Query expansion (or) is the process of supplement ing or replacing the original query terms with additional terms either at the search formulation or search reformulation stages This can he done automatically by the system or semi-automatically with asststance from the user. Different approaches to implementing or are considered in three on line catalogues. An evaluative study of an automatic on facil ity in ONNPI. an experimental system developed at City Uni versity, revealed that expanded searches were useful to a substantial proportion of users.
Query expansion methods have been studied for a long time - with debatable success in many instances. In this paper we present a probabilistic query expansion model based on a similarity thesaurus which was constructed automatically. A similarity thesaurus reflects domain knowledge about the particular collection from which it is constructed. We address the two important issues with query expansion: the selection and the weighting of additional search terms. In contrast to earlier methods, our queries are expanded by adding those terms that are most similar to the concept of the query, rather than selecting terms that are similar to the query terms. Our experiments show that this kind of query expansion results in a notable improvement in the retrieval effectiveness when measured using both recall-precision and usefulness.
We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.