Re: Question about number types

On 4 Jul 2008, at 19:06, C. M. Sperberg-McQueen wrote:
[snip]
> My earlier answer pointed to passages in the 1.0 and 1.1 specs,
> but on reflection I think the stronger argument is just:  given
> that several of the value spaces are described in the same terms
> (numbers, bit strings), how could the rule that the value spaces
> of the XSD types are disjoint be taken any other way than as
> specifying that they are treated as disjoint for purposes of the
> comparison operations defined in the XSD spec for purposes of
> bounds checking, enumerations, and identity constraints?

If one interprets the XSD type system as having named, not merely  
structural types, then when one adopts the XSD type system (or tries  
to) one imports that aspect as well.

See:
	http://thid.thesa.com/thid-0513-0671-th-0683-5303
	http://en.wikipedia.org/wiki/Structural_type_system
	http://en.wikipedia.org/wiki/Nominative_type_system

This is how I read it. Since OWL basically treats the XSD type system  
*as* a type system (including adopting portions of its definitoin  
system), it seems a reasonable choice to respect those constraints.

>   It
> does not lie within the power of the XSD spec, or any other
> spec, to say that numbers expressible with finite decimal
> numerals and numbers which can be expressed as m  2^e cannot
> be compared.

But that's a slide. Of course you don't say anything like that. But  
it seems XSD *does* say that xsd:float is disjoint with xsd:decimal.  
If we use *those types* (which we explicitly do), shouldn't we  
recognize that aspect of them?

> The disjointness of the value spaces postulated by XSD is a
> convenient way of handling the relatively few cases of
> cross-primitive comparison that can arise in schema-validity
> assessment, and of ensuring that one can postulate, given
> a value, knowledge of its primitive datatype.

That intention isn't determinable from the spec, so I don't see that  
you can rely on people treating the disjointness as a mere convenience.

(The comments in the spec about implementation seems, again, to be  
different from the issue of what is the nature of the type system. I  
can implement a structural types system in a language with a  
nominative type system. The question here is what are the right  
answers from the perspective of the *XSD type system*.)

Cheers,
Bijan.

Received on Friday, 4 July 2008 18:23:35 UTC