components. A good API makes it easier to develop a computer program by providing all the building blocks, which are then put together by the programmer. An API may be for a web-based system, operating system, database system, computer hardware, or software library. An API specification can take many forms, but often includes specifications for routines, data structures, object classes, variables, or remote calls. POSIX, Windows API and ASPI are examples of different forms of APIs. Documentation for the API usually is provided to facilitate usage and implementation. Contents 1 Purpose 2 History 3 Uses 3.1 Libraries and frameworks 3.2 Operating systems 3.3 Remote APIs 3.4 Web APIs 4 Design 5 Release policies 5.1 Public API implications 6 Documentation 7 Copyright controversy 8 Examples 9 See also 10 References 11 Further reading Purpose In building applications, an API simplifies programming by abstracting the underlying implementation and only exposing objects or actions the developer needs. While a graphical interface for an email client might provide a user with a button that performs all the steps for fetching and highlighting new emails, an API for file input/output might give the developer a function that copies a file from one location to another without requiring that the developer understand the file system operations occurring behind the scenes.[1] History The term API seems to appear for the first time in the article of Ira W. Cotton, Data structures and techniques for remote computer graphics, published in 1968. Uses Libraries and frameworks An API usually is related to a software library. The API describes and prescribes the "expected behavior" (a specification) while the library is an "actual implementation" of this set of rules. A single API can have multiple implementations (or none, being abstract) in the form of different libraries that share the same programming interface. The separation of the API from its implementation can allow programs written in one language to use a library written in another. For example, because Scala and Java compile to compatible bytecode, Scala developers can take advantage of any Java API.[2]