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Re: RDF Semantics - Intuitive summary needs to be scoped to interpretations (ISSUE-149)

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 10 Oct 2013 01:05:54 -0500
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, www-archive <www-archive@w3.org>, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>, Ivan Herman <ivan@w3.org>, Sandro Hawke <sandro@w3.org>
Message-Id: <AF04C492-0DDB-454F-8028-EE73CE931C2B@ihmc.us>
To: David Booth <david@dbooth.org>
Hi David

This is NOT an official WG response, but only an informal note to explain some of the background thinking and discussions behind some of the decisions we took. Please don't copy this to the public comments list. I added Sandro to the CC list as he seems interested in this stuff. 

The 2004 semantics document tried to do (at least) two things at once. It is a formal, normative description of the semantics, but it also tried to be a "tutorial" in various places, including in the section you refer to and the extended glossary. This introductory material has gotten some good reviews (thanks) but also has gotten some criticism, especially with regard to its appropriateness for inclusion in a normative standard document. And for sure, it made the document a lot longer than it would have been without it, and the sheer length of the RDF specs has come in for a lot of criticism. And for some readers, it is an irritating distraction. 

Early in this WG, after some extended discussions, we decided that the public interest would be better served by separating the explanatory/tutorial/introductory material from the formal technical normative material, and moving the former to a different document, a kind of introduction/tutorial/primer document that is yet to be written, and thereby making the normative technical document shorter and crisper. This sacrifices readability for precision and exactness, but there was a consensus in the WG that at this time in the evolution of RDF, precision and exactness (and comparative brevity) were more important than introductory exposition, in the actual normative specification.  This is why the material that you now miss, is missing. (You may also notice that the RDF1.1 Concepts document is also much shorter and brisker than the 2004 version, for the same reasons.) As I say, the plan was (and still is) to move this all to a 'primer' document rather than abandon it entirely, but this is why its not in the actual semantics document. 

The short "intuitive summary" section on which you commented earlier represented an editorial lapse on my part when drafting the new document, where my old teaching instincts overwhelmed my responsibility as WG editor. Your comment made me realize the error of my ways. 


On Oct 9, 2013, at 10:16 PM, David Booth wrote:

> Hi Pat (and others),
> I would not raise an objection to deleting the Intuitive Summary, but I think there would be a loss to the public in deleting it.  I also really liked the explanation of interpretations that you included in the 2004 version, and miss it in the current draft.  It really gave very good insight into the concept.  So personally, I think a better solution would be to add back your explanation of interpretations and tweak the Intuitive Summary section as needed.
> You mentioned this concern:
> [[
> Consider:
> "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,
> But suppose that they refer to things that are not in the universe of the given interpretation, then this is false.
> ]]
> But AFAICT that is impossible, because "refer" is defined in sec. 4 to be relative to an interpretation:

In the above sentence, I was using the word "refer" in its normal English usage, informally. But in any case, the point still stands: they might be referring to things in the universe of a different interpretation. 

> http://www.w3.org/TR/2013/WD-rdf11-mt-20130723/#notation
> [[
> The words denotes and refers to are used interchangeably as synonyms for the relationship between an IRI or literal and what it refers to
> **in a given interpretation** . . . .
> ]]
> (my emphasis).   And the wording that I suggested makes clear what interpretation is intended

I don't accept that it does make this clear. 

> , so the IRIs and literals *cannot* refer to things outside of that interpretation's universe.
> Also, I don't know what you mean when you wrote:
> [[
> No doubt David would respond, but readers should be *obliged* to think about interpretations, and then my reply would be, OK, but if so then this section is inappropriate in the first place, so let us delete this section.
> ]]
> Why would that section be inappropriate if readers are obliged to think about interpretations?  It seems to me to give a fairly concise summary of the formal approach taken.
> Finally, at the risk of restating the potentially obvious, I do not see how anyone could possibly understand the formal semantics without understanding the idea of interpretations, since they are so central to the semantics.

The notions of reference (what a name refers to, or denotes) and truth are pre-theoretic. They are part of our ordinary understanding of the world. Interpretations simply formalize (if one can call such a simple construct a 'formalization") this intuition so that one can do some mathematics with it. The idea of this section was to use the ordinary English words "refer" and "interpret" to re-state the truth conditions, just to show how mind-numbingly obvious they are, and hopefully to indicate how the formal machinery corresponds closely to the pre-theoretic ideas. However, this purpose is undermined if this section is understood formally rather than intuitively. 

But, as I say, I now think that this idea, of trying to connect the formal notions to an intuition, was probably a mistake in this document and went against the spirit of a WG decision. 


<<Other in-line responses, below, are part of our continuing, um, debate, and are aside from discussions of the RDF documents.>>

> > On Oct 4, 2013, at 10:51 AM, Peter Patel-Schneider wrote:
> >
> > > In my opinion the divergence boils down to Pat believing that this informative section should be more informal and David believing that it has to be more formal.
> I don't exactly think it has to be more formal, but just that: (a) it needs to mention interpretations, because that concept is so central to the formal semantics; and (b) the statement about the conditions under which a graph is true *needs* to be scoped to an interpretation to make any sense at all.

That is exactly what it should *not* be, in order to convey the point it was intended to be conveying. 

>  If one talks about a graph being true, without mentioning an interpretation, IMO the most sensible way to understand such a statement is to take it as meaning that the graph is *satisfiable*

No, that is not the right way to understand it. Truth and satisfiability are not the same thing at all. (That pigs can fly, is satisfiable.) To say that a graph (or any other assertion or sentence) is true, is to say that when it is interpreted *in the actual world*, its truth-value is true. That is the pre-theoretic, intuitive, notion. Someone says something, you figure out *what* they are saying, and you judge whether it - what they are saying - is true. Nothing in that account mentions interpretations. It does mention, implicitly, the truth conditions (section 5) and we could say that it *presumes* an interpretation that the speaker and hearer have in common. And that is where the naivitée of this naive account is displayed, of course, that implicit assumption of a common interpretation; because when we have the kind of distancing between publisher and reader that is inevitable on the semantic web, and communicate using IRIs which have no assumed common background of linguistic meaning, we cannot presume this common shared interpretation, this "common ground" (http://semantics.uchicago.edu/kennedy/classes/f07/pragmatics/stalnaker02.pdf, or http://plato.stanford.edu/entries/discourse-representation-theory/.)  So this is where the interpretation idea comes in, because we have to, as it were, survey the possible things you might mean when you publish some RDF. We don't know what world you are talking in, so we have to consider all *possible* worlds. Which is what interpretations are (the thin, pale shadows of formalizations of).

Long - very long - story short, the analysis of real linguistic communication - including Web communication - between cognitive agents (people, mostly) involves model-theoretic ideas, but it also involves a *lot* more. RDF, indeed the entire semantic web, is a tiny part of this larger picture, and can be fitted into it in one small corner. But in order to be useful, it does need to be fitted into it accurately. 

> : that there *exists* an interpretation under which the graph is true, and hence we can take the graph as being true. (Conversely, if the graph is not satisfiable then we cannot take it as being true.)  OTOH, such a statement could be taken to mean that the graph is true **in some unspecified interpretation**

The one that is presumed when we talk (pre-theoretically) about what people are referring to when they say "Everest" (for example), and when we make judgements of the truth or otherwise of their utterances in the actual, real, world we are all talking about. Yes, exactly. 

> .  But that would be a very bad way to write

Try telling that to linguists. Or to literary theorists, or historians, or philosophers of language, or indeed pretty much anyone who uses language professionally. Not only is this not a bad way to write, its the ONLY way to write if we are trying to anchor model theory in an intuitive description of how communication actually happens. Except, calling the actual world "unspecified" seems a little strange. 

> , because the interpretation under which the graph is true would be an implicit unbound variable, which as we all know is a big no-no.  

It is implicit, yes, but I don't know what kind of assumptions you are appealing to by calling this a big no-no. Contexts are usually implicit, right?

> Instead, the problem can be easily solved by adding "under a given interpretation" to the sentence.  (Of course, the notion of an interpretation should first be explained.  But that is a different omission that should be addressed anyway.)
> And regarding this:
> http://lists.w3.org/Archives/Public/public-rdf-wg/2013Oct/0079.html
> [[
> 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.
> ]]
> (Wow, you're calling *me* condescending, after repeatedly telling me to "go read a book"???)  That's both: (a) quite a projection; and (b) *really* unfair and unhelpful.  Fortunately I'm thick skinned and I have a good sense of humor.  :)

Well, you weren't meant to read that, obviously. But my dear fellow, *have* you read the books, in fact? Is it really condescending for me to suggest that you might want to read up something a little more extensive than a few paragraphs that I wrote about RDF, before claiming that you have discovered a new way to understand model theory, or setting out to correct my misunderstanding of it, or telling me that my perspective is too limited? I don't mean to pull rank on you here, but I have been studying this stuff now, as well as teaching it, for about 40 years. For a few years, I invented new model theories for a living. God knows there are a lot of things I don't fully understand, but model-theoretic semantics is one topic I really do have pretty thoroughly grokked. 

> Thanks,
> David
> -------- Original Message --------
> Subject: Re: RDF Semantics - Intuitive summary needs to be scoped to interpretations (ISSUE-149)
> Date: Wed, 09 Oct 2013 15:06:19 -0700
> From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
> To: David Booth <david@dbooth.org>
> CC: public-rdf-comments <public-rdf-comments@w3.org>
> Greetings David:
> This is an official RDF working group response to your message
> http://lists.w3.org/Archives/Public/public-rdf-comments/2013Oct/0010.html
> on Section 5.2, Intuitive Summary, of the RDF 1.1 Semantics document.
> The Working Group thanks you for your concerns on this aspect of the RDF
> recommendations, which have been tracked as ISSUE-149.
> Section 5.2 is an informative section and was only put in as an short,
> easier-to-understand gloss of some of the the preceeding more-formal
> section.  Both your comment and the ensuing discussion have made it clear
> that the section is not achieving its purpose.  As there appears to be no
> consensus on what changes, if any, should be made to the section, it is the
> intent of the working group to just remove the entire section.
> Could you please respond to public-rdf-comments@w3.org as to whether
> removing this non-normative, non-formal section would satisfactorily address
> your concern?  If you are satisfied, then the section will be removed from
> the document.
> Peter F. Patel-Schneider
> for the W3C RDF WG
> On 10/01/2013 10:15 PM, 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, 10 October 2013 06:06:26 UTC

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