Indexing Structures Derived from Syntax in TREC-3: System Description

This paper describes an approach to information retrieval based on a syntactic analysis of the document texts and user queries, and from that analysis, the construction of tree structures (TSAs) to encode and capture language ambiguities. TSAs are constructed at the clause level and thus each document can yield many TSAs and each query may be represented by several TSAs. The TSAs from documents and from queries are then matched and their degrees of overlap between individual TSAs are computed and then aggregated to yield a score for each document, which is then used in ranking the collection. This paper presents the system description when benchmarking our retrieval strategy on category B of TREC-3, i.e. on c.550 Mbytes of the Wall Street Journal newspaper texts. The implementation is based on a two-stage retrieval where a statisticallybased pre-fetch retrieval retrieves the set of WSJ articles for the more computationally expensive language based processing. The results of our retrieval system in terms of precision and recall are disappointing and an analysis of why is also included. Part of this analysis includes a direct comparison between our system and some mainstream IR approaches. In addition to performing ad hoc retrieval on texts in English, we have also performed ad hoc retrieval on texts in Spanish using a weighted trigram approach, and this is outlined and performance results given in an appendix.