Abstract:

For querying a universal relations system the user only has to specify the output attributes he is interested in and the conditions for these attributes; the universal relation system computes the relevant part of the database scheme with respect to the query, the query hypergraph, and subsequently relations and join conditions corresponding to the query hypergraph. We introduce a universal relation forntend working with an SQL-like-language. In particular, we allow universal relation queries with SQL-features like aggregate functions, the GROUP BY and ORDER BY clause. We concentrate on the class of gamma-acyclic database schemes, where the universal relation queries are sematically unambiguous.