We define XPathLog as a Datalog-style extension of XPath. XPathLog provides a clear, declarative language for querying and manipulating XML whose perspectives are especially in XML data integration. In our characterization, the formal semantics is defined wrt. an edge-labeled graph-based model, which covers the XML data model. We give a complete, logic-based characterization of XML data and the main language concept for XML, XPath. XPath-Logic extends the XPath language with variable bindings and embeds it into first-order logic. XPathLog is then the Horn fragment of XPath-Logic, providing a Datalog-style, rule-based language for querying and manipulating XML data. The model-theoretic semantics of XPath-Logic serves as the base of XPathLog as a logic-programming language, whereas also an equivalent answer-set semantics for evaluating XPathLog queries is given. In contrast to other approaches, the XPath syntax and semantics is also used for a declarative specification how the database should be updated: when used in rule heads, XPath filters are interpreted as specifications of elements and properties which should be added to the database.

Referential actions are specialized triggers for automatically maintaining referential integrity in databases. While the local effects of referential actions can be grasped easily, it is far from obvious what the global semantics of a set of interacting referential actions should be. In particular, when using procedural execution models, ambiguities due to the execution ordering can occur. No global, declarative semantics of referential actions has yet been defined.We show that the well-known logic programming semantics provide a natural global semantics of referential actions that is based on their local characterization: To capture the global meaning of a set RA of referential actions, we first define their abstract (but non-constructive) intended semantics . Next, we formalize RA as a logic program P RA . The declarative, logic programming semantics of P RA then provide the constructive, global semantics of the referential actions. So, we do not define a semantics for referential actions, but we show that there exists a unique natural semantics if one is ready to accept (i) the intuitive local semantics of local referential actions, (ii) the formalization of those and of the local "effect-propagating" rules, and (iii) the well-founded or stable model semantics from logic programming as "reasonable" global semantics for local rules.We first focus on the subset of referential actions for deletions only. We prove the equivalence of the logic programming semantics and the abstract semantics via a game-theoretic characterization, which provides additional insight into the meaning of interacting referential actions. In this case a unique maximal admissible solution exists , computable by a ptime algorithm.Second, we investigate the general case---including modifications. We show that in this case there can be multiple maximal admissible subsets and that all maximal admissible subsets can be characterized as 3-valued stable models of P RA . We show that for a given set of user requests, in the presence of referential actions of the form ON UPDATE CASCADE, the admissibility check and the computation of the subsequent database state, and (for non-admissible updates) the derivation of debugging hints all are in ptime. Thus, full referential actions can be implemented efficiently.

XPathLog is a logic-based language for manipulating and integrating XML data. It extends the XPath query language with Prolog-style variables. Due to the close relationship with XPath, the semantics of rules is easy to grasp. In contrast to other approaches, the XPath syntax and semantics is also used for a declarative specification how the database should be updated: when used in rule heads, XPath filters are interpreted as specifications of elements and properties which should be added to the database. The formal semantics is defined wrt. a graph Herbrand structure which covers the XML tree data model. XPathLog has been implemented in LoPiX.

Deductive object‐oriented frameworks integrate logic rules and inheritance. There, specific problems arise: due to the combination of deduction and inheritance, (a) deduction can take place depending on inherited facts, thus raising indirect conflicts, and (b) also the class hierarchy and ‐membership is subject to deduction. From this point of view, we investigate the application of the extension semantics of Default Logic to deductive object‐oriented database languages. By restricting the problem to Horn programs and a special type of defaults tailored to the semantics of inheritance, a forward‐chaining construction of a Herbrand‐style representation of extensions is possible. This construction is compared with the semantics for F‐Logic (and implemented in the FLORID system) which is based on a combination of classical deductive fixpoints and an inheritance‐trigger mechanism. We show that the F‐Logic semantics coincides with the standard semantics of Default Logic and Inheritance Networks.

Referential actions are specialized triggers used to automatically maintain referential integrity.While their local behavior can be grasped easily, it is far from clear what the combined effect of a set of referential actions, i.e., their global semantics should be.For example, different execution orders may lead to ambiguities in determining the final set of updates to be applied.To resolve these problems, we propose an abstract logical framework for rule-based maintenance of referential integrity: First, we identify desirable abstract properties like admissibility of updates which lead to a non-constructive global semantics of referential actions.We obtain a constructive definition by formalizing a set of referential actions RA as logical rules, and show that the declarative semantics of the resulting logic program PRA captures the intended abstract semantics: The well-founded model of PRA yields a unique set of updates, which is a safe, sceptical approximation of the set of all maximal admissible updates; the thud truth-value undefined is assigned to all controversiaI updates.Finally, we show how to obtain a characterization of all maximal admissible subsets of a given set of updates using certain maximal stable models.-.-.--... .