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Re: A few comments on Primer (esp re Semantics)

From: Arnaud Le Hors <lehors@us.ibm.com>
Date: Mon, 3 Feb 2014 06:42:53 -0800
To: Sandro Hawke <sandro@w3.org>
Cc: public-rdf-wg@w3.org
Message-ID: <OFB2E8B20C.1252C505-ON88257C74.0050C086-88257C74.0050D59C@us.ibm.com>
I love your proposed text! Well done.
--
Arnaud  Le Hors - Software Standards Architect - IBM Software Group


Sandro Hawke <sandro@w3.org> wrote on 01/31/2014 12:32:25 PM:

> From: Sandro Hawke <sandro@w3.org>
> To: public-rdf-wg@w3.org, 
> Cc: RDF WG <public-rdf-wg@w3.org>
> Date: 01/31/2014 12:32 PM
> Subject: A few comments on Primer (esp re Semantics)
> 
> I recently had a chance to read through the Primer, and mostly it's 
> great but there were a few things that bugged me.    Hopefully 
> they're not to hard to fix.
> 
> 1.   The use of the word "informative" in the first paragraph is a 
> problem.   I don't think most people have any idea that in 
> standards-speak "informative" has a different meaning than in normal
> English.  So to most people, that bit will just sound kind of 
> dumb.   (I think it's a bad idea to ever use that word when we have 
> a perfectly good alternative in "non-normative", but it's 
> particularly problematic in the beginning of a primer.
> 
> I was thinking something like, "This document is a companion to a 
> set of W3C standard, which are listed at the end of this 
> introduction.  This document itself is not a standard, though."
> 
> 2.  With my naive reader hat on, I was still feeling pretty confused
> at the end of 3.5, badly wanting a diagram.   Maybe move the one 
> from later up to this point?   Not a show-stopper.
> 
> 3.  Typo in 5.1, "habe"
> 
> 4.  In 5.2 I think it's important to introduce N-Triples with saying
> it's a subset of Turtle.   That's the most important thing about it.
> 
> 5.  In 5.2 I think we have a chance to push back against the biggest
> problem in RDF deployment.    Under RDF/XML I suggest:
> 
>  delete:  RDF/XML was the only normative syntax for RDF when RDF 1.0
> was published in 2004. 
> 
>  add: When RDF was original developed in the late 1990s, this was 
> its only syntax, and some people still call this syntax "RDF". In 
> 2001, a precursor to Turtle called "N3" was proposed, and gradually 
> the other syntaxes listed here have been adopted and standardized.
> 
> The main point is that for many years, all the way back to 1997 (I 
> think, 1999 at least), it wasn't so much the "only normative 
> syntax", it was the ONLY syntax.    .rdf files are RDF/XML.   
> Professionals in this field still call RDF/XML "RDF".    We need to 
> help newcomers understand this happens and what it means when it does.
> 
> 6.  This is the hard one.   I was eagerly reading the document up to
> section 6. Semantics, just thinking like a programmer, and nodding 
> in agreement as everything up to this point made perfect sense.    
> Then I got hit with this stuff about "formal model-theoretic 
> semantics" and "truth-preserving conditions", and it suddenly just 
> seemed like handwaving and obscure "semantics" stuff I'd never care 
about.
> 
> I think this is a great place to explain to the RDF community WHY 
> there are formal semantics and who might want to read rdf11-mt.   As
> the text is now I'm afraid it just feeds the feeling that rdf-mt is 
> gobbledegook no one needs to pay attention to, unless they're 
> working on a PhD.
> 
> Here's a strawman to show the kind of text I think we need:
> An overarching goal in the use of RDF is to be able to automatically
> merge useful information from multiple sources to form a larger 
> collection that is still coherent and useful.   As a starting point 
> for this merging, all the information is conveyed in the same simple
> style, subject-predicate-object triples, as described above.    To 
> keep the information coherent, however, we need more than just a 
> standard syntax; we also need agreement about the semantics of these 
triples.
> 
> By this point in the Primer, the reader is likely to have an 
> intuitive grasp of the semantics of RDF.  (1) The IRIs used to name 
> the subject, predicate, and object are "global" in scope, naming the
> same thing each time they are used.  (2) Each triple is "true" 
> exactly when the predicate relation actually exists between the 
> subject and the predicate.  (3)  An RDF graph is "true" exactly when
> all the triples in it are "true".    These notions, and others, are 
> specified with mathematical precision in the RDF Semantics document 
[RDF11-MT
> ].
> 
> One of the benefits of RDF having these declarative semantics is 
> that systems can make logical inferences.  That is, given a certain 
> set of input triples which they accept as true, systems can in some 
> circumstances deduce that other triples must, logically, also be 
> true. We say the first set of triples "entails" the additional 
> triples. These systems, called Reasoners, can also sometimes deduce 
> that the given input triples contradict each other.  
> 
> Given the flexibility of RDF, where new vocabularies can be created 
> when people want to use new concepts, there are many different kinds
> of reasoning one might want to do.  When a specific kind of 
> reasoning seems to be useful in many different applications, it can 
> be documented as an "entailment regimes".   Several entailment 
> regimes are specified in RDF Semantics.     For technical 
> description of some other entailment regimes and how to use them 
> with SPARQL, see SPARQL 1.1 Entailment Regimes http://www.w3.org/TR/
> sparql11-entailment/ .   Note that some entailment regimes are 
> fairly easy to implement and reasoning can be done quickly, while 
> others require a very sophistical techniques to implement 
> efficiently.  Some entailment regimes have been proven to be 
> intractable, but they might still be useful for small data sets.
> 
> ... then go into the rdfs:domain example ...

> I'm not attached to any of that wording -- I hope someone else can 
> do better -- but hopefully you see how I'm trying to convey things 
> people really need to know to operate in the RDF space without 
> making a lot of assumptions about what they already know.   I think 
> we have to do something like that.
> 
> With these changes, the document will be perfect.    :-)     Keep up
> the good work.
> 
>       -- Sandro
Received on Monday, 3 February 2014 14:44:06 UTC

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