Abstract
It has been observed that, for some database schemes, users may have difficulties retrieving correct information, even for simple queries. The problem occurs when some implicit “piece” of information, defined on some subset of a relation scheme, is not explicitly represented in the database state. In this situation, users may be required to know how the state and the constraints interact before they can retrieve the information correctly.In this paper, the formal notion ofembedded-completenessis proposed, and it is shown that schemes with this property avoid the problem described above. A polynomial-time algorithm is given to test whether a database scheme is independent and embedded-complete. Under the assumption of independence, it is shown that embedded-complete schemes allow efficient computation of optimal relational algebra expressions equivalent to theX-total projection, for any set of attributesX.
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