A data structure, apparatuses and methods for expanding a search query to be used by a web search engine is provided. The search query is expanded by accessing a concept knowledge base data structure having concept data objects and term data objects with each term data object defining a term and associated with at least one of the concept data objects. Search terms making up the search query are matched to term data objects and a concept set is generated containing concept data objects associated with the term data objects. A second set of term data objects are generated by using the concept data objects to locate term data objects associated with the concept data objects. A user can then select one of the term data objects in the second set to expand the user's search query.