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 <[email protected]>: > > 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 <[email protected]> > 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 > > > > > > > > _______________________________________________ > > [email protected] > > http://x-query.com/mailman/listinfo/talk > -- W.S. Hager Lagua Web Solutions http://lagua.nl
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