Recent trends in automatic information retrieval

Substantial successes were achieved in the early years in automatic indexing and retrieval using single term indexing theories with term weight assignments based on frequency considerations. The development of more refined indexing systems using thesaurus aids and automatically constructed term association maps changed the retrieval effectiveness only slightly. The recent introduction of the relevance concept in the form of probabilistic retrieval models provided a firm basis for term weighting and document ranking practices. However, the probabilistic methods were not helpful in substantially enhancing the retrieval effectiveness.