- From: Dan Connolly <connolly@w3.org>
- Date: Wed, 22 Dec 2004 08:43:48 -0600
- To: "Seaborne, Andy" <andy.seaborne@hp.com>
- Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
On Wed, 2004-12-22 at 10:26 +0000, Seaborne, Andy wrote: [...] > ==== Case 2: > > This is a great test case from Steve: > "find all the people with exactly one known email address" > > might be: > > SELECT ?person > WHERE > (?person :email ?e1) > UNSAID { (?person :email ?e2) AND ?e2 NE ?e1 } > > but also optionals+constraints can do it: > > PREFIX : <http://example.org/ns#> > > SELECT ?person > WHERE (?person :email ?e1) > OPTIONAL { (?person :email ?e2) AND ?e2 NE ?e1 } > AND ! &dawg:bound(?e2) > > using the same method Steve had of using optional, then inverting the sense > of the match with dawg:bound. I thought dawg:bound was sort of wishful thinking in an earlier message... I had trouble finding it in the editor's draft... do you mean isBound in 11.2.2? http://www.w3.org/2001/sw/DataAccess/rq23/#sparqlTests "Return true if its argument, which may be an expression, is defined. NaNs and INFs count as defined." Surely the arguments to operators are the *values* of expressions, right? for example "fn:compare Compare two strings.. Returns -1, 0, or 1, according to the rules of the collation used." If I write fn:compare(?x, "abc") it's not comparing the 3-character string "?x" with the 5-character string '"abc"'; rather, it's comparing whatever ?x is bound to with the 3-character string "abc", right? So the specification of isBound has use/mention bugs... operators can't see variable names. isBound would have to be a language keyword, like UNSAID or SOURCE. I'm afraid dtype() has the same problem. I think the safest thing about this issue http://www.w3.org/2001/sw/DataAccess/issues#useMentionOp is to take them out. More related problems... under extensible value testing... "A function can test some condition of bound and unbound variables or constants." I don't see how that makes sense. Functions can't see unbound variables; they can only be evaluated once variables are bound. A function is a mapping of some values to other values. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/ D3C2 887B 0F92 6005 C541 0875 0F91 96DE 6E52 C29E
Received on Wednesday, 22 December 2004 14:43:15 UTC