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Enhancing the expressive power of the U-Datalog language

Published online by Cambridge University Press:  03 April 2001

University of Milan, Via Comelico 39, 20135 Milano, Italy; e-mail:
University of Genova, Via Dodecaneso 35, 16146 Genova, Italy; e-mail:
University of Pisa, Corso Italia, 40, 56125 Pisa, Italy; e-mail:


U-Datalog has been developed with the aim of providing a set-oriented logical update language, guaranteeing update parallelism in the context of a Datalog-like language. In U-Datalog, updates are expressed by introducing constraints (+p(X), to denote insertion, and −p(X), to denote deletion) inside Datalog rules. A U-Datalog program can be interpreted as a CLP program. In this framework, a set of updates (constraints) is satisfiable if it does not represent an inconsistent theory, that is, it does not require the insertion and the deletion of the same fact. This approach resembles a very simple form of negation. However, on the other hand, U-Datalog does not provide any mechanism to explicitly deal with negative information, resulting in a language with limited expressive power. In this paper, we provide a semantics, based on stratification, handling the use of negated atoms in U-Datalog programs, and we show which problems arise in defining a compositional semantics.

Technical note
© 2001 Cambridge University Press

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