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

From: Guus Schreiber <guus.schreiber@vu.nl>
Date: Wed, 19 Feb 2014 13:37:28 +0100
Message-ID: <5304A588.1030109@vu.nl>
To: Sandro Hawke <sandro@w3.org>, <public-rdf-wg@w3.org>, "Public RDF comments list" <public-rdf-comments@w3.org>

Two follow-up responses inline. I hope all you comments are now addressed.

On 03-02-14 23:58, Guus Schreiber wrote:
> Sandro, (cc: +public-rdf-comments@w3.org)
> Thanks for your comments. Responses inline.
> On 31-01-14 21:32, Sandro Hawke wrote:
>> 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."
> I removed this sentence. It was not required anyway, as we point at the
> end of the intro to the normative docs.
>> 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.
> Put an issue in the ED. Would like to discuss this a bit more with Yves,
> as we don't want to many diagrams. Will come back on this.

The ED is still in progress, but but such a figure is now in there (Fig. 

>> 3.  Typo in 5.1, "habe"
> Corrected.
>> 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.
> Agreed. Still have to work out the details with Yves. I put an issue in
> the ED as a reminder.

There is now a separate subsection on N-Triples, before Turtle is 
introduced. See Sec. 5.1.1 in the ED.


>> 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.
> Changed as suggested.
>> 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
>> <https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-primer/index.html#bib-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.
> Well, this text is a big improvement. I included it in the ED (just left
> out the very last sentence, which I think is not needed).
> Thanks again!
> Guus
> [1] https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-primer/index.html#
>> With these changes, the document will be perfect.    :-)     Keep up the
>> good work.
>>        -- Sandro
Received on Wednesday, 19 February 2014 12:38:00 UTC

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