Processing Structural Constraints

When searching unstructured plain-text the user is limited in the expressive power of their query – they can only ask for documents that are about something. When structure is present in the document, and with a query language that supports its use, the user is able to write far more precise queries. For example, searching for smith in a document is not necessarily equivalent to searching for smith as an author of a document. This increase in expressive power should lead to an increase in precision with no loss in recall. By specifying that smith should be the author, all those instances where smith was the profession will be dropped (increasing precision), while all those in which smith is the author will still be found (maintaining recall).