Maintainability
- isolate defects or their cause,
- correct defects or their cause,
- repair or replace faulty or worn-out components without having to replace still working parts,
- prevent unexpected breakdowns,
- maximize a product's useful life,
- maximize efficiency, reliability, and safety,
- meet new requirements,
- make future maintenance easier, or
- cope with a changed environment.
In some cases, maintainability involves a system of continuous improvement - learning from the past in order to improve the ability to maintain systems, or improve reliability of systems based on maintenance experience.
In telecommunication and several other engineering fields, the term maintainability has the following meanings:
- A characteristic of design and installation, expressed as the probability that an item will be retained in or restored to a specified condition within a given period of time, when the maintenance is performed in accordance with prescribed procedures and resources.
- The ease with which maintenance of a functional unit can be performed in accordance with prescribed requirements.
Extensibility
In software engineering, extensibility (not to be confused with forward compatibility) is a system design principle where the implementation takes future growth into consideration. 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.
Extensibility is a software design principle defined as a system’s ability to have new functionality extended, in which the system’s internal structure and data flow are minimally or not affected, particularly that recompiling or changing the original source code is unnecessary when changing a system’s behavior, either by the creator or other programmers.[1] Because software systems are long lived and will be modified for new features and added functionalities demanded by users, extensibility enables developers to expand or add to the software’s capabilities and facilitates systematic reuse. Some of its approaches include facilities for allowing users’ own program routines to be inserted and the abilities to define new data types as well as to define new formatting markup tags.[2]
