1. A method for providing information from a corpus of content items to a client, the method comprising: defining a plurality of grouping labels; automatically building an index configured to identify, for each of the plurality of grouping labels, each of the content items in the corpus that includes that grouping label; receiving from a client a request for identification of content items related to a first content item, the request including a first one of the plurality of grouping labels contained within the first content item; accessing the index to identify a second content item having the first one of the plurality of grouping labels included therein; and returning a reference to the second content item to the client.