[xquery-talk] Function for determining one XPath as subset of another

[Christian Grün]

> Well, so, to continue, let's assume that there are no user-defined
> functions, and in fact the only thing we want to proof is select+filter,
> where a filter is limited to the default operators. From that is it follows
> that
>
> -path1:
> select-child-nodes-by-name(select-child-nodes-by-name($context,'x'),'w')
> -path2: select-descendant-nodes-by-name($context,'w')

Just to complete this: The predicate must not be numeric (//w[1]  is
not equivalent to /descendant::w[1]).



> Op woensdag 27 januari 2016 heeft daniela florescu <dflorescu at me.com> het
> volgende geschreven:
>>
>> >
>> > It seems to be a long-standing tradition that computer scientists, when
>> > asked to prove a difficult conjecture C, respond by giving a proof for a
>> > simplified conjecture C'. While this might lead to progress in the long run,
>> > and enables them to get papers published in the academic literature, it is
>> > totally useless to practical engineeers who want to know whether they can
>> > safely rely on C.
>>
>> Michael,
>>
>>
>> what you say is nice and true.
>>
>> However given that:
>> 1. path expressions point (syntactically hence esemantically) into
>> XQuery’s expressions
>> 2. XQuery expression language is Turing complete
>> 3. Subsumption for a Turing complete language is undecidable.
>>
>> Well, I can hardly see a way to decide this problem other then by
>> introducing SOME restrictions
>> of some sort… but of course some restrictions that would not nullify the
>> original problem all together
>> and make the solution useless.
>>
>> Best,
>> Dana
>
>
>
> --
>
> W.S. Hager
> Lagua Web Solutions
> http://lagua.nl
>
>
>
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