[xquery-talk] Function for determining one XPath as subset of another
wshager at gmail.com
Wed Jan 27 10:42:59 PST 2016
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
> > 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 is
> not equivalent to /descendant::w).
> > Op woensdag 27 januari 2016 heeft daniela florescu <dflorescu at me.com>
> > volgende geschreven:
> >> >
> >> > It seems to be a long-standing tradition that computer scientists,
> >> > 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
> >> > 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
Lagua Web Solutions
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