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Re: My review of RDFa Core 1.1 (2011-12-15 version)

From: Shane McCarron <shane@aptest.com>
Date: Wed, 25 Jan 2012 22:33:24 -0600
Message-ID: <4F20D794.2010907@aptest.com>
To: Niklas Lindström <lindstream@gmail.com>
CC: public-rdfa-wg@w3.org
Thanks for your reply.  In a sane world I would try to get your comments 
integrated tonight.  And that might happen.

On 1/25/2012 8:08 PM, Niklas Lindström wrote:
> Hello Shane,
> On Wed, Jan 25, 2012 at 12:04 AM, Shane McCarron<shane@aptest.com>  wrote:
>> My comments are in line.  I have mostly integrated your changes as you
>> requested.  Note that there are questions in here for Nicklas, Manu, and
>> Ivan.  Please look carefully and answer the questions directed at you.
> That's really great!
> Relevant parts kept and commented inline below. There are some points
> which need further consideration, and it would be good to have input
> from more WG members on those.
>>> "2.2 Examples"
>>> --------------
>>> * The first example uses the terms "author", "prev" and "next". But
>>> these aren't mapped to property IRIs anymore, right? If they don't I
>>> believe it's a poor example. Although I'm a bit confused by the
>>> XHTML+RDFa 1.1 spec which still links to
>>> <http://www.w3.org/2011/rdfa-context/xhtml-rdfa-1.1>, defining
>>> these... In any case, it is probably confusing to have this in RDFa
>>> Core 1.1 if it relies on terms defined for XHTML only...
>> These examples are all properly in XHTML+RDFa and I am loathe to change them
>> at this time.  The terms are defined for XHTML+RDFa and that is the only
>> language we have any control over.  In particular when talking about terms
>> we want to have some concrete examples, and the base only defines 3.
> Ok. Then the initial paragraph here should say "In XHTML 1.1", since
> these terms aren't available in HTML5 (nor XHTML5), right?
>>> * I find the example a bit awkward since it builds up an event by
>>> first implying that the current document is the event, before
>>> enclosing it as a bnode of type cal:Vevent..
>> I removed this example in favor of using something about books to show
>> typeof as per a suggestion from Manu
> Good. But there are still two examples above that using cal:summary
> and cal:dtstart properties which describe the current document
> (compare to the full event described in section 8). Perhaps using
> something like:
>      <body>
>        <h1 property="dc:title">My home-page</h1>
>        <p>Last modified:<span property="cal:dtstart"
>                content="2015-09-16T16:00:00-05:00"
>                datatype="xsd:dateTime">today</span>.</p>
>      </body>
> is better?
>>> * Is it wise to use urn:ISBN URIs for the bibo:Book examples? I'd
>>> rather see even example.org IRIs, or ideally stable real world IRIs
>>> from some linked data library service..
>> We want to show that these sorts of references are legitimate.
> Ok.
>>> "3.4 Plain literals"
>>> --------------------
>>> * As I already brought up, the description of literals in section "3.4
>>> Plain literals" isn't entirely correct. It might be good to add an
>>> example of a literal with language related to the ongoing example
>>> here, such as:
>>>      <http://dbpedia.org/resource/German_Empire>
>>>          rdfs:label "German Empire"@en;
>>>          rdfs:label "Deutsches Kaiserreich"@de .
>> I wasn't smart enough to do this in the time I had.  If you want to provide
>> specific text I am happy to stick it in.  It is an editorial change and we
>> can do it at any time.
> How about this for "3.4 Plain literals": [[[
> Although IRI resources are always used for subjects and predicates,
> the object part of a triple can be either an IRI or a literal. In the
> example triples, Einstein's name is represented by a plain literal,
> specifically a basic string with no type or language information:
>      <http://dbpedia.org/resource/Albert_Einstein>
>        <http://xmlns.com/foaf/0.1/name>  "Albert Einstein" .
> A plain literal can also be given a language tag, to capture plain
> text in a natural language. For example, Einstein's birthplace has
> different names in english and german:
>       <http://dbpedia.org/resource/German_Empire>
>            rdfs:label "German Empire"@en;
>           rdfs:label "Deutsches Kaiserreich"@de .
> ]]]
>>> "3.6 Turtle"
>>> ------------
>>> * Perhaps the first two examples should include the full data being
>>> discussed for the sake of completeness?
>> I couldn't decide what was missing.
> The full data (including the suggested language literals above) seems to be: [[[
> @prefix rdfs:<http://www.w3.org/2000/01/rdf-schema#>  .
> @prefix dbp:<http://dbpedia.org/property/>  .
> @prefix foaf:<http://xmlns.com/foaf/0.1/>  .
> <http://dbpedia.org/resource/Albert_Einstein>
>    foaf:name "Albert Einstein";
>    dbp:birthPlace<http://dbpedia.org/resource/German_Empire>;
>    dbp:dateOfBirth "1879-03-14"^^<http://www.w3.org/2001/XMLSchema#date>;
>    foaf:depiction<http://en.wikipedia.org/wiki/Image:Albert_Einstein_Head.jpg>  .
> <http://dbpedia.org/resource/German_Empire>
>    rdfs:label "German Empire"@en;
>    rdfs:label "Deutsches Kaiserreich"@de .
> ]]]
> The second example could probably do with just the data needed to
> illustrate abbreviation of the subject and datatype, i.e.: [[[
> @prefix dbp:<http://dbpedia.org/property/>  .
> @prefix dbr:<http://dbpedia.org/resource/>  .
> @prefix xsd:<http://www.w3.org/2001/XMLSchema#>  .
> dbr:Albert_Einstein dbp:dateOfBirth "1879-03-14"^^xsd:date .
> ]]]
>>> "6. CURIE Syntax Definition"
>>> ----------------------------
>>> * The following is stated:
>>> [[[
>>> A CURIE is comprised of two components, a prefix and a reference. The
>>> prefix is separated from the reference by a colon (:). In general use
>>> it is possible to omit the prefix, and so create a CURIE that makes
>>> use of the 'default prefix' mapping; in RDFa the 'default prefix'
>>> mapping is http://www.w3.org/1999/xhtml/vocab#. It's also possible to
>>> omit both the prefix and the colon, and so create a CURIE that
>>> contains just a reference which makes use of the 'no prefix' mapping.
>>> This specification does not define a 'no prefix' mapping. RDFa Host
>>> Languages must not define a 'no prefix' mapping.
>>> ]]]
>>> I find this confusing on three accounts:
>>> - Is the default prefix mapping set? Shouldn't it be possible to set
>>> it to what ever the default *vocabulary* is? So that someone can use
>>> e.g.:
>>>      <a vocab="http://example.org/vocab#" rel=":describedby" href="">
>>> To mean:
>>>      <>    <http://example.org/vocab#describedby>    <>    .
>> No.  In CURIEs :foo ALWAYS references the XHTML vocabulary.  We provide no
>> way  to override this.
> I see. So this means that there is no way to use create such a triple
> using @vocab (due to 'describedby' being a predefined term)? I.e. for
> that, one have to use CURIEs with non-empty prefixes or full IRIs?
>>> - This definition of CURIEs state that terms are also CURIEs, does it not?
>> No.  TERMS are things that are looked for BEFORE CURIEs are matched.
> Ok. The interplay of concepts is quite intricate here. It seems to me
> to be an overlap between terms and CURIEs with no prefix and leading
> ":"? I had the idea that terms were distinct from CURIEs in that the
> latter always started with a (possibly empty) prefix and ":". This
> since some terms are predefined and some resolved against the local
> default vocab (as defined in section "7.4.3 General Use of Terms in
> Attributes"). But not all references are terms, that seems clear.
> So it seems that certain expressions like "item@a" or "value#b" would
> fail to match the rules for terms, but are valid CURIEs. How would
> they then be resolved? From the next piece I conclude: not at all.
>>> - Although I interpret "RDFa Host Languages must not define a 'no
>>> prefix' mapping" to mean TODO
>> Not sure where you were going with this, but...
> (Ugh; apparently I left this incomplete. I'm so sorry.) Well, at the
> time I thought that host languages could, in their default context,
> define such a mapping with the default vocabulary mechanism. But that
> is only for terms, and not for this 'no prefix' mapping; right? (And
> as said above, I conclude that those two expressions ("item@a" and
> "value#b") would not resolve.)
> Am I reading this right?
>>> * I would like to see a note here about CURIEs effectively working
>>> like protocol shorthands, with appropriate warnings about how they
>>> *may* overshadow existing or future protocols (especially profiles
>>> with many prefixes could cause this in a non-obvious way). This is
>>> what we discussed when we resolved ISSUE-90 [1]. Note though that the
>>> resolution of ISSUE-125 [2] might remove the need for this.
>> Added some text
> Great, this was definitely needed. However, I'm not satisfied with it yet.
>   - In "it is possible though unlikely, that schemes will be introduced
> in the future that will conflict with prefix mappings defined in a
> document", can we really say "unlikely"? The creation of schemes is
> entirely independent of the use of prefixes in RDF contexts, so we
> really don't know. We've already seen e.g. "http", "geo", "tag" and
> "urn", all in<http://prefix.cc/>. Perhaps if we say: "it is possible
> though unlikely, that popular schemes will be introduced in the
> foreseeable future that will conflict with (popular) prefix mappings".
> All of this requires monitoring and interception by people aware of
> both contexts. This note is where we raise awareness of this need for
> coordination. Of course problems won't appear over night, maybe not
> for many years; hopefully never. (And I do hope that the creation of
> new IRI schemes will continue to decrease in popularity). I gather
> that our position is to expect people to understand this and inform
> each other early on. (I'm just not sure.)
>   - The example uses an @href, but those cannot contain CURIEs, so they
> are safe. The attributes of concern are @about and @resource. (Of
> course if the use of CURIEs would catch on and become available to
> "actionable" link attributes the situation is worsened.)
>   - "In neither case would this RDFa overshadowing of the underlying
> scheme alter the way other consumers of the IRI treat that IRI." I
> don't follow. Do you mean in the sense of consumers *not* using RDFa,
> only the lexical value? That seems irrelevant to me for our purposes.
>   - "It could, however, mean that the document author's intended use of
> the CURIE is misinterpreted by another consumer as an IRI." That
> should probably be: "It does mean that the document author's intended
> use of an IRI is misinterpreted, since any RDFa consumer would expand
> that as a CURIE and get a different IRI as a result."
> Note that in attributes where a prefix overshadows a scheme the
> resulting IRI in the RDF data is irrevocably different from its
> "CURIE-looking-like an-IRI" origin. And a consumer of the resulting
> RDF may never detect this. It's even more untraceable if the triples
> are transmitted further.
>   - "The working group considers this risk to be minimal at worst." I'd
> strike "at worst". (The notion "CURIE injection" comes to mind in a
> scenario where some social networking giant starts to publish snippets
> of RDFa for unassuming web administrators to use, poised against
> another proprietary protocol of some major digital artifact vendor,
> where the scheme and prefix happen to be the same. Of course I'm
> really exaggerating here. But perhaps you see my point.)
> (And while I fear there's little support for disallowing
> "prefix://"-like forms from being CURIEs, *if* that would be accepted
> then we should of course reformulate this note to highlight the
> lessened risk, and explain which kinds of schemes (forms of IRIs) are
> still at risk and require this care.)
>>> "7.2 Evaluation Context"
>>> ------------------------
>>> * Should it be explained that "parent subject" is only used, as far as
>>> I can see, for handling incomplete triples? (Or am I missing
>>> something?)
>> They are, but I felt it was clear enough from the language.
> Ok.
>>> * Perhaps the concept "parent object" could be renamed to "parent
>>> resource", due to the way it is used in the processing.
>> I felt it was too late to change this.
> Ok.
>>> "7.4.2 General Use of CURIEs in Attributes"
>>> -------------------------------------------
>>> * The note states: "An empty attribute value (e.g., typeof='') is
>>> still a CURIE, and is processed as such.". Is that really true? Isn't
>>> it rather so that certain attributes have meaning (effect on the
>>> processing) even when empty? The notion of an empty CURIE strikes me
>>> as strange.
>> I was not sure how to change this.  While it is odd, it is important for
>> many steps in the sequence that empty attributes are not ignored.
> Many RDFa attributes expresses meaning even when empty, so their
> presence is in itself important information.
>>> * The last sentence "As a special case, _: is also a valid reference
>>> for one specific bnode." is the only explanation of what "_:" means. I
>>> think it should be elaborated a little upon, making it clear how it
>>> works and why. (Also I was under the impression that it should
>>> generate a unique bnode each time it is used (and not represent the
>>> same bnode across the document), but that does not seem to be the
>>> case?)
>> I have no idea at all what to do here.
> Nor do I. I've never used it, I think usage of empty @typeof fulfills
> my potential needs for what I thought it meant, and I don't really get
> why a kind of bnode "singleton" would be useful at all. Can anybody
> explain what it means and is used for?
>>> "7.5 Sequence"
>>> --------------
>>> * Step 1 (and 3). Shouldn't the local list of IRI mappings actually be
>>> set to *a copy of* the list of IRI mappings from the evaluation
>>> context? In step 3, this local list is mutated by adding to it, so we
>>> must ensure that someone implementing it like this doesn't affect the
>>> list for following sibling elements. Either that or express "adding to
>>> the local list" differently, in functional terms.
>> This is not really an issue.  'local' is local to each iteration of the
>> depth-first processing loop.  Nothing is passed 'by reference' in this
>> algorithm.
> Ok.. I see what you mean. Still, since it reads "the local list of IRI
> mappings is set to the list of IRI mappings from the evaluation
> context", and then "and these are added to the local list of IRI
> mappings", might one not get that impression? It concerned me since in
> step 13, the new evaluation context is either "a copy of the current
> context that was passed in to this level", or it is constructed again.
> Well, I may be splitting technical hairs here, and I suppose
> implementers won't actually be misled into mutating a shared list for
> all levels. And if they still do, basic testing will quickly show them
> the error in that. :)
>>> * Step 9. Shouldn't there be an error or warning if both @rev and
>>> @inlist are present?
>> No - @rev is not relevant to @inlist, but an @rev on the element might still
>> generate triples relevant to the subject (think of @rev, @rel and @inlist on
>> the same element).
> Ah, of course; very good point! Thanks.
>>> * Step 10. It would be good to explain why "Also, current object
>>> resource should be set to a newly created bnode".
>> Fixed
> Hm...  It now says: "Also, current object resource should be set to a
> newly created bnode (so that the incomplete triples have a subject to
> connect to if they are ultimately turned into triples)".
> But I thought that the subject for the incomplete triples is to be the
> *parent subject* resource (and the very reason for it to exist). Note
> that this newly created bnode in step 13 is used for the next parent
> *object*. All of this to support:
>      <div about="#parent_subject" rel="dc:hasPart">
>          <p property="rdfs:label">anonymous object</p>
>      </div>
> To generate:
>      <#parent_subject>  dc:hasPart [ rdfs:label "anonymous object" ] .
> In the more common(?) cases of hanging rels, where nested markup
> defines a new resource with @about, @typeof or a resource atttribute,
> this newly created bnode will be replaced and forgotten by that/those.
> It's late though so I need someone to verify this! If I'm not totally
> lost, the explanation for the newly created bnode should probably say
> something like: "so that the incomplete triples have an object to
> connect to if the first triple generating item encountered in a
> subsequent level is a predicate". (Well, some legible wording of
> that..)
>>> "7.6 Processor Status"
>>> ----------------------
>>> * While this section is good, and the concept of a processor graph in
>>> general can be useful, I do wonder if it's really tangential to
>>> defining the core of RDFa processing? Have we considered placing it in
>>> a separate document? If I understand correctly, it came to life as a
>>> part of the now removed custom profile processing mechanics? Mostly
>>> thinking out loud here though.
>> It is needed for warnings still.
> Ah, yes, of course.
>>> * Section "10. RDFa Vocabulary Expansion" should include the relevant
>>> triple from the cc vocabulary used for expansion?
>> I think it does.    It shows the dc: reference that the cc: item refers to.
> True, but I meant the triple causing this to expand. That is, in the
> RDFa (nice!) from<http://creativecommons.org/ns#>, this triple:
>     cc:license rdfs:subPropertyOf dct:license .
> is specifically what makes the expansion infer dc:license from cc:license.
>>> "B.4 Changes"
>>> -------------
>>> Could this perhaps be merged with its only subsection "B.4.1 Major
>>> differences with RDFa Syntax 1.0"?
>> Hmm - maybe.  Not right now though.   Thinking about it.
> Ok. Perhaps it'd be more valuable to have more than one subsection,
> e.g. "Minor differences", "Complying to RDFa 1.0" or similar (though
> that latter part in isolation is odd since it advices usage of
> deprecated features like @xmlns).
> That should be all.
> Thanks for addressing my entire bulk of remarks! Impressive editorial
> work (which I've gathered is your modus operandi).
> Best regards,
> Niklas

Shane McCarron
Managing Director, Applied Testing and Technology, Inc.
+1 763 786 8160 x120
Received on Thursday, 26 January 2012 04:34:15 UTC

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