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Re: Multiple Named Graph

From: Reto Gmür <reto@apache.org>
Date: Wed, 26 Mar 2014 22:32:22 +0100
Message-ID: <CALvhUEUAVFa-Nu_YzLeAQ-_8uGHB=Hs4y0BALZUZUMRotUkHvQ@mail.gmail.com>
To: "henry.story@bblfish.net" <henry.story@bblfish.net>
Cc: Linked Data Platform WG <public-ldp-wg@w3.org>, public-ldp <public-ldp@w3.org>
On Wed, Mar 26, 2014 at 12:29 PM, henry.story@bblfish.net <
henry.story@bblfish.net> wrote:

>
> On 26 Mar 2014, at 10:50, Reto Gmür <reto@apache.org> wrote:
>
>
>
>
> On Tue, Mar 25, 2014 at 10:21 PM, henry.story@bblfish.net <
> henry.story@bblfish.net> wrote:
>
>>
>> On 25 Mar 2014, at 14:59, Reto Gmür <reto@apache.org> wrote:
>>
>>
>> On Tue, Mar 25, 2014 at 2:30 PM, henry.story@bblfish.net <
>> henry.story@bblfish.net> wrote:
>>
>>> So to start from the beginnging again.
>>> I checked the mentions of "named graph" in the spec.
>>>
>>> In the definitions section:
>>> [[
>>> Linked Data Platform RDF Source (LDP-RS) An LDPR<https://dvcs.w3.org/hg/ldpwg/raw-file/default/ldp.html#dfn-linked-data-platform-resource> whose
>>> state is fully represented in RDF, corresponding to an RDF named graph<http://www.w3.org/TR/rdf11-concepts/#dfn-named-graph>.
>>> See also the term RDF Source<http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-source> from
>>> [rdf11-concepts<https://dvcs.w3.org/hg/ldpwg/raw-file/default/ldp.html#bib-rdf11-concepts>
>>> ].
>>> ]]
>>>
>>> Section 5.1:
>>> [[
>>> Alternatively, servers may provide the net worth resource and supporting
>>> containers in a single response representations. When doing this, a
>>> preference would be for RDF formats that support multiple named graphs
>>>
>>
>> If as you quote above, the state of an LDPR is fully represented in RDF
>> why should the preference be to return a format that support multiple named
>> graphs? The latter suggest the resource can be more completely represented
>> using more than just RDF which contradicts the first.
>>
>>
> If a client were to ask for text/n3 then you could give more context back.
> You would not be returning more information about the graph itself, you
> would just be adding more information about the context of other graphs,
> presumably graphs referred to by the graph that was requested. So there is
> no contradiction here.
>

So to make sure I understand: an LDP-RS is fully represented by an RDF
graph. The URI of the LDP-RS together with the RDF graph that represent the
resource form a named graph according to the definition for RDF datasets in
RDF 1.1 (a pair of graph name and a graph). So rather than returning a
graph and LDP server might also return a dataset consisting of a single
named graph with the URI of the requested resource as graph name. LDP
defines (implicitly somewhere) a relationship between the graph name and
the graph (the graph describes the resource identified by graph name) and
allows returning the dataset instead of the graph. Furthermore for
precaching purposes (and extending the current REST architecture) it
suggests that the dataset returned might also contain other graphs which
are not part of the representation of the requested resource but which are
presumably "referred to by the graph that was requested" meaning that the
graph name is a node in the graph that represents the requested resource.
Furthermore, if the client didn't request a format that encodes a dataset
but just wants a graph the LDP server returns the union of all the named
graphs in the dataset - unfortunately the client in this case is not able
to identify the subgraph that fully represents the LDP-RS, that's why the
preference would be the RDF formats that support multiple named graphs. The
novel precaching mechanism is only suggested for graphs, not for other
resources (e.g. using multipart/mime).

Am I getting it right?

Reto


>
>
>
>> I don't agree. You can represent graphs by using datatypes that map
>> strings to graphs. For example one could invent one such as
>> rdf:Turtle .
>>
>>
>> :joe :believes "<http://jane.org/#me> <http://relationship.vocab/loves> <
>> http://joe.org/#i> ."^^rdf:Turtle .
>>
>> RDF semantics allows this to be done. It would allow you to encode graphs
>> in simple RDF formats. Don't forget that
>> in the RDF semantics a datatype is a function from a string to an object.
>> The ones defined by xsd are numbers, binary, date.
>> Nothing stops you from having maps from rdf syntaxes to the graphs they
>> represent.
>>
>> Yes. But it change nothing to the contradiction above.
>
>
>>
>> It would help to understand your positions if you could state your take
>> on Sandro's statements/questions.
>>
>> It still would.
>
> Reto
>
>
> Social Web Architect
> http://bblfish.net/
>
>
Received on Wednesday, 26 March 2014 21:32:49 UTC

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