Tree Automata to Verify XML Key Constraints

We address the problem of checking key constraints in XML. Key constraints have been recently considered in the literature and some of their aspects are adopted in XMLSchema. However, only few works have appeared concerning the verification of such constraints. Unranked deterministic bottom-up tree automata can be used to validate XML documents against a schema. These automata work over (unranked) trees used to represent XML documents. In this paper we show how key constraints can be integrated in such automaton by extending the automaton to carry up values from the leaves to the root, during its run. In fact the tree automaton becomes a tree transducer. Under these conditions, the key verification is done in asymptotic linear time on the size of the document.