• Users have no detailed knowledge of – The collection makeup – The retrieval environment • Scenario of (Web) IR

1. An initial (naive) query posed to retrieve relevant docs 2. Docs retrieved are examined for relevance and a new improved query formulation is constructed and posed again Difficult to formulate queries Expand the original query with new terms (query expansion) and rewight the terms in the expanded query (term weighting) 3Query Reformulation • Approaches through query expansion (QE) and terming weighting – Feedback information from the user • Relevance feedback –With vector, probabilistic models et al. – Information derived from the set of documents initially retrieved (called local set of documents) • Local analysis – Local clustering, local context analysis – Global information derived from document collection • Global analysis – Similar thesaurus or statistical thesauru