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Re: comment on /2001/11/13-RDF-Query-Rules/ re 'single arc languages'

From: Libby Miller <Libby.Miller@bristol.ac.uk>
Date: Tue, 18 Mar 2003 21:39:13 +0000 (GMT)
To: Dan Brickley <danbri@w3.org>
cc: eric@w3.org, www-rdf-rules <www-rdf-rules@w3.org>
Message-ID: <Pine.GSO.4.44.0303182136420.5334-100000@mail.ilrt.bris.ac.uk>

I think Versa might be one of these 'single arc' types - see

and especially


On Tue, 18 Mar 2003, Dan Brickley wrote:

> Eric,
> I'm reviewing http://www.w3.org/2001/11/13-RDF-Query-Rules/
> Rather than try to prepare a single detailed review, I'm sending
> separate msgs on particular bits as and when I grab time to do this. If you'd
> rather I tried to make a more unified review doc, I could do that. The
> current approach seemed a quicker way to make gradual progress...
> So first thing I wanted to ask about:
> Under "Goal Characteristics", you distinguish...
> [[
> graph or arc
>     Some languages express a single arc, others an open subgraph.
>     No observed single arc languages support variables. This
>     leaves them unable to answer the specific query
>     represents(?x ?x) "What lawyers represent themselves?" but
>     instead the more general question represents(?x ?y) "What
>     lawyers represent anybody?". At this point, all single
>     arc query languages are outside the scope of this survey.
> ]]
> This paragraph makes me curious. You rule discussion of these languages
> out of scope, and don't cite any. Are they a theoretical rather than
> actual possibility? In my experience 'single arc' functionality is only
> exposed via RDF APIs, rather than textually represented query languages.
> I don't know of any actual 'single arc' query syntaxes, though perhaps
> some of the path-oriented efforts might fall under this heading?
> Your claim that "No observed single arc languages support variables" would
> carry more oomph if you listed some observed single arc languages. Can you
> give examples? Even if for the purposes of ruling them out of scope for
> detailed analysis. If there aren't any, this is probably worth noting.
> Dan
> ps. you also have "some languages" in the first entry, and "some query engines"
> in the second, under "Goal Characteristics". Are you comparing query
> languages or software designs / implementations? (these have tended to be
> 1:1 in recent history, I guess...). My assumption is that the focus here is
> on language comparison.
Received on Tuesday, 18 March 2003 16:40:44 UTC

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