application program interface

An application programming interface (API) is a source code interface that an operating system or library provides to support requests for services to be made of it by computer programs.^[1]

API versus ABI

An API is similar to an application binary interface (ABI) in that both specify details of how two independent computer programs can interact. However, an API is typically defined at a higher level (i.e., in terms of a programming language that can be compiled when an application is built, rather than an explicit low level description of how data is laid out in memory). For example, the Linux Standard Base is an ABI, while POSIX is an API.^[2]

Distinction between API specification and its implementation

The software that provides the functionality described by an API is said to be an implementation of the API. The API itself is abstract, in that it specifies an interface and the behavior of the identifiers specified in that interface, it does not specify how the behavior might be implemented.

Release policies

There are two general kinds of API publishing policies that are often encountered:

1. Some companies protect information on their APIs from the general public. For example, Sony used to make its official PlayStation 2 API available only to licensed PlayStation developers. This enabled Sony to control who wrote PlayStation 2 games. Such control can have quality control benefits and potential license revenue.
2. Some companies make their APIs freely available. For example, until the release of Windows Vista, Microsoft made most of its API information public, so that software would be written for the Windows platform.

It is to be expected that companies base their choice of publishing policy on maximizing benefit to themselves.

Some example APIs

• The PC BIOS call interface
• Single UNIX Specification (SUS)
• Windows API
• Java Platform, Standard Edition API
• Java Platform, Enterprise Edition APIs
• ASPI for SCSI device interfacing
• Carbon and Cocoa for the Macintosh OS
• OpenGL cross-platform 3D graphics API
• DirectX for Microsoft Windows
• Simple DirectMedia Layer (SDL)
• Google Maps API
• YouTube API
• Digg API
• MediaWiki API

See also

• Application binary interface (ABI)
• Document Object Model
• Open Service Interface Definitions (OSID)
• Plugin
• software development kit (SDK)
• Mashup (web application hybrid)
• Web service

References

1. ^ QuickStudy: Application Programming Interface (API). ComputerWorld.
2. ^ Update on Standards. USENIX.

External links

• How to design a good API and why it matters-PDF
• The trends and the role of API-driven mashup building tools in the enterprise computing
• Service-Oriented Architecture (SOA): The Road to Enterprise Application Integration (EAI)
• Organized list of API references with fast as-you-type search

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