Automated generation of category-specific thesauri for interactive query expansion

The categorisation of documents into subject-specific categories is a useful enhancement for large document collections addressed by information retrieval systems, as a user can first browse a category tree in search of the category that best matches her interests, and then issue a query for more specific documents "from within the category". This approach combines two modalities in information seeking that are most popular in Web-based search engines, i.e. category-based site browsing (as exemplified by e.g. YAHOO) and keyword-based document querying (as exemplified by e.g. ALTAVISTA). Appropriate query expansion tools need to be provided, though, in order to allow the user to incrementally refine her query through further retrieval passes, thus allowing the system to produce a series of subsequent document rankings that hopefully converge to the user's expected ranking. In this work we propose that automatically generated, category-specific "associative" thesauri be used for such purpose. We discuss a method for their generation, and discuss how the thesaurus specific to a given category may usefully be endowed with "gateways" to the thesauri specific to its parent and children categories.