W3C home > Mailing lists > Public > public-rdf-wg@w3.org > July 2013

adding inline graphs to TriG

From: Sandro Hawke <sandro@w3.org>
Date: Tue, 16 Jul 2013 20:53:58 -0400
Message-ID: <51E5EB26.2050802@w3.org>
To: W3C RDF WG <public-rdf-wg@w3.org>
I know this is going to seem to some people like it's going too far, but 
it seems to me like such a good idea, in good conscience I have to at 
least seriously propose it.    If there aren't at least three +1's for 
this email, I wont mention it again.

Right now, in TriG, you can say things like:

    [ a :Patch;
       :deletes _:g1;
       :inserts _:g2 ].
    GRAPH _:g1 { ... }
    GRAPH _:g2 { ... }

I think it would make a whole lot of sense to allow a little syntactic 
sugar.  I'd like to allow this:

    [ a :Patch;
        :delete { ... };
        :inserts { ... } ].

The mechanism for this would be exactly like the mechanism for 
square-bracket [ ... ] expressions.  Just like [ ... ] is syntactic 
sugar for a blank node that is "used" once, inline graphs would be 
syntactic sugar for a named graph that is "used" once.    Any TriG 
document with inline graphs could be re-written to not have inline 
graphs by just replacing the inline graph with a new blank node label, 
then adding to the end of the document a name-graph pair of that label 
and that graph.     Nested inline graphs work fine by this rule, with no 
special handling.

For example:

    :alice :said { :bob :said { :charlie said { :spot a :Dog } } } }

is syntactic sugar for:

    :alice :said _:u1.
    GRAPH _:u1 { :bob :said _:u2 }
    GRAPH _:u2 { :charlie said _:u3 }
    GRAPH _:u3 { :spot a :Dog }

I'm unsure about whether to allow this in the subject position or just 
the object position.  It's probably hard to parse in the subject 
position; I'm not sure it can be done with an LL(1) grammar.   (Consider 
that "{s p o} s p o" is currently valid TriG, distinguishing that from 
"{s p o} p o" is tricky.)   I don't think it's hard in just the object 
position, and most of my use cases are fine with the object position.  
If people like this idea in general, I'll investigate the grammar more.

People familiar with N3 will note this makes TriG even more like N3.  
I'd say it brings TriG from being 85% of N3 to maybe 95% of N3.  This is 
probably a good thing.   (I'm measuring in terms of feature 
usage/importance, and excluding features that are really just RDF 
vocabulary.)

So, anyone else think it's worth fully spec'ing this and adding it as a 
TriG "Feature At Risk" for last call?

If not, I can just put it on my wishlist for the next turtle-like 
dataset syntax, someday.

       -- Sandro
Received on Wednesday, 17 July 2013 00:54:11 UTC

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