Property:Subcategory of
[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 ]
"Subcategory of" is a predefined property to define that a category is a subcategory of another and is provided by Semantic MediaWiki. 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.