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Re: Well Behaved RDF - Taming Blank Nodes, etc.

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Thu, 13 Dec 2012 10:35:54 +0000
Message-ID: <50C9AF8A.8090607@epimorphics.com>
To: semantic-web@w3.org
Promoting well-formed lists would be good.

On the datatypes, how about encouraging use of the canonical form of the 
literal as a step towards value-based, rather than datatype based, data:

"1"^^xsd:integer not "+0001"^^xsd:integer

and maybe ideally only xsd:integer and xsd:decimal, not the other 
derived types.

The restriction of "no labels" is not just about "no cycles" - it's 
things that are not tree-like:

:x1 :p _:a .
:x2 :q _:a .


On 12/12/12 19:09, David Booth wrote:
> On Wed, 2012-12-12 at 09:43 -0800, Pat Hayes wrote:
>> On Dec 12, 2012, at 9:01 AM, David Booth wrote:
> [ . . . ]
>>>   A Well-Behaved RDF graph is an RDF graph that can be serialized
>>>   as Turtle without the use of explicit blank node identifiers.
>>>   I.e., only blank nodes that are implicitly created by the
>>>   bracket "[ ... ]" or list "( ... )" notations are permitted.
>> That is too restrictive. There is a real need to be able to describe
>> things such as "Joe's father" or "a woman in a red dress" which are
>> naturally phrased as bnodes with identifying descriptors attached to
>> them.
> Perhaps, for some RDF authors.  And those authors could use full RDF
> instead of the Well Behaved RDF profile.  But according to
> http://web.ing.puc.cl/~marenas/publications/iswc11.pdf
> the vast majority of RDF documents (over 98% of their samples) use blank
> nodes in non-problematic ways.  (I.e., they contain no blank node
> cycles, and thus do not cause the graph isomorphism complexity problem.)
> At present the many applications that process RDF have to pay for the
> sins of those (very) few RDF graphs that use blank nodes in problematic
> ways.
> Actually, it would be interesting to examine whether those <2% of graphs
> that did have blank node cycles really needed them.  My suspicion is
> that the authors could have simply minted a few URIs to break those
> blank node cycles and turn them into non-problematic blank node trees.
> In the nearly 4 million RDF documents Mallea, Arenas, Hogan, and
> Polleres examined, the maximum blank node treewidth they found was 7,
> which I think (though a graph theory expert would have to confirm) that
> only 6 URIs would have to have been minted to turn it into a tree.
Received on Thursday, 13 December 2012 10:36:24 UTC

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