An asynchronus server query (ASQ) is a form of web communication between a client and server that involves dynamically updating part of a webpage without having to reload it all. ASQs are typically achieved using javascript and/or iframes with the aim of giving web applications similar responsiveness to desktop applications (see Rich Internet application).

In the past, if a user wanted to send information to a server then they would have to issue a 'GET' or 'POST' request via their browser for a complete page. A problem with this method arises in cases where only a small amount of information is involved, or only a part of a page needs to be updated. For example, if a website allows users to read their email, then having to request the whole page just to check if you have any new mail is a significant drain on both the server's resources and the user's time. Using an ASQ allows a simple check to be made to see if the user has any new mail waiting - only if there is will the page be refreshed.

Implementation

Currently, the most common method of achieving such asychronus client/server communication is using the XMLHttpRequest javascript object. Ajax is a term coined for the use of XMLHttpRequest and XML although it has come to refer to any dynamic updating of webpages that requires querying a web server. Although technology to use ASQs has existed for several years, it is likely that it is Google's heavy use of ASQ-style applications and greater consistency in the implementation of relevant technologies that has brought this programming methodology to the mainstream.