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The Impact of Active Domain Predicates on Guarded Existential Rules

Gottlob G., Pieris A., Šimkus M.

Fundamenta Informaticae

2018

Vol. 159, nr 1/2

123--146

It is realistic to assume that a database management system provides access to the active domain via built-in relations. Therefore, databases that include designated predicates that hold the active domain, which we call product databases, form a natural notion that deserves our attention. An important issue then is to look at the consequences of product databases for the expressiveness and complexity of central existential rule languages. We focus on guarded-based existential rules, and we investigate the impact of product databases on their expressive power and complexity. We show that the queries expressed via (frontier-)guarded rules gain in expressiveness, and in fact, they have the same expressive power as Datalog. On the other hand, there is no impact on the expressiveness of the queries specified via weakly-(frontier-)guarded rules since they are powerful enough to explicitly compute the predicates needed to access the active domain. We also observe that there is no impact on the complexity of the query languages in question.

Constraint-Based Approach to Semistructured Data

Hacid M-S., Toumani F., Elmagarmid A.K.

Fundamenta Informaticae

2001

Vol. 47, nr 1,2

53-73

In this paper we consider how constraint-based technology can be used to query semistructured data. As many concerns in semistructured data (e.g., representing and retrieving) are also found in computational linguistics, this last area could provide an interesting angle to attack some of the problems regarding semistructured data. We present a formalism based on feature logics1 for querying semistructured data. The formalism is a hybrid one in the sense that it combines clauses with path constraints. The resulting language has a clear declarative and operational semantics based on the notion of extended active domain.