Wolfram|Alpha now has a Webservice API which can be used by web applications, desktop or mobile, to query the Wolfram|Alpha engine.
The responses are computed by Wolfram|Alpha in real-time using a supercomputer-class cloud infrastructure. The cloud needs fast processors and relatively little storage contrary to search engines which need lots of storage but slower processors. Search engines look through existing web pages or documents while Wolfram|Alpha computes query results based on raw data.
The queries sent to the API need to have the following REST-style format:
http://api.wolframalpha.com/v1/query?input=pi&appid=XXXX
The application sending this request must provide an APPID obtained from Wolfram Research upon registration. Each application must have its own APIID. The response returned by the Wolfram|Alpha engine is wrapped in XML or it can be returned as HTML/JavaScript. The contract does not allow caching because many of the responses depend on the location of the user making the request considering parameters like geographical position, currency, units, linguistic, and Wolfram|Alpha is in a continuous process of updating the raw data. The requests can specify geo-location information like latitude, longitude, geoIP.
The API is accompanied by several language bindings helping developers to start integrating such API calls in their programs. The languages covered are: .NET (VB), Perl, PHP, Python, Ruby, and soon to come C++, Java and Mathematica.
The API Reference document offers detailed information on how to make API requests and how to interpret the response. A pricing plan applies based on the number of requests sent per month. Grants are offered to selected start-ups and developers writing innovative applications using the API.