Subject: [xsl] Re: Re: order of UNIONs From: Dimitre Novatchev <dnovatchev@xxxxxxxxx> Date: Wed, 14 Nov 2001 21:43:00 -0800 (PST) |
> But does this really make sense? select="group[21]|group[1]" means for me > 'select the 21st group and add the 1st group'. It makes ***perfect sense***. Node-sets are sets. Sets do not have order. Regardless of the order, in which you add elements, the result is the same set: a | b = b | a The above is an axiom in set theory. What you actually need is kinda bag, or list -- these are very different structures from sets. Both allow duplicates, and a list has order. I think one of the major problem of the XPath 2.0 Data Model is that they do not distinguish between lists and sets, trying somehow to say that a node-set is a kind of list (the actual term used there was "sequence", if I remember well). The consequences are bad problems, because some operations on lists cannot be performed 1:1 on sets, and vice versa -- not every list is a set, an operation performed on a sequence, that is a nodeset, may not yield a nodeset, a nodeset operation performed on a sequence that is a nodeset, may behave quite differently from the same operation, performed on a sequence (e.g. eliminating/preserving duplicates on a union/append operation). Cheers, Dimitre Novatchev. __________________________________________________ Do You Yahoo!? Find the one for you at Yahoo! Personals http://personals.yahoo.com XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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