Abstract
The article introduces a simple framework for the specification of constraints for XML documents in which constraints are specified by (1) a mapping that extracts a relation from every XML document and (2) a relational constraint on the resulting relation. The mapping has to be generic with respect to the actual data values and the relational constraints can be of any kind. Besides giving a general undecidability result for first-order definable mappings and a general decidability result for MSO definable mappings for restricted functional dependencies, the article studies the complexity of the implication problem for XML constraints that are specified by tree pattern queries and functional dependencies. Furthermore, it highlights how other specification languages for XML constraints can be formulated in the framework.
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