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Re: Blank Node Identifiers and RDF Dataset Normalization

From: Steve Harris <steve.harris@garlik.com>
Date: Tue, 26 Feb 2013 18:28:15 +0000
Cc: public-rdf-wg@w3.org
Message-Id: <B703081D-D3B3-4E9D-A60E-AA27C1F11597@garlik.com>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
On 2013-02-26, at 17:46, Andy Seaborne <andy.seaborne@epimorphics.com> wrote:
> On 26/02/13 16:36, Kingsley Idehen wrote:
>> On 2/26/13 6:53 AM, Steve Harris wrote:
>>> On 2013-02-26, at 11:21, William Waites <wwaites@tardis.ed.ac.uk> wrote:
>>> 
>>>> On Tue, 26 Feb 2013 11:10:55 +0000, Steve Harris
>>>> <steve.harris@garlik.com> said:
>>>> 
>>>>> Yes, but this can only happen if you merge multiple datasets,
>>>>> right? Otherwise no-one gets to write anything into the "default
>>>>> graph" against the will of the dataset maintainer.
>>>>> This is related to the reason why I find the idea of having a
>>>>> single format that can express both Graphs and Datasets so scary
>>>>> - you can bring this kind of situation on yourself without any
>>>>> prior warning. Very bad idea.
>>>> I agree, but this arises from the existing of a special graph called
>>>> default and the somewhat non-standard use of the word "default". A
>>>> longer but more accurate name might be, the "graph that cannot be
>>>> named or referred to of which there is only one where we put triples
>>>> that we can't think of a better place to put".
>>>> 
>>>> This could easily be solved by putting
>>>> 
>>>>    default_graph = http://some.name/graph
>>>> 
>>>> in your sparqlserver.ini file and then manage the contents of that
>>>> named graph whatever way you see fit.
>>>> 
>>>> We do not need the notion of "default graph" in the core RDF specs! It
>>>> is a mistake. Please let us get rid of it.
>>> I agree wholeheartedly, and argued quite vociferously against it's
>>> inclusion in SPARQL 1.0, but I think it's too late now. The anonymous
>>> genie is out of the bottle.
>>> 
>>> - Steve
>>> 
>> 
>> As implementers of SPARQL compliant stores and DBMS engines, we (you,
>> Andy, I and others) do have the ability to conjure up our own best
>> practices which could then cycle back to the next round of RDF and
>> SPARQL specs related revisions. It's happened in the past, so why not
>> handle this matter the same way?
>> 
>> Conclusion: We discourage the use of anonymous default graphs in our
>> respective products. Every useful thing should be denoted using an
>> identifier.

4store and 5store out of the box have the "default graph" set to the RDF Union of the named graphs, and I don't know of any installations that have changed that config option, however…

> Jena users find the default graph concept useful:
> 
> 1/ When there is one graph being published
> 
> 2/ As the union of the named graphs
> 
> 3/ As a single place to put the manifest
> 
> Conclusion: you don't have to use it if you don't want to.
> 
> (all well worn points)

Right, if people are genuinely finding it useful, I don't think it's reasonable to ask for it to be removed.

1-3 above /could/ be handed perfectly well in other ways, in a pure quad system. However, they weren't. C'est la vie.

- Steve

-- 
Steve Harris
Experian
+44 20 3042 4132
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80 Victoria Street, London, SW1E 5JL
Received on Tuesday, 26 February 2013 18:28:44 GMT

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