- From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
- Date: Mon, 14 Feb 2005 09:58:44 +0000
- To: "'RDF Data Access Working Group'" <public-rdf-dawg@w3.org>
On Mon, Feb 14, 2005 at 03:58:33AM -0500, Eric Prud'hommeaux wrote: > > > AND is a special keyword that starts constraints (SUCH THAT would be better > > > but its two words). > > As English words go, WHERE is my personal favorite: > { (?part g:id ?id) > (?part g:od ?od) WHERE ?id < ?od > (?part p:name "nut") } > It's nice for mathematicians. Its fits more closely to SQL semantics too, in my opinion, but its used. SUCHTHAT would be OK. > Using the []s syntax is more pleasing to my eyes: > { (?part g:id ?id) > (?part g:od ?od) [?id < ?od] > (?part p:name "nut") } It just doesnt look like a constraint to me. > > > > Currently in the grammar it is required because ?x-?y > > > is unclear : can be "?x binary minus ?y" or two expressions "?x" then > > > "unary minus ?y" > > > > > > Proposal: use [] to mark constraints (see below). > > > > I dont like this very much. [] has lots of uses in syntax and programming > > langages, but none of them relate to contraints in my experience. > > I think the important one is XPath. > <xsl:for-each select="/root/element[@foo='bar']"/> Isn't that with special ref. to attributes? I think CSS has something similar. I remember it as being like an associative array. > > > [Not sure about typing of function returns which might be lost in such a > > > scheme. Does it hurt optimization?] > > > > I dont think so. Maybe makes it a bit harder, but its allready seriously > > hard. > > I guess every dynamic constraint will be expressed in SQL as a set of > value pattern constraints. Wow, I hadn't even gone there. I susepct I'm missing something, dynamic constraint? > > >From before SELECT seems fine, its the other way round in SQL, but the SQL > > FROM is very different. OTOH I prefer LIMIT at the end, as its parallel > > with SQL is direct. > > > > Incidentally, I dont think of LIMIT as modifying SELECT, I think of it as > > modyfying the result set. > > I think the same is true in SQL. LIMIT and GROUPing aren't in > relational calculus. I bet SQL defines a solution as the result of > LIMITing/GROUPing/COUNTing performed after the relational part is > done. Anyone know where I can get a copy of, say, the SQL 92 spec? How else would I get to sleep at night? http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt Its not the final published form, but its very close IIRC. - Steve
Received on Monday, 14 February 2005 09:58:46 UTC