The Google data APIs ("GData" for short) provide a simple standard protocol for reading and writing data on the web. GData combines common XML-based syndication formats (Atom and RSS) with a feed-publishing system based on the Atom publishing protocol, plus some extensions for handling queries. GData is a new protocol based on Atom 1.0 and RSS 2.0. To acquire information from a service that supports GData, you send an HTTP GET request; the service returns results as an Atom or RSS feed. You can update data (where supported by a particular GData service) by sending an HTTP PUT request, an approach based on the Atom Publishing Protocol. All sorts of services can provide GData feeds, from public services like blog feeds or news syndication feeds to personalized data like email or calendar events or task-list items. The RSS and Atom models are extensible, so each feed provider can define its own extensions and semantics as desired. A feed provider can provide read-only feeds (such as a search-results feed) or read/write feeds (such as a calendar application). For example, a blogging application might provide a feed for each blog, and a comment feed for each blog entry. A calendar application might allow you to send full-text search queries using the GData protocol, and return results in the GData syndication format. Because GData is built on basic technologies—HTTP and common syndication models—you can send GData requests and process the resulting feeds in a variety of ways: traditional syndication aggregators/feed readers, JavaScript/AJAX-based clients in a web browser, standalone applications, or any other approach you like. The GData protocol is language-neutral; you can write a client in any programming language that lets you issue HTTP requests and parse XML-based responses. Creating and deleting a feed is left up to the service; the GData protocol does not provide ways to create or delete a feed.
