Property:Query source
[http://www.nga.gov/content/ngaweb/research/casva/research-projects.html A Project of the National Gallery of Art, Center for Advanced Study in the Visual Arts ]
"Query source" is a predefined property provided by Semantic MediaWiki that identifies alternative (e.g. remote, federated) query sources. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.