[XSL-LIST Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Function for determining one XPath as subset of a
> On 26 Jan 2016, at 19:29, Wolfgang Laun wolfgang.laun@xxxxxxxxx <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote: > > If you can't prove it: claim it is an axiom ;-) That's exactly what the XQuery formal semantics does, as it happens. For the record, the actual theorem is: for any nodeTest T, the expressions preceding::T and ancestor-or-self::*/preceding-sibling::node()/descendant-or-self::T are equivalent; that is, for any context node, the two expressions deliver the same sequence of nodes as the result. Michael Kay Saxonica > -W > > On 26 January 2016 at 20:24, Michael Kay mike@xxxxxxxxxxxx <mailto:mike@xxxxxxxxxxxx> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote: > I've always been a little frustrated that I rely heavily on equivalences like > > preceding::x === ancestor-or-self::*/preceding-sibling::*/descendant-or-self::* > > without having what I would consider a formal proof. > > Michael Kay > Saxonica > > > > On 26 Jan 2016, at 16:15, Adam Retter adam.retter@xxxxxxxxxxxxxx <mailto:adam.retter@xxxxxxxxxxxxxx> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote: > > > > Given two simple XPaths, say: > > > > 1. //w > > > > 2. /x/y/z/w[@a = 'v'] > > > > As a human I can very easily tell without evaluating the expressions > > that (2) will return a subset (or the same set) of the results that > > (1) would return *should* they both be evaluated. > > > > My goal here is given any two simple arbitrary XPaths expressed as > > strings, and without evaluating them against a context, to determine > > whether one would return a subset of the results of the other. > > > > I wondered if there might be an algorithm or library that someone > > already had or has written which might be able to give me the answer? > > > > I realise that I can only probably cover a subset of XPath itself, but > > it is only the path steps with predicates which I am interested in. > > > > Ideally I am looking for something in Java. > > > > -- > > Adam Retter > > > > skype: adam.retter > > tweet: adamretter > > http://www.adamretter.org.uk <http://www.adamretter.org.uk/> > > > > > XSL-List info and archive <http://www.mulberrytech.com/xsl/xsl-list> > EasyUnsubscribe <-list/293509> (by email <>)
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