INFORMATION-RETRIEVAL AS COUNTERFACTUAL

Relevance, one of the fundamental notions in information retrieval (IR ), has long been studied from a cognitive point of view. It is known t hat relevance depends not only on the topic of the document and the in formation need expressed in a query, but also on other 'situational' f actors in the retrieval situation, such as the user's previous knowled ge, background, intentions and so on. Formal models, on the other hand , usually consider relevance from a system point of view, i.e. they is olate relevance in a restricted context in which only the topic matter s. One of the reasons for this very partial modeling is due to the ina ppropriateness of standard formal tools for describing relevance in a general context. This paper is an attempt to identify a more appropria te logical framework for the modeling. Counterfactual conditional logi c is examined with respect to the IR requirements, indicating the logi c's high potential value for this task. A particular conditional logic is then defined which, in comparison with previous developments on co nditional logic, is better suited to IR. The new model gives an insigh t into the phenomena related to the 'situational' factors of relevance judgment which, until now, have not been considered.