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Re: DISTINCT()

From: Olivier Corby <Olivier.Corby@sophia.inria.fr>
Date: Wed, 14 Mar 2012 14:44:48 +0100
Message-ID: <4F60A0D0.8080508@sophia.inria.fr>
To: public-rdf-dawg@w3.org
I fear that the design is becoming over complex.

We used to have two kinds of repetitions:

+ *   without loop in the path (except first step of + ...)
{n,m} with loop in the path

Now we would have three kinds of repetitions:

+ *     without loop, without duplicate
{+} {*} without loop, with duplicate
{n,m}   with loop with duplicate

In addition, {} notation is (in general) used for set but {+} enables 
duplicates so it is misleading
In addition {n,m} and {+} do not behave the same with loops, so it is 
not uniform


(By the way, our experience in my team is that loops in {n,m} are not 
welcome because very often {1,n} is used to limit the length of paths 
wrt +, but unfortunately paths are then trapped into loops (use case 
with symmetric relation, e.g.  foaf:knows{1,5}))


Concerning distinct, I am able to prototype distinct as a global 
operator on path expression:
?x distinct(path) ?y

I would support this design.

Olivier
Received on Wednesday, 14 March 2012 13:45:25 GMT

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