipline in 1996, which brought forward the concepts in Software Architecture, such as components, connectors, styles and so on. The University of California, Irvine's Institute for Software Research's efforts in software architecture research is directed primarily in architectural styles, architecture description languages, and dynamic architectures.
The IEEE 1471: ANSI/IEEE 1471-2000: Recommended Practice for Architecture Description of Software-Intensive Systems is the first formal standard in the area of software architecture, and was adopted in 2007 by ISO as ISO/IEC 42010:2007.
Architecture description languages (ADLs) are used to describe a Software Architecture. Several different ADLs have been developed by different organizations, including AADL (SAE standard), Wright (developed by Carnegie Mellon), Acme (developed by Carnegie Mellon), xADL (developed by UCI), Darwin (developed by Imperial College London), and DAOP-ADL (developed by University of Málaga). Common elements of an ADL are component, connector and configuration.
Software architecture is commonly organized in views[7], which are analogous to the different types of blueprints made in building architecture. Within the ontology established by ANSI/IEEE 1471-2000, views are instances of viewpoints, where a viewpoint exists to describe the architecture in question from the perspective of a given set of stakeholders and their concerns.
Some possible views (actually, viewpoints in the 1471 ontology) are:
Several languages for describing software architectures have been devised, but no consensus has yet been reached on which symbol-set and view-system should be adopted. The UML was established as a standard "to model systems (and not just software)," and thus applies to views about software architecture.
Frameworks related to the domain of software architecture are:
Other architectures such as the Zachman Framework, DODAF, and TOGAF relate to the field of Enterprise architecture.
Software architecture is the realization of non-functional requirements, while software design is the realization of functional requirements.
Software architecture, also described as strategic design, is an activity concerned with global design constraints, such as programming paradigms, architectural styles, component-based software engineering standards, design principles, and law-governed regularities. Detailed design, also described as tactical design, is an activity concerned with local design constraints, such as design patterns, architectural patterns, programming idioms, and refactorings. According to the Intension/Locality Hypothesis[8], the distinction between architectural and detailed design is defined by the Locality Criterion[8], according to which a statement about software design is non-local (architectural) if and only if a program that satisfies it can be expanded into a program which does not. For example, the client–server style is architectural (strategic) because a program that is built on this principle can be expanded into a program which is not client–server; for example, by adding peer-to-peer nodes.
Architecture is design but not all design is architectural. In practice, the architect is the one who draws the line between software architecture (architectural design) and detailed design (non-architectural design). There aren't rules or guidelines that fit all cases.
There are many common ways of designing computer software modules and their communications, among them:
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