Role-based query processing in multidatabase systems

We address the problem of data integration and query processing in multidatabase systems in the presence of conflicting values for the attributes that correspond to different instances of the same real-world object appearing in multiple roles. We present a new method for schema and data integration in multidatabase systems that presents the answer to the query as a set of sets representing the distinct intersections between the relations representing the various roles of interest. We present extensions to MSQL that allow us to express role-sets and quantifiers applied to them. We further develop a strategy for query processing based on our role-based model. Our method allows for local selection for all queries with/without aggregation and thus reduces the amount of data transmitted. In addition, it makes efficient use of merge-sort techniques to generate the role-sets and compute joins at the global query site.