application program interface (API)

A rigorous definition of the method by which a program can access the services provided by another program. Developers of an API often provide libraries of callable functions that implement the API. Examples include: the 4GL API enables a C program to call a 4GL routine; Motif enables a C program to call X Windows; INFORMIX-ESQL, which is an SQL API, enables a C program to access a database. There can be many different APIs that provide access to the same set of services, though possibly at different points of entry. In some cases, the same API can be used to access different services. (Example: NetBIOS is a network API that is protocol-independent and often used to access a variety of different protocols such as OSI, TCP/IP, and so on.)

See also application development tool.