Re: 3.6 Optional Match

On Wed, Aug 04, 2004 at 09:54:10 -0700, Bob MacGregor wrote:
> BRQL should be commended in adding the OPTIONAL
> clause.  However, I see two problems.  First is that it doesn't
> support nested optional matches (their document acknowledges
> this issue).  Second, BRQL makes a distinction between
> WHERE and AND restrictions.  Both of these should be
> allowable in the OPTIONAL clause, but they aren't (as far
> as I can tell). 

I disagree with this for a number of reasons, first, I think AND is
helpful for readability and familarity to SQL users, and I dont think that
optional AND makes sense in many examples, eg:

a)	SELECT ?x
	WHERE (<foo>, <bar>, ?x)
	OPTIONAL (?x, <math:greater-than>, 120.0)

is equivalent to

b)	SELECT ?x
	WHERE (<foo>, <bar>, ?x)

as far as I can see.

c)	SELECT ?x, ?y
	WHERE (<foo>, <bar>, ?x)
	OPTIONAL (?x, <math:greater-than>, ?y)

is different to b), but I'm not sure what it would be useful for in
real-world examples, and it would infact be quite dangerous to allow
queries of this sort.

- Steve