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RE: XQuery value comparisons (Part I - numerics)

From: Howard Katz <howardk@fatdog.com>
Date: Thu, 21 Apr 2005 07:41:24 -0700
To: "Eric Prud'hommeaux" <eric@w3.org>
Cc: "RDF Data Access Working Group" <public-rdf-dawg@w3.org>
Message-ID: <JMEJKDCPGHHIANHOMPDBEEHDCNAA.howardk@fatdog.com>

 > -----Original Message-----
 > From: public-rdf-dawg-request@w3.org
 > [mailto:public-rdf-dawg-request@w3.org]On Behalf Of Eric Prud'hommeaux
 > Sent: Thursday, April 21, 2005 12:06 AM
 > To: Howard Katz
 > Cc: RDF Data Access Working Group
 > Subject: Re: XQuery value comparisons (Part I - numerics)

   [ snip ... ]

 >   declare namespace test = "http://foo.example/"
 >   define function test:imafloat($num as xs:float) as xs:boolean {
 >       return $num instance of xs:decimal
 >   }
 >
 > will see the argument as a float in the function regardless of its
 > lineage.
 >
 >   test:imafloat(xs:decimal(5)) => false
 >
 > Conversely, subtype substitutions retain their origonal type:
 >
 >   define function test:imapostitiveInteger($num as xs:integer)
 > as xs:postitiveInteger {
 >       return $num instance of xs:postitiveInteger
 >   }
 >
 >   test:imapostitiveInteger(xs:postitiveInteger("true")) => true
 >
 >
 > Having framed this, does XQuery-instance-of pay attention to the type
 > tree? I.E., does
 >   xs:postitiveInteger("true") instance of xs:integer
 > return true or false?

Neither: it throws a type exception on the cast (or construction, which ever
way you want to look at it): "can't convert string 'true' to integer".
However if you said (and I know this is what you intended :-),

     xs:positiveInteger(xs:boolean("true")) instance of xs:integer

you'd get a true, because xs:positiveInteger is a subtype of xs:integer. So
yes, "instance of: " pays attention to the tree (which means that your two
functions above aren't testing type promotion vs subtype substitution but
rather the type-tree awareness of instance of.

Howard
Received on Thursday, 21 April 2005 14:41:32 GMT

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