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

From: Guus Schreiber <guus.schreiber@vu.nl>
Date: Mon, 3 Feb 2014 23:58:25 +0100
Message-ID: <52F01F11.1040809@vu.nl>
To: Sandro Hawke <sandro@w3.org>, <public-rdf-wg@w3.org>, "Public RDF comments list" <public-rdf-comments@w3.org>
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.

> 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.

> 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 Monday, 3 February 2014 22:58:53 UTC

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