URIs in constraints, isBound, casting in eq

I'm studying...

"Definition: Constraints

A constraint is a boolean-valued expression of variables and RDF Terms
that can be applied to restrict query solutions."

I think that should be "and RDF Literals", right?
i.e. 
	AND dc:title < 5
is not a constraint in that sense, is it?

Nor is
	AND dc:title eq dc:creator
is it?


I *think* a constraint is just a boolean function of a solution,
right? i.e. the constraint
	?X < 5
is true of the solution { ?X => 4 } and false for { ?X => 6 }.

Looking at it that way gives a definition for
isBound(expr). Though... isn't isBound always redundant?
Don't all solutions bind all variables?

Also, this scares me:

"The following operators work in any type, and will cast values to
appropriate types before testing: eq, ne"

Design of casting is one of the most time-consuming things a WG
can do. Please strike that or replace it with a very precise
pointer into a mature spec (Java or maybe XQuery) that gives
the casting rules.


ref
http://www.w3.org/2001/sw/DataAccess/rq23/
$Revision: 1.137 $ of $Date: 2004/11/19 17:44:46 $

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
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