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> Regarding mathematical properties: in particular, closure properties.
>
> The operations being closed under regular tree languages
> might be desirable property..
XSLT/XPath is closed with respect to its own data model. I don't know
how XSLT's data model relates to a "regular tree language", and I'm not
familiar with notations such as (a^n b^n).
Is there any chance you could translate this into XML terminology for
us?
The examples seem to suggest that your concerns are with queries that
generate a sequence of nodes rather than a single node. Sequences are
part of the data model, and the language is closed over this space.
Michael Kay
>
> 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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