- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Fri, 18 Feb 2005 11:05:21 +0000
- To: Howard Katz <howardk@fatdog.com>
- CC: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Howard Katz wrote: > Hi Andy, > > What you're saying about EFB is correct. I'm wondering tho what > does it -mean- to AND a ?x variable with something? Can you give > me an example of when you might want to do that? > > Howard Hi Howard - This came up while we were discussing value testing in general. "AND ?x" is the simplest case but the general case is using ?x where a boolean is required (|| &&, not). And in SPARQL, we also have the extension functions which filter (sort of return a boolean); if we make function and casting syntax the same, then we have cases where "AND qn:foo(?x)" can occur as well as builtins like bound/isXYZ. So booleans arise in expressions and "AND ?x" is just the simplest case. In itself, it's probably not a good thing to write but I'd be loath to go round making the grammar exclude things based on the argument of "that's not nice" though. Andy > > > -----Original Message----- > > From: public-rdf-dawg-request@w3.org > > [mailto:public-rdf-dawg-request@w3.org]On Behalf Of Seaborne, Andy > > Sent: Thursday, February 17, 2005 11:13 AM > > To: RDF Data Access Working Group > > Subject: Tests for expressions : boolean effective values > > > > > > > > Today, some of us were puzzling over boolean expressions in > > XQuery/Xpath and how > > they affect SPARQL. We think that the "boolean effective > > values" rules apply in > > constraints and I have checked in some tests into > > tests/data/Expr2 for this. > > > > "boolean effective values" reference: > > http://www.w3.org/TR/xquery/#dt-ebv > > > > and it means that: > > > > "AND ?x" is legal. > > > > ?x is true if the value of ?x is: > > > > * boolean and the value of the boolean is true > > * a string and length(string) > 0 > > * a numeric: number != NaN && number != 0 > > > > Anything else is "type error" which means the whole solution is rejected. > > > > Andy > > > > > > > >
Received on Friday, 18 February 2005 11:06:02 UTC