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Re: multiple-graph example in the Primner

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Sat, 07 Dec 2013 09:54:36 -0500
Message-ID: <52A336AC.8000707@openlinksw.com>
To: public-rdf-wg@w3.org
On 12/7/13 8:28 AM, Sandro Hawke wrote:
> Kingsley Idehen <kidehen@openlinksw.com> wrote:
>> On 12/7/13 7:54 AM, Sandro Hawke wrote:
>>> Pat, I agree with you about the situation except I believe there's a
>> way out, which is why I stopped objecting back when we were making
>> these decisions.  The way out is to define some vocabulary which
>> communicates from Alice to Bob what kind of dataset semantics Alice is
>> using.   That vocabulary doesn't need to be defined in a W3C
>> recommendation to work.  So the primer just needs to posit that such
>> vocabulary might exist, and give the example as a hypothetical.
>> Alternatively, we could define that vocabulary (non rec track) right
>> now and use it in the primer with a caution that this is only one of
>> many possible ways to use datasets.
>>>        - Sandro
>> Yes, a vocabulary can be used to solve the problem. Net effect, we
>> still
>> don't need a confusing and contradictory example in the spec :-)
> I don't see any need for it to be confusing or contradictory.  I'd suggest we choose the semantics where URLs used as graph names denote sources which yield the associated graph.   I believe that's what the overwhelming majority of readers will expect, so when they read the example they will feel reassured that they can do what they expected.   The only confusing thing will be our caveats, if we're not careful.
>    - Sandro
The following examples will lead to confusion:

## Relative Resource URL serving as a Named Graph IRI
{<#s> <#p> <#o> } .

## variation of the above

{<#s> <#p> <#o> } .

## Absolute Resource URL serving as a Named Graph IRI

{<#s> <#p> <#o> } .

## 3 Named Graphs where two are derived from Resource URLs and one is an 
inferred Default (or System) Named Graph which maybe be associated with
## {<#s> <#p> <#o> } .
## OR
## a Union of the Default, <.ttl>, and <> .

{<#s> <#p> <#o> } .
{<#s> <#p> <#o> } .

All of the examples above cover implementation and usage scenarios that 
are best covered via related specs such as SPARQL (for querying) and 
concrete syntaxes (NQuad, TriG etc.).

It is best for the RDF spec, primer, and related collateral to focus on 
RDF semantics for triples based structured data representation. All 
examples should be simple for the reader to understand and follow :-)

>> Kingsley
>>> Pat Hayes <phayes@ihmc.us> wrote:
>>>> On Dec 5, 2013, at 4:53 AM, Guus Schreiber <guus.schreiber@vu.nl>
>>>> wrote:
>>>>> In the telecon yesterday there were some flames about the graph
>>>> metadata examples in the Primer.
>>>>> My position:
>>>>> - There needs to be at least one example triple in the Primer in
>>>> which a graph name is being used. Dropping this completely is for
>> the
>>>> editors a no-go.
>>>> Including such an example is a no-go for me. I will formally object
>> (or
>>>> protest, or register a dissent, I am not sure of the exact W3C
>> process
>>>> involved here) if the WG publishes any document which implies that
>> such
>>>> usage is in any way supported by the RDF 1.1 specifications. That is
>>>> *exactly* the semantic stumbling-point at which we were unable to
>>>> provide any semantics for datasets. RDF 1.1 does NOT imply in any
>> way
>>>> that the use of a graph-name in an RDF triple can or should be
>>>> understood to refer to the graph. On the contrary, it explicitly
>> denies
>>>> the validity of such an assumption.
>>>>> - We are happy to consider other examples. Please suggest.
>>>>> - We're happy to include other/updated caveats
>>>>> Current phrasing included below. Text suggestions very much
>>>> appreciated!
>>>>> Guus
>>>>> From
>> https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-primer/index.html#subsection-multiple-graphs
>>>> :
>>>>> [[
>>>>> We can write down triples that include a graph name, for example:
>>>>>    <http://example.org/bob> <is published by> <http://example.org>.
>>>>>    <http://example.org/bob> <has license>
>>>>>        <http://creativecommons.org/licenses /by/3.0/>.
>>>>> These two triples could be interpreted as license and provenance
>>>> information of the graph http://example.org/bob.
>>>>> NOTE
>>>>> RDF does not define the way in which the graph name and the graph
>> are
>>>> related. It is therefore up to application developers to decide how
>> to
>>>> interpret such triples.
>>>> That does not deal with the central difficulty. RDF is intended for
>> use
>>>> in publishing data on the open Web. The issue involved here is, if
>>>> Alice publishes an RDF dataset, and Bob reads it, how can Bob know
>>>> whether a graph name used in RDF in the datset should be interpreted
>> as
>>>> referring to the graph it names? And the clear, unambiguous answer
>>>> given by our RDF specs is, Bob cannot know this. There is no way
>>>> specified to record or transmit this information through RDF or any
>>>> means usable by an RDF engine. Alice might conform to the metadata
>>>> useage needed by PROV, and Bob might read this and interpret it
>>>> differently, without failing in any way to conform to RDF. So as far
>> as
>>>> RDF is concerned, this usage is invisible. Vague references to
>>>> "application developers" does not deal with this issue.
>>>> Pat
>>>>> ]]
>>>> ------------------------------------------------------------
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>>>> (preferred)
>>>> phayes@ihmc.us       http://www.ihmc.us/users/phayes



Kingsley Idehen	
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OpenLink Software
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Received on Saturday, 7 December 2013 14:54:59 UTC

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