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Re: Comments on RDF Spaces document

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 30 May 2012 10:19:54 +0100
Message-ID: <4FC5E63A.1070807@epimorphics.com>
To: public-rdf-wg@w3.org

On 30/05/12 02:42, Pat Hayes wrote:
> On May 28, 2012, at 8:01 AM, Andy Seaborne wrote:
>> On 28/05/12 13:11, Ivan Herman wrote:
>>>> I don't see why. The only spec that has any reason to mention
>>>> quads is N-Quads. (Well, JSON-LD may too but it uses a
>>>> definition that's different from Sandro's.) Other uses of quads
>>>> are implementation strategies and those don't belong into the
>>>> specs.
>>> Correct. My question was whether this WG would define NQuads as
>>> well or not. If we do define NQuads (and I do not believe this
>>> has been decided pro or con) then we have to properly define
>>> Quads and that in relations to any formalism we have on named
>>> graphs. If we decide that NQuads are not to be formally defined
>>> by this WG, then indeed this section may become unnecessary.
>>> Ivan
>> Firstly, I think we really ought to define N-Quads; it's in use and
>> extending the N-Triples work to N-Quads is valuable.
>> Secondly, it does not mean we have to give quads as first class
>> items in the extended data model.
>> N-Quads-the-format can be defined by:
>> <s>  <p>  <o>  <g>  .
>> is just a way of saying triple<s>  <p>  <o>  in space<g>.
> Do we have to say that last part? Why not just define quads and leave
> it at that? (What is a "space" exactly? Do spaces have a semantics?
> Is my space the same kind of space as your space? Etc..)

(Aside: I don't relate to the word "spaces" very much but its because 
they evoke ideas of continuous functions to me and seems rather 
abstract; a criticism of semweb is that it is too abstract.  Containers 
seems more concretely useful, but if it works for enough people, so be it.)

It could be done with quads (+ the empty set)

There are two issue I see:

1/ If we have quads and datasets, we have to keep two definition stacks 
in step.  We already have datasets from SPARQL.

2/ You point out that the empty graph has no information but it does 
indicate existence and it does happen for real.  <rdf:RDF></rdf:RDF> (or 
the empty file for N-triples but I couldn't write that clearly :-)

So not very interesting but a dataset with { ( IRI, empty set of 
triples) } needs an explanation. A quads-only approach has to introduce 
special cases.

3/ of 2:
Quads vs triples does confuse some people sometimes (this is not common, 
but does come up).  "Why can't I put a quad in a graph [container]?" 
Quads are so like triples, the container metaphor can lead to wanting to 
put quads in boxes ... or spaces.


> Pat
>> That fits nicely into the way Turtle use state variables to explain
>> parsing.
>> We do not strictly need to define a quad and then define how it is
>> associated with a graph pair - just do it in one step.
>> It's a matter of simplicity - if quads are defined as a first class
>> concept, we have to keep the dataset-based part of the specs in
>> step with the quads-based parts (e.g. the empty graph case) .  c.f.
>> MT and the rules.
>> SPARQL Query does not mention quads.
>> SPARQL syntax does for update (it's a rule name in the grammar)
>> SPARQL Update uses this as explanation for templates in the form {
>> ... GRAPH .... } and constructs a dataset out of them.
>> The definition of Graph Store doesn't mention quads.
>> Andy
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Received on Wednesday, 30 May 2012 09:20:24 UTC

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