Optimised phrase querying and browsing of large text databases

Most search systems for querying large document collections-for example, web search engines-are based on well-understood information retrieval principles. These systems are both efficient and effective in finding answers to many user information needs, expressed through informal ranked or structured Boolean queries. Phrase querying and browsing are additional techniques that can augment or replace conventional querying tools. In this paper we propose optimisations for phrase querying with a nextword index, an efficient structure for phrase-based searching. We show that careful consideration of which search terms are evaluated in a query plan and optimisation of the order of evaluation of the plan can reduce query evaluation costs by more than a factor of five. We conclude that, for phrase querying and browsing with nextword indexes, an ordered query plan should be used for all browsing and querying. Moreover, we show that optimised phrase querying is practical on large text collections.