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

[W.S. Hager]

Finally, can it be proved that /w[@a=b] is a subset of /w, taking into
account that the filter can only contain standard operators (eq, gt, lt,
etc as defined in the op namespace)?

2016-01-27 17:46 GMT+01:00 Christian Grün <christian.gruen at gmail.com>:

> > 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
> >
> >
> >
> > _______________________________________________
> > talk at x-query.com
> > http://x-query.com/mailman/listinfo/talk
>



-- 

W.S. Hager
Lagua Web Solutions
http://lagua.nl
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