Re: Proposal for ISSUE-32, curly braces in joinCondition

Hi Richard and David,

Just curious, and apologies if I'm missing the context from weekly
discussions that may have covered this, but isn't there also the issue of
the various *types* of joins to consider?  I see from one of the spec drafts
(excerpt below) that this issue actually also proposes support for only
simple SQL expressions, as opposed to the original "the join condition may
be as complex as allowed by SQL".  Has it already been decided to support
only equality (inner) join syntax, or is that an implied part of what you're
discussing?  If that decision has not yet been made, then it seems like this
issue really has 3 aspects:

1) curly braces / referencing mechanism
2) multiple columns (or parts) in join clause
3) types of joins - inner, outer, left outer, right outer, ...

If all 3 have to be supported, then some form of string with embedded
table.column references may be the simplest.  (Basically, something similar
to what's there now, just address whatever issues are with the curly
braces).

If only simple joins are to be supported now, then forget all of the above.
:-)

Bob

-------------------------------
From
http://www.w3.org/2001/sw/rdb2rdf/r2rml/#RefObjectMapClass_joinCondition_Property
:

Note that the join condition may be as complex as allowed by SQL.

ISSUE-32 <http://www.w3.org/2001/sw/rdb2rdf/track/issues/32>: The snytax of
rr:joinCondition is still under discussion. It has been suggested that it
should not use curly braces to delimit the logical tables. It has also been
suggested that instead of arbitrary SQL, only simple equality expressions
should be allowed.




On Tue, May 10, 2011 at 4:41 PM, Richard Cyganiak <richard@cyganiak.de>wrote:

>
> On 10 May 2011, at 21:32, David McNeil wrote:
> > If you're violently opposed to lists, then how about the last option I
> mentioned:
> >
> >  [] rr:parentTriplesMap <#TriplesMap1>;
> >     rr:join "col1,col1", "col2,col2";
> >
> > This keeps the columns that are being checked *very* close to each other
> ;-)
> >
> > Indeed. I didn't notice the first time I read this that you put the two
> col1's together in this notation. So the first value always refers to the
> child table? Seems a bit too obscure for my taste.
>
> Fair enough -- it's not very explicit.
>
> Let me do one more try:
>
>  [] rr:parentTriplesMap <#TriplesMap1>;
>    rr:joinChildParent "col1=>col1", "col2=>col2";
>
> Or maybe
>
>    rr:joinFromTo "col1=>col1", "col2=>col2";
>
> Any better?
>
> Richard
>