Improved techniques for processing queries in full-text systems

In static full-text retrieval systems, which accommodate metrical as well as Boolean operators, the traditional approach to query processing uses a "concordance", from which large sets of coordinates are retrieved and then merged and/or collated. Alternatively, in a system with £ documents, the concordance can be replaced by a set of bit-maps of fixed length £, which are constructed for every different word of the database and serve as occurrence maps. We propose to combine the concordance and bit-map approaches, and show how this can speed up the processing of queries: fast ANDing and ORing of the maps in a preprocessing stage, lead to large I/O savings in collating coordinates of keywords needed to satisfy the metrical and Boolean constraints. Moreover, the bit-maps give partial information on the distribution of the coordinates of the keywords, which can be used when queries must be processed by stages, due to their complexity and the sizes of the involved sets of coordinates. The new techniques are partially implemented at the Responsa Retrieval Project.