The application program interface (API) is a set of building blocks for programmers.
APIs are made up of routines, protocols, and tools. Most operating environments provide an API so that programmers can write applications consistent with that environment. For example, developing software using the Windows API ensures that your user interface will be consistent with other Windows applications, making it easier for users to learn your new programs.
Use on the Web
Web APIs provide simple ways to interact with websites. Using an API, you can extract public data from sites like del.icio.us, Flickr and Digg to create mashups, reuse data or just about anything else you can imagine.
APIs are also useful for extracting your own private data from a web service so that you can back it up elsewhere or display it on another site.
When talking about APIs you’ll here the following terms quite a bit.
Common Web API Related Terms
- Web service/API — These terms are largely interchangeable and simple refer to the ways you can interact with the data on your favorite websites.
- Method — A method is just one aspect of an API; you might also see methods refered to a functions. For instance, if you’re interacting with Flickr, you might want to get your public photos. To do so you would use the get_user_photos method.
- Response — The information returned by the API method that you’ve called.
- REST — Short for Representational State Transfer. REST treats data as a web document that lives at a specific URL. REST APIs use standard HTTP requests such as GET, PUT, HEAD, DELETE and POST to interact with data.
- XML-RPC — This older API scheme formats method calls and responses as XML documents which are sent over HTTP.
- SOAP — Simple Object Access Protocol. A W3C standard for passing messages across the network. SOAP is the successor to XML-RPC. It’s complexity has led many to disparage SOAP and with more APIs leaning toward REST, SOAP’s future is uncertain.