Wolfram Alpha Java Library by Todd Gayley can access the API to add reference features based on a computational knowledge engine. Unlike search services that only provide a list of web pages where users can find answers based on queries, this reference offers responses from external curated data. Such mechanism can be useful to integrate with the API considering the development of desktop and mobile applications using Java language.
Folks interested in "open knowledge" should check out CKAN (Comprehensive Knowledge Archive Network)
CKAN is the Comprehensive Knowledge Archive Network, a registry of open knowledge packages and projects (and a few closed ones).
Organizations are continuously engaged in mining the large amounts of information that is generated daily on social networks. As is natural, they would like to understand trends and any mentions in real time. Topsy, a realtime search engine has been indexing Twitter data on a daily basis and providing the Topsy API, to sift through that information. It has now added another feather in its cap by adding public Google Plus posts to its index.