Conjunctive Query Equivalence of Keyed Relational Schemas
Authors: 
Joseph Albert
Authors: 
Yannis Ioannidis
Authors: 
Raghu Ramakrishnan
Date published: 
1997
Published In: 
16th Int’l ACM PODS Symposium, Tucson, AZ, May 1997
Type: 
Conference Article
Abstract: 

The notion of when two schemas are equivalent is fundamental to database design, schema integration, and data model translation. An important notion of schema equivalence, query equivalence was introduced in [3], and used to evaluate the correctness of schema transformations. The logically equivalent notion of calculous equivalence, as well as three progressively weaker notions of schema equivalence were introduced in 1984 by Hull [9, 10], who showed that two schemas with no dependencies are equivalent (under all four notions of equivalence) if and only if they are identical (up to renaming and re-ordering of attributes and relations). Hull also conjectured that the same result holds for schemas with primary keys. In this work, we resolve the conjecture in the affirmative for the case of query equivalence based on mappings using conjunctive relational queries with equality selections.

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