Using Quality of Data Metadata for Source Selection and Ranking

The World Wide Web has become the preferred medium for the dissemination of information in virtually every domain of activity. Standards and formats for data interchange have addressed the issue of interoperability among heterogeneous sources. However, access to data is still hindered by the challenge of locating data relevant to a particular problem. Further, after a set of relevant sources have been identied, one must still decide which source is best suited for a given task and appropriately rank these sources. WWW sources typically may cover di erent domains and they may di er considerably with respect to a variety of quality of data (qod) parameters which include completeness, recency of update, granularity, etc. In order to solve this problem of source selection and ranking using qod parameters, we maintain metadata about source content and quality of data or scqd metadata. We use a data model for representing scqd metadata similar to those used in a data warehouse environment. We present a query language for source selection and ranking that supports both strict and fuzzy matching of scqd metadata. We then discuss the e cient organization of the scqd metadata to support source selection. We discuss how scqd metadata can be organized in partially ordered sets (po-sets) to support e cient query processing. Some queries can only be answered by a combination of sources. To avoid enumerating an exponential number of possible combinations, we propose a heuristic that gradually extends the associated po-set towards a lattice. We outline the loss of accuracy of the qod metadata incurred by this approach. [section] [section]