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Abstract: We investigate the typechecking problem for XML transformations: statically verifying that every answer to a transformation conforms to a given output schema, for inputs satisfying a given input schema. As typechecking quickly turns undecidable for query languages capable of testing equality of data values, we return to the limited framework where we abstract XML documents as labeled ordered trees. We focus on simple top-down recursive transformations motivated by XSLT and structural recursion on trees. We parameterize the problem by several restrictions on the transformations (deleting, non-deleting, bounded width) and consider both tree automata and DTDs as input and output schemas. The complexity of the typechecking problems in this scenario ranges from to . [Copyright &y& Elsevier]

We define a new logic-based query language, called DAC, which is an extension of Datalog. A DAC(w(n),h(n))(b(n))-program consists of a family of Datalog programs Pn such that w(n),h(n),b(n) bound the width of rules, the number of rules, and the recursion depth of any Pn, respectively. We exhibit queries which are not Datalog expressible but are DAC expressible. We also prove non-expressiveness results for DAC and we infer various strict hierarchies obtained by allowing more rapidly growing functions on the bound parameters. [Copyright &y& Elsevier]