- From: Costello, Roger L. <costello@mitre.org>
- Date: Wed, 13 May 2009 09:03:50 -0400
- To: "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
> > (Paraphrasing) By allowing the XPath in an <assert> element > > to reference ancestors, cousins, and siblings it will break XPath. > > I don't recognize or recall the comment that you claim to be > paraphrasing. I interpreted the following statement from Michael Sperberg-McQueen as meaning "Allowing XPath expressions to reference ancestors, cousins, and siblings will break XPath": Even if it could be shown that the downward-only restriction on assertions caused a loss in expressive power, it might nevertheless be plausible to argue that the cost in expressive power is outweighed by other factors. In the absence of any demonstrable loss of expressive power, I predict that the compatibility issue for XPath 2.0 and related specs is a clinching argument: on the one hand, we can be compatible with XPath 2.0 et al., or on the other, we can be incompatible in a way that provides, as far as we know, some greater convenience but no additional expressive power. Even if the incompatibility provided some gain in expressive power, many people would turn down that choice because the cost of incompatibility with XPath is very high. But without any gain in expressive power? I think the inconvenience of downward-only assertions is minuscule compared to the inconvenience of having to rewrite XPath 2.0 and the accompanying specs, or of having an incompatibility that makes XSD 1.1 unusable for them. In particular, these words led me to my interpretation: "incompatibility with XPath" and "inconvenience of having to rewrite XPath 2.0" How is it that an XPath expression referencing ancestors, cousins, and siblings in an <assert> element is incompatible with XPath 2.0? And would require rewriting XPath 2.0? /Roger
Received on Wednesday, 13 May 2009 13:04:26 UTC