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Regarding mathematical properties: in particular, closure properties. The operations being closed under regular tree languages might be desirable property.. I have seen two kinds of operations under which regular tree languages are not closed.. that is the result is not a regular tree language.. (a) Consider the schema: S -> s (A, S, B) | s () A -> a () B -> b () if we write a query like // (a | b) -- the result is (a^n b^n) which is not regular tree language.. (b) Consider S -> s (A*) A -> a () consider the query for $x in //a return <b/> for $x in //a return <c/> the result is (b^n c^n) The question is has the new constructs in XPath made it not closed or not.. It might have.. If someone has studied these aspects, then we can know if XPath 2.0 is different from XPath 1.0 in these respects also.. cheers and regards - murali.
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