Subject: Re: [xsl] Type of a variable containing values of mixed types From: "Justin Johansson procode@xxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> Date: Tue, 14 Apr 2015 14:22:34 -0000 |
Wow, thank you very much Michael Kay for your thorough and well-thought response. Rumour has it, given your ability to speak-think-and-type, that you must be a machine! Regards, Justin Johansson On 14/04/15 23:35, Michael Kay mike@xxxxxxxxxxxx wrote: > For reasons which I do not claim to fully understand, the XPath/XSD > type system for atomic types is based on the notion of explicit type > labels, rather than being purely predicate-based ... > Having said all that, I think the reasons for making xs:numeric a > union type rather than a base type for xs:double, xs:decimal, and > xs:float were pragmatic: either approach would have worked > technically. Making it a base type would have involved either changes > to XSD, or a divergence between the XSD and XDM type hierarchies, both > of which would have had messy consequences. Introducing a union type, > having done all the groundwork to provide proper support for union > types in general, was much more straightforward. > > Michael Kay > Saxonica > mike@xxxxxxxxxxxx <mailto:mike@xxxxxxxxxxxx> > +44 (0) 118 946 5893 > > > > > On 14 Apr 2015, at 14:25, Justin Johansson procode@xxxxxxxxxxx > <mailto:procode@xxxxxxxxxxx> <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx > <mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote: > >> This question has been on my TODO list to ask the folks at >> MulberryTech XSL List for quite some time. >> >> I think this came about in XPath DM 3.0 regarding xs:numeric as per >> spec ref: >> >> http://www.w3.org/TR/xpath-datamodel-3/#types-hierarchy >> >> In the type hierachy xs:numeric now appears for the first time >> spec-wise (I believe) and it's on the right-hand side under "union >> types". >> >> Mathematically this seems inconsistent with respect to >> xs:anyAtomicType given that it as a diagrammed type itself appears on >> the left-hand side of the type hierarchy diagram and so does not >> identify itself as a union type. But surely xs:anyAtomicType is in >> fact a union type (set-theoretically/type-theoretically speaking). So >> with respect to "union/non-union" reasoning which is correct >> xs:anyAtomicType or xs:numeric as far as the diagram goes? Or, >> rephasing, why is xs:numeric treated somehow differently to >> xs:anyAtomicType? >> >> On the other hand, perhaps this is all to do with some practical >> reason for injecting xs:numeric into the XPath DM 3.0 type hierarchy >> as a union type so as not to disaffect the status quo? >> >> Any thoughts/insight from XSL List community? >> >> Justin Johansson >> >> Twitter: ** b*@MartianOdyssey* <https://twitter.com/MartianOdyssey> : >> Project Clockwork: My invention of the fastest and most extensible >> XPath engine for the JVM (superlatives aspirational).
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