Representing Roles in Universal Scheme Interfaces.

Users of a relational database must explicitly navigate between relations in order to establish a connection among a set of attributes spanning several relation schemes. While a universal scheme interface to a relational database provides users with automatic navigation, it usually imposes on the database a unique role assumption. This assumption requires every attribute name to represent a unique role in the database, so that connections among sets of attributes are unambiguous. A drawback to this requirement is that several attributes can represent the same underlying class of entities, but the relationship among these attributes is not captured in the database scheme. As the standard method for relating attributes uses natural joins, some semantically meaningful connections among attributes are lost. We take a step toward removing this drawback by explicitly storing role relationships between attributes. The connections lost due to the enforcement of the unique role assumption are recovered via equijoins based on these role relationships. We give conditions on such role connections to ensure that they are semantically consistent with other connections, and show how to extend PIQUE, an existing universal scheme interface, to use this role information. [ABSTRACT FROM AUTHOR]