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Re: RDF Semantics - Intuitive summary needs to be scoped to interpretations

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 3 Oct 2013 03:01:34 -0500
Message-Id: <D0E403FF-4B83-479E-8763-3635439B61F3@ihmc.us>
To: RDF WG <public-rdf-wg@w3.org>
DRAFT of a reply to David Booth regarding issue 149.  Will be sent in 24 hours if nobody objects. 


David, greetings. This is a response to your email, copied below, which raised issue-149 [1].

We do not agree with your analysis, and do not propose to change the wording of section 5.2, for reasons which I will explain. 

The section in question is intended to provide a very loose, intuitive, non-technical description of what the formal semantics describes exactly. The intuition in question is that graphs have a truth-value which is completely determined by what their component IRIs denote. This is also exactly the intuition underlying the formal model theory, reflected formally by the fact that an interpretation is a function on all IRIs, and that this function completely determines the meanings of all RDF structures larger than a single IRI. The notion of "interpretation" is a mathematical device for expressing the fact that the denotations of IRIs intended by the writer of some RDF may not be known by the reader, and is used to account for the fact that valid inference rules are immune to such communicative disconnects (since validity means that it holds regardless of which interpretation is applied to the IRIs.) 

The avoidance of "interpretation" language in this informal, descriptive, account is deliberate, as is the use of the verb "interpret" to suggest how the formal mathematical account given in the surrounding normative text should be understood to relate to this intuitive, informative, summary. The interpretations mentioned in point 4 are indeed the results of the verb "interpret" in point 2, as you surmise. Readers who see the connection should not be confused by this confluence of naming, which is deliberate. One could describe an interpretation as a "way of interpreting" what IRIs mean. 

Your suggested re-wording would re-introduce the mathematical terminology into the intuitive summary, defeating its purpose. More seriously, it is not in fact correct to say that a graph is true when *there exists* an interpretation, etc.. That wording defines the notion of satisfiability rather than truth. 

For these reasons, we have decided not to change the wording of section 5.2. 

Please reply to public-rdf-comments@w3.org indicating whether this reply is an adequate response to your comment. 

Pat Hayes (for the RDF WG)

[1] https://www.w3.org/2011/rdf-wg/track/issues/149

On Oct 2, 2013, at 12:15 AM, David Booth wrote:

> https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-mt/index.html
> Section 5.2 Intuitive summary needs to be scoped to a particular interpretation or set of interpretations.  At present the interpretations are implicit, and this is misleading because it suggests that the notion of a graph being true is somehow independent of an interpretation, whereas in fact the truth of a graph critically depends on the interpretations that are chosen.
> I suggest rewording the first sentence of this section from: "An RDF graph is true exactly when: . . . " to: "An RDF graph is true exactly when there exists an interpretation such
> that: . . . "
> Also, the verb "interpret" is being used in this clause: "2. there is some way to interpret all the blank nodes in the graph as referring to things,", but that causes confusion with the notion of an interpretation (which is a function).  It would be better to use a different verb at this point.
> Also point 4 mentions "these interpretations", but it isn't clear what interpretations are meant.  Perhaps it means the results of the verb "interpret" in item 2?  In which case, a different word should be used here also.
> Thanks,
> David

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Received on Thursday, 3 October 2013 08:02:08 UTC

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