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Re: [All] Proposal: RDF Graph Identification

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 16 Aug 2012 10:23:32 -0400
Message-ID: <502D0264.6040803@gmail.com>
To: W3C RDF WG <public-rdf-wg@w3.org>
CC: David Wood <david@3roundstones.com>
OK, let me throw out the first counter-proposal.

I find that this document goes quite a bit beyond what I think is necessary or 
desirable to support named graphs.  I propose instead a minimalist version of 
graph identification.  I will describe this minimalist version by stripping 
away pieces of the document.

Major changes:

1/ No mutability:

Mutability is not required for named graphs or graph stores.  To effect this 
change, excise the first part of Section 2, Section 2.1, and Section 2.4.  
Also fix up the abstract and Section 1.

I am somewhat ambivalent about whether the working group should do anything 
about mutability, but I am sure that the working group should not tie 
mutability to named graphs and certainly not to datasets.

2/ Semantic fixes

The document is rather confusing in Section 3.1 where it introduces the 
semantics of datasets.  I would instead just say that the semantics of the 
named graphs in a dataset are not affected by the semantics of the default graph.

I see little to retain in Section 3.2.  I mention two major issues below, but 
there are also some minor problems.  Also the definition of interpretations of 
datasets is rather badly flawed, it probably means to refer to interpretations 
of DG, but I can't tell whether this was just missed or whether some portion 
of the definition was supposed to be this instead.

I don't see why the vocabulary of a dataset should include the RDF 
vocabulary.  Why not just exclude this?  I see no reason make RDF graphs 
disjoint from literal *values*.  If someone wants to create their own datatype 
for RDF graphs, using whatever syntax they dream up, then why not let them?  I 
find it very strange to permit repeated names in a dataset.  Why not just 
require unique names (which is already a condition earlier in the document)?  
Certainly permitting unequal but simply equivalent values is without precedent 
and unsupported.  The possible requirement that graph names not be blank nodes 
or not literals belongs in a syntax section, not in the semantics.

There does not appear to be any observable differences between the 
interpretations for RDF graphs and interpretations for datasets, except if a 
name is used twice, which can lead to inconsistency (even with requirement 2, 
unless identity for RDF graphs is modified to mean mutual simple 
entailment).   In any case, Section 2.2 says that names can't be repeated in 
datasets.  The semantic extension is essentially useless, so should just be 
eliminated.

I suggest instead either saying nothing, or saying that the semantics of an 
RDF dataset is just the semantics of its default graph.


Minor changes:

Whether the name of a named graph can be a blank node is mostly a syntactic 
issue.  Comments about this being a semantic issue should be removed.

The wording in Section 3.1 is rather confused.  RDF Graphs don't have 
"truth".  Instead say "semantics".  Similarly, RDF graphs don't have 
"interpretation", which should also be replaced by "semantics".

peter
Received on Thursday, 16 August 2012 14:24:02 UTC

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