Roles and their role in posing recursive queries

摘要

We show how to use the entity-relationship diagram as a vehicle for specifying the semantics of attributes. A main contribution of this work is a strategy for creating entity-relationship diagrams that make explicit the role of attributes that are over the same domain. Recursive queries can be posed over the universal relation when attributes are over the same domain and play distinct roles. We show how to extend a query language, that poses queries over the universal relation, to include the ability to express recursive queries.