As far as web search tools go, few have generated as much hype as Wolfram Alpha. The service, which bills itself as a "computational knowledge engine," differs from search engines such as Google, in that it does not return lists of web pages. Rather, Wolfram Alpha attempts to calculate answers to user queries. For example, a query of "los angeles county median household income" will return the result "$43,518."
Access to Wolfram Alpha's computational search results are provided via a RESTful "Query" API, which allows developers to submit query strings, much like users do at the Wolfram Alpha website. Because Alpha has limited language processing capabilities, it cannot parse every query string it receives, so developers can choose to first have their query strings checked to see if Alpha can handle the format of the question. The Query API has many features, such as the ability to request location specific information, or the ability to set the default return currency for economic queries. More details at our Wolfram Alpha API profile.
CNET's Stephen Shankland describes the potential power of Alpha's API:
There's an API for Alpha that could help the service catch on. It's a mashup expert's dream, and the fact that Wolfram licenses data not publicly available, then vets it to boot, means a lot of people will be willing to incorporate it on their Web sites.
Wolfram Alpha's Query API also provides very powerful return formats: Queries can be returned in text formats such as MathML, Mathematica, plain text and more. Alpha can also return queries as images in Gif, PDF, or HTML formats. In order to use the Wolfram Alpha Query API, developers are required to obtain a development key (see this page).
In the future, Wolfram Alpha plans to release a more detailed API (called the "Data" API) which will allow developers to have more control over the data sets used in the query result. Wolfram Alpha's API documentation describes the upcoming Data API:
Wolfram|Alpha has a simple yet expressive internal mechanism for extracting specific pieces of data from its enormous store of curated data. In the near future we will be exposing this facility via a web API. This type of request can be used when you want a single result value or set of values and can describe the data you want in a precise way (or at least ask Wolfram|Alpha to assist you in determining the correct way to ask).
Wolfram Alpha claims to have a "trillions" of pieces of data in its database, which might make it the most comprehensive semantic search engine available. However, Alpha is not the only semantic search that offers an API. True Knowledge, another natural language query engine which we've recently covered, differs from Wolfram Alpha in that it focuses on returning user queries in a human readable style. While True Knowledge's servers might not have access to the huge amount of data that Alpha does, developers may appreciate the user-friendly query results.