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Re: RDF Semantics Editors Draft?

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 14 May 2012 00:56:20 -0500
Cc: David Wood <david@3roundstones.com>, Peter F. Patel-Schneider <pfpschneider@gmail.com>, public-rdf-wg WG <public-rdf-wg@w3.org>
Message-Id: <13C9D8EE-DD56-49C8-92A4-0B9ADF35FE2A@ihmc.us>
To: Richard Cyganiak <richard@cyganiak.de>

On May 13, 2012, at 3:48 PM, Richard Cyganiak wrote:

> Hi Pat,
> 
> On 13 May 2012, at 07:45, Pat Hayes wrote:
>> The problem with making the rules normative is that these rules are NOT in fact a good way to implement a reasoner.
> 
> Red herring. We are not talking about these rules because they may or may not be a good way of implementing a reasoner. We are talking about them because they are easier to understand for most readers. Implementers are free to use whatever approach they like as long as it produces correct results.
> 

Fine, but then these rules are NOT normative. What is normative is correctness, and correctness can only be defined model-theoretically. 

>> I think they should be in a separate doument entirely, perhaps as part of the test cases,
> 
> This would be inappropriate. The test cases are supposed to be machine-processable so that one can have a test harness that automatically verifies an implementation.

I don't see why this would prohibit the rules being there. All a rule is, is a pattern of an entailment. The test cases have entailments in them now. It would be easy to rephrase the rules in a test-case-like format, using tables of patterns. They would be used to test reasoners, which should be able to demonstrate the conclusion when told to assume the antecedents. 

> 
>> and no claims should be made as to their completeness, and no long and extremely opaque (and flawed) completeness proofs should be included, even in an appendix. Nobody gives a damn about completeness in any case.) 
> 
> -1. I do give a damn about the completeness of the rules.

I really do not understand your position. How can you care about completeness when you dont want us to even have the content which allows us to define the very concept of completeness? 

> 
>> I am sympathetic to the idea that RDF should simply not have a formally defined semantics at all. This would solve all of these (and many other) problems at a stroke, and I could get on with other things in my life.
> 
> Pat, what is this. Everyone in this WG volunteers their time, and is free to walk away. So are you. Whether you can go on with other things in your life is entirely orthogonal to the question whether RDF has a formally defined semantics.
> 
>> model-theoretic semantics has been the accepted norm for semantic specifications in linguistics, logic, database theory and the theory of computation now for about 40 years,
> 
> Ridiculous overstatement.

I don't agree, and if you like, we can play a game of citation to see who is right. 

>> If we put a typo into an inference rule, or simply forget some special case, and a later reader notices this and publicises the error (as has indeed happened), then what basis do they have for claiming that the rule is wrong? If the rule itself is normative, then it CANNOT be wrong, even if it sanctions invalid inferences.
> 
> And making the model theory normative instead of the rules saves us from typos in the normative parts how?

The actual statement of the truth conditions can be checked fairly easily. Small errors in rules, and especially missing cases needed for completeness, are MUCH harder to spot. There are errors in the 2004 rules, in fact, which were only discovered months after publication and after the most thorough vetting by some extremely careful people (try reading the email logs shortly before LC to see how anal this got at times). Even the early implementers (Jos deRoo had a rule engine in 2003 which we used often to check completeness) did not notice them. 

>>>> 2) Implementers of various specs (incl. RDF, RDF Schema, SPARQL) read it, in order to understand how their systems should behave, especially with regard to datatypes and RDFS inference.
>> 
>> If they are seeking a guide to how any system should *behave*, then they need to understand that semantics is not about behavior but rather about truth, satisfaction and consistency
> 
> Falsehood.

No, this is EXACTLY true. Semantics does not describe or even mandate ANY behavior. An "engine" which inputs RDF and does exactly nothing to it except print it back out unchanged, is a perfectly correct and conformant RDF engine. Behavior is constrained by semantics but not described by it. 

>>>> 3) Authors of RDF Schema vocabularies read it, in order to understand the consequences of declaring domains, ranges, subproperties and so on.
>>>> 
>>>> 4) RDF newbies read it, because this is where they happened to end up after some googling or link-clicking and they don't understand the big scheme of things yet.
>> 
>> The second paragraph of the document starts "This is one document in a set of six (Primer, Concepts, Syntax, Semantics, Vocabulary, and Test Cases) ..." and they might then hazard a wild guess that the one called "Primer" might possibly be a better place to start. 
> 
> The paragraph you quote is from the “Status of this Document” section, which is the one that everyone who has ever seen a W3C document immediately skips because it's just boilerplate.

Well, in this case, it clearly isnt just boilerplate, because it points you to the primer, which apparently matters. 

>> If they habitually read documents without checking the first page, then I really don't think we have any responsibility for what kind of a mess they get into, frankly.
> 
> Look Pat, no one reads documents front-to-back on the web. People arrive in the middle of the document by following a link, or they scroll around until they see something that looks like a ToC and jump to the section whose title looks most relevant, or they just search within the document for the keyword of their interest.

So, what follows? Do we need to put a warning on every page or at every link anchor, saying "You might want to read the primer first" ? We are supposed to be writing a technical specification, not a Web blog. Surely we can expect a minimal level of literary competence in our readers? 

> 
>> What would it mean to make those rules normative? Would an efficient tableax-based reasoner be then illegal?
> 
> No, why would it?

Because if would not be using rules at all; but the rules are normative. Which I take to mean, if you aren't using the rules, you are are doing it wrong.

>>>> I think we all agree that this is *not* the document you should be looking at in your first encounter with RDF.
>> 
>> If you know nothing about logical methods, inference engines, machine inference? Yes, it might not be a good starting point if you are this ignorant, indeed.
> 
> Inappropriate display of arrogance.

Why? There seems to be a ground assumption here that our typical reader knows absolutely nothing about semantics, logic, reasoners, reasoning, or indeed almost anything about the technical field in which these specifications are situated; and so we have to write our specifications - not a beginners guide, but the actual technical specifications - as though they had the title "RDF for Dummies". (In fact, it now seems that we cannot even assume that our readers are able or willing to read a document from the beginning. I would be interested to know what our 'typical' reader should be presumed to know. Do they understand what a paragraph is? A glossary? An index?) 

This seems to me to be ridiculous. It is not our purpose to write basic introductory courses in words of no more than three syllables for people who know nothing about the topic. Maybe the world needs such documents, but someone other than a WG should be writing them. Our job is to lay out a clear, unambiguous specification of the language(s) which will enable competent professional people to use them correctly. 

>>> This problem could be solved easily with the insertion of some language in the introduction pointing to the Primer in the first paragraph (instead of just the Vocab and Concepts, as it does now).
>> 
>> See above. It refers to the primer in the second paragraph of the document. 
> 
> In the section that nobody reads. The Introduction is silent on the topic of which other documents you should already be familiar with before starting this one.

By all means let us copy paragraph 2 of the Status section into the Introduction, where people might possibly see it.  I presume this editorial decision will apply to all the technical documents. 

Pat

> 
> Best,
> Richard
> 
> 
> 
> 
>> 
>> Pat
>> 
>>>> 
>>>> Best,
>>>> Richard
>>>> 
>>>> 
>>>> 
>>>>> 
>>>>> peter
>>>>> 
>>>>> 
>>>>> On 04/25/2012 11:27 AM, David Wood wrote:
>>>>>> Hi Peter and Pat,
>>>>>> 
>>>>>> The RDF WG briefly discussed the need for an RDF Semantics editors draft at today's telecon.  I am aware that there are a lot of open issues and therefore hard to produce a draft, but perhaps it makes sense to have a single document that lists the issues in one place.
>>>>>> 
>>>>>> In any event, we would like to discuss this at next week's telecon if you can make it.  Thanks.
>>>>>> 
>>>>>> Relevant comments from IRC (no log published yet since the meeting isn't over):
>>>>>> [[
>>>>>> ivan: one thing that came up early was discussion to change title of RDF Semantics document, reorganize to make the rules normative and deemphasize the model-theoretic semantics AlexHall @ 11:20
>>>>>> ... think it's a good thing to do but huge amount of editorial work AlexHall @ 11:20
>>>>>> cygri: is there an editors draft of RDF Semantics yet? 11:21
>>>>>> [no] 11:21
>>>>>> cygri: given that there are larger changes to the doc, would feel better if there were an editors draft by now. 11:21
>>>>>> guus: suggest we should put it on the agenda for next week
>>>>>> ]]
>>>>>> 
>>>>>> Regards,
>>>>>> Dave
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>> 
>>>> 
>>> 
>>> 
>>> 
>> 
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>> 
>> 
>> 
>> 
>> 
>> 
> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Monday, 14 May 2012 05:56:56 GMT

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