Some embodiments of the invention include tools for extracting data of interest from the world wide web (WWW). The extraction is accomplished using descriptions of data of interest. The descriptions of data of interest can include computer programs comprising a sequence of instructions and extractor patterns. The extractor patterns can be developed interactively using a web browser integrated into the graphical development environment for creating the descriptions of data of interest. The instructions can be selected from a predetermined list of instructions designed for extracting information from the WWW. The descriptions of data of interest can be grouped into categories sharing common query elements. Multiple descriptions of data of interest in the same category can executed simultaneously using the same query. The descriptions of data of interest can be accessed by a client computer using a web browser to initiate a query. In some embodiments, the descriptions of data of interest are used to provide information about products available for sale over the WWW.