Extensibility
Encyclopedia
In software engineering
, extensibility (sometimes confused with forward compatibility
) is a system design principle where the implementation takes into consideration future growth. It is a systemic measure of the ability to extend a system
and the level of effort required to implement the extension. Extensions can be through the addition of new functionality or through modification of existing functionality. The central theme is to provide for change - typically enhancements - while minimizing impact to existing system functions.
Although forward compatibility and extensibility are similar, they are not the same. A forward compatible system can accept data from a future version of itself and pick out the "known" part of the data. An example is a text-only word processor ignoring picture data from a future version. An extensible system is one that can be upgraded to fully handle the new data in the newer input format. An example is the above mentioned word processor that can be upgraded to handle picture data or a browser that needs added functionality to successfully load and display certain document or file formats.
In systems architecture
, extensibility means the system is designed to include hooks and mechanisms for expanding/enhancing the system with new capabilities without having to make major changes to the system infrastructure. A good architecture provides the design principles to ensure this—a roadmap for that portion of the road yet to be built. Note that this usually means that capabilities and mechanisms must be built into the final delivery which will not be used in that delivery and, indeed, may never be used. These excess capabilities are not frills, but are necessary for maintainability
and for avoiding early obsolescence
.
Extensibility can also mean that a software system's behavior is modifiable at runtime, without recompiling or changing the original source code. For example, a software system may have a public Application Programming Interface
that allows its behavior to be extended or modified by people who don't have access to the original source code. The extra functionality can be provided through either internally or externally coded extensions.
Although usually applied to engineered systems involving software, it can be applied to any type of engineering. For example, houses can be built with future extensions in mind. The Prince Edward Viaduct
located in Toronto
, Ontario
, Canada
was built to accommodate a future subway line.
Though the application to software is relatively new, the word has been a rare but valid part of English for a long time. The Oxford English Dictionary
cites examples going back to the 17th century.
Software engineering
Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...
, extensibility (sometimes confused with forward compatibility
Forward compatibility
Forward compatibility or upward compatibility is a compatibility concept for systems design, as e.g. backward compatibility. Forward compatibility aims at the ability of a design to gracefully accept input intended for later versions of itself...
) is a system design principle where the implementation takes into consideration future growth. It is a systemic measure of the ability to extend a system
System
System is a set of interacting or interdependent components forming an integrated whole....
and the level of effort required to implement the extension. Extensions can be through the addition of new functionality or through modification of existing functionality. The central theme is to provide for change - typically enhancements - while minimizing impact to existing system functions.
Although forward compatibility and extensibility are similar, they are not the same. A forward compatible system can accept data from a future version of itself and pick out the "known" part of the data. An example is a text-only word processor ignoring picture data from a future version. An extensible system is one that can be upgraded to fully handle the new data in the newer input format. An example is the above mentioned word processor that can be upgraded to handle picture data or a browser that needs added functionality to successfully load and display certain document or file formats.
In systems architecture
Systems architecture
A system architecture or systems architecture is the conceptual model that defines the structure, behavior, and more views of a system.An architecture description is a formal description and representation of a system, organized in a way that supports reasoning about the structure of the system...
, extensibility means the system is designed to include hooks and mechanisms for expanding/enhancing the system with new capabilities without having to make major changes to the system infrastructure. A good architecture provides the design principles to ensure this—a roadmap for that portion of the road yet to be built. Note that this usually means that capabilities and mechanisms must be built into the final delivery which will not be used in that delivery and, indeed, may never be used. These excess capabilities are not frills, but are necessary for 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...
and for avoiding early obsolescence
Obsolescence
Obsolescence is the state of being which occurs when an object, service or practice is no longer wanted even though it may still be in good working order. Obsolescence frequently occurs because a replacement has become available that is superior in one or more aspects. Obsolete refers to something...
.
Extensibility can also mean that a software system's behavior is modifiable at runtime, without recompiling or changing the original source code. For example, a software system may have a public Application Programming Interface
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
that allows its behavior to be extended or modified by people who don't have access to the original source code. The extra functionality can be provided through either internally or externally coded extensions.
Although usually applied to engineered systems involving software, it can be applied to any type of engineering. For example, houses can be built with future extensions in mind. The Prince Edward Viaduct
Prince Edward Viaduct
The Prince Edward Viaduct System, commonly referred to as the Bloor Viaduct or the viaduct, is the name of a truss arch bridge system in Toronto, Ontario, Canada that connects Bloor Street East, on the west side of the system, with Danforth Avenue on the east...
located in Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...
, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
was built to accommodate a future subway line.
Though the application to software is relatively new, the word has been a rare but valid part of English for a long time. The Oxford English Dictionary
Oxford English Dictionary
The Oxford English Dictionary , published by the Oxford University Press, is the self-styled premier dictionary of the English language. Two fully bound print editions of the OED have been published under its current name, in 1928 and 1989. The first edition was published in twelve volumes , and...
cites examples going back to the 17th century.