Free text information retrieval has traditionally concentrated on textual databases of titles and abstracts, with the addition of indexing on keywords sometimes chosen from an approved thesaurus. The first problem from the user's point of view is the choice of the appropriate keyword descriptor and the existence of many synonyms for some concepts. The second problem, which arose in the context of the HELP system, is that system designers tend to assume the user has an underlying knowledge base of concepts implying that certain terms did not require any explanation. This can lead to much frustration. The third problem is that language changes
with respect to time, so material which was indexed under, 'Man-Machine Interface (MMI)' ten years ago, might well be missed in a search using 'Human-Computer Interaction (HCI)'. Users therefore need to have a sense of the development of the language of the topic.