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Re: [Moderator Action] RDF Semantics - Intuitive summary needs to be scoped to interpretations

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 4 Oct 2013 11:31:51 -0500
Cc: W3C RDF WG <public-rdf-wg@w3.org>
Message-Id: <5B207153-17F9-4ECB-87C5-156E59CD4D7B@ihmc.us>
To: Ivan Herman <ivan@w3.org>
I am at a loss how to respond to David on this issue. He is objecting to the style of an informative section whose purpose is to give an short intuitive summary, deliberately using non-technical language, of what the technical model theory is saying. David wants me to use the formal language in this section, which would defeat its point completely. His suggested rewordings do not make sense, as they mention the technical concept but then do not refer to it in any way, which is both puzzling and poor expository style.  I know, from extensive off-line email discussions with David, that he does not properly understand the intuitive foundations of semantics in any case, so I am not inclined to accept his rather condescending advice.

I know it is inappropriate to debate or respond point-by-point at this stage on the public comments list, but I do not see how to deal with this kind of inanity without doing so. I have inserted my own responses to David inline in the following, but obviously have not sent this as a WG response. 

If you or anyone else in the WG can suggest how best to proceed in such a case, I would be grateful.

Pat

On Oct 4, 2013, at 2:32 AM, Ivan Herman wrote:

> Forwarding
> 
> 
> 
> Begin forwarded message:
> 
>> From: David Booth <david@dbooth.org>
>> Subject: [Moderator Action] Re: RDF Semantics - Intuitive summary needs to be scoped to interpretations
>> Date: October 4, 2013 05:46:56 GMT+02:00
>> To: Pat Hayes <phayes@ihmc.us>
>> Cc: RDF WG <public-rdf-wg@w3.org>
>> 
>> Hi Pat,
>> 
>> On 10/03/2013 10:32 PM, Pat Hayes wrote:
>>> David, greetings.
>>> 
>>> This is a response to your email, copied below, which raised
>>> issue-149 [1].
>>> 
>>> The section in question is quite explicit that it is intended to
>>> provide an 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.
>> 
>> Right, but "what their component IRIs denote" is determined *solely* by the interpretation that is applied.  You cannot leave out or gloss over the importance of interpretations.  They are absolutely central to the RDF Semantics.

The formal notion of interpretation is a mapping from IRIs to their denotations. Therefore, "what the IRIs denote" and "interpretation that is applied to the IRI" are virtually synonymous. Which is the point of giving this non-technical gloss, to help readers who do not find it natural to think in terms of mathematical mappings on IRIs. 

>> 
>>> 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.
>> 
>> Yes, exactly.  This notion of an interpretation is absolutely central to understanding the RDF Semantics.  An intuitive introduction must not omit or gloss over it.

This is not an introduction, it is a brief sketchy re-statement of the truth conditions (given in the immediately preceding sections) in non-technical language, as an aid to intuition. 

>> 
>>> 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.)
>> 
>> [Hmm, not relevant to this issue, but it's interesting to see that you have noted that the denotations of IRIs intended by the writer may differ across writers.]
>> 
>>> 
>>> The avoidance of the formal "interpretation" language in this
>>> informal, descriptive, account is deliberate,
>> 
>> That's a big mistake

I disagree. And without wanting to seem to be pulling rank, I do speak from about 30 years experience of teaching logic to undergraduates. 

>> , because the notion of interpretation is so central to the formal semantics.  Readers cannot possibly understand the semantics without understanding the notion of an interpretation.
>> 
>>> 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.
>> 
>> That's a reasonable way of describing an interpretation.  But point 2 is talking about something different: "2. there is some way to interpret all the blank nodes in the graph as referring to things".  Mappings from blank nodes to things are *not* called interpretations in the formal semantics, they are merely called mappings.

Correct, but this kind of technical distinction is exactly what this sketch-gloss tries to avoid. Readers will surely know that in order to properly understand the semantics they must read more than a short non-normative section with the heading "intuitive summary".

>>  So I do not see how point 4 can possibly be talking about the same notion of interpretation as point 2 and *also* be talking about the formal semantics' notion of interpretation.  So I am still confused about what notion of "interpretations" is intended in point 4, which says: "4. and under these interpretations, each triple S P O in the graph asserts that the thing referred to as S, and the thing referred to as O, do in fact stand in the relationship referred to by P."
>> 
>> How about the following wording instead:
>> [[
>> An RDF graph is true under a given interpretation exactly when:
>> 
>> 1. the IRIs and literals in subject or object position in the graph all refer to things,
>> 
>> 2. there is some way to map all the blank nodes in the graph to things,
>> 
>> 3. the IRIs in property position refer to binary relationships, and
>> 
>> 4. each triple S P O in the graph asserts that the thing referred to as S, and the thing referred to as O, do in fact stand in the relationship referred to by P.
>> ]]

This wording is puzzling as the conditions 1-4 make no reference to the "given interpretation" mentioned in the first sentence. It seems to provide no intuitive or expository advantage by mentioning this, therefore. 

>> 
>>> 
>>> Your suggested re-wording would re-introduce the mathematical
>>> terminology into the intuitive summary, defeating its purpose.
>> 
>> But this document is about the formal semantics, and the notion of an interpretation is absolutely central to understanding the formal semantics.
>> 
>>> 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.
>> 
>> Quite true.
>> 
>>> 
>>> For these reasons, we have decided not to change the wording of
>>> section 5.2 in the way you suggest.
>>> 
>>> Please reply to public-rdf-comments@w3.org indicating whether this
>>> reply is an adequate response to your comment.
>> 
>> No, this is not acceptable.  I'm sure the first wording that I suggested could be improved, but interpretations are absolutely central to the formal semantics and need to be included in the intuitive introduction.  Please consider the revised wording suggested above, or some other wording that properly scopes this introduction.

It is not an introduction. 

>> 
>> Thanks,
>> David
>> 
>>> 
>>> 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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>>> 
>> 
> 
> 
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40 South Alcaniz St.            (850)202 4416   office
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Received on Friday, 4 October 2013 16:32:18 UTC

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