In this work, a logic-based framework for handling XML data is proposed. XPath-Logic embeds an extension of the XPath query language into first-order logic. We give a model-theoretic semantics of XPath-Logic formulas based on answer-sets. XPathLog is the Horn fragment of XPath-Logic, providing a logic-based language for manipulating and integrating XML data. 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 Herbrand structure which covers the XML data model. XPathLog has been implemented in LoPiX.

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Revised versions can be found in the Habilitation Thesis and in Theory and Practice of Logic Programming, 2004.
Further documentation can be found on the LoPiX project homepage.