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meeting record: 2009-04-02 RDF-in-XHTML Task Force telecon

From: Ralph R. Swick <swick@w3.org>
Date: Thu, 02 Apr 2009 12:28:10 -0400
Message-Id: <>
To: public-rdf-in-xhtml-tf@w3.org
Cc: public-swd-wg@w3.org
The record of today's RDFa discussion are avaialble as


A text snapshot follows.


                        RDF-in-XHTML Task Force

02 Apr 2009


      [2] http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2009Apr/0018.html

   See also: [3]IRC log, previous [4]2009-03-19

      [3] http://www.w3.org/2009/04/02-rdfa-irc
      [4] http://www.w3.org/2009/03/19-rdfa-minutes.html


          Ralph Swick, Manu Sporny, Shane McCarron, Mark Birbeck

          Ben_Adida, Michael_Hausenblas




     * Topics
         1. Action Review
         2. Report on AC Meeting
         3. @prefix syntax discussion
     * Summary of Action Items

Action Review

   ACTION: [PENDING] Ben to put up information on "how to write RDFa"
   with screencast possibly and instructions on bookmarklet. [recorded
   in [10]http://www.w3.org/2008/11/06-rdfa-minutes.html#action12]

     [10] http://www.w3.org/2008/11/06-rdfa-minutes.html#action12

   ACTION: [PENDING] Jeremy to demonstrate GRDDL with XHTML/RDFa once
   the NS URI is set up. [recorded in

     [11] http://www.w3.org/2008/09/11-rdfa-minutes.html#action03

   ACTION: [DONE] Manu to look at
   ec/0037.html about resolving relative URIs [recorded in

     [12] http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2008Dec/0037.html
     [13] http://www.w3.org/2009/01/08-rdfa-minutes.html#action15

   Manu: I've replied and asked twice for a response
   ... I think they're accepting the response
   ... so I think we can consider this done

   ACTION: [PENDING] Manu to write summary for Semantic Web Use Cases
   for Ivan. [recorded in

     [14] http://www.w3.org/2008/09/11-rdfa-minutes.html#action09

   ACTION: [PENDING] Mark create base wizard suitable for cloning
   [recorded in

     [15] http://www.w3.org/2008/09/11-rdfa-minutes.html#action12

   ACTION: [DONE] Mark to review reasoning on setting explicit about=""
   on HEAD and BODY [recorded in

     [16] http://www.w3.org/2008/12/18-rdfa-irc

   -> [17]The implied @about="": Explanation and some problems Mark

     [17] http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2009Apr/0000.html

   ACTION: [PENDING] Mark to send Ben ubiquity related wizard stuff
   [recorded in

     [18] http://www.w3.org/2008/11/20-rdfa-minutes.html#action11

   ACTION: [PENDING] Mark write foaf examples for wiki [recorded in

     [19] http://www.w3.org/2008/09/11-rdfa-minutes.html#action13

   ACTION: [PENDING] Michael to create 'RDFa for uF users' on RDFa Wiki
   [recorded in

     [20] http://www.w3.org/2008/09/11-rdfa-minutes.html#action14

   ACTION: [PENDING] Ralph or Steven fix the .htaccess for the XHTML
   namespace [recorded in

     [21] http://www.w3.org/2009/01/08-rdfa-minutes.html#action01

   Ralph: I know Steven poked someone about this

   ACTION: [PENDING] Ralph think about RSS+RDFa [recorded in

     [22] http://www.w3.org/2008/09/11-rdfa-minutes.html#action15

Report on AC Meeting

   Manu: anyone there for the HTML discussions than Ben and Steven?

   Shane: unfortunately Ben couldn't stay for the breakout session

   Mark: the minutes suggest the discussion was quite positive

   Ralph: I needed to participate in a different breakout

   Mark: I'm looking at the minutes of the Backplane XG

   Shane: there appears to be substantial support from the Membership
   for the extensibility model that XHTML has always had

@prefix syntax discussion

   Manu: at our last discussion, Shane and Ralph were favoring the '='
   syntax and Mark and I were favoring the JSON-esque syntax
   ... any new thoughts in the subsequent 2 weeks?

   Mark: I'm involved in a couple of projects where folk are producing
   what they think is RDFa
   ... it's interesting; I see a growing need for tools to check the
   ... simply typos like mismatch between namespace declaration and

   Ralph: no real additional thoughts but I did make note of Mark's
   concerns about the pattern @attr="prefix=value"
   ... but if tools are generating this anyway, how much does it

   Mark: I'm thinking of checking tools more than generation tools

   Manu: definitely think embedded '=' will cause confusion
   ... and people will put whitespace around the '='
   ... so we need resilient syntaxes and parsers

   Shane: I don't think it's terribly important to have delimiters
   other than whitespace between the items
   ... but I won't fight on that
   ... I understand the sensitivity to the repeated '=' issue
   ... do you prefer ':'?

   Manu: yes

   Shane: that's probably fine, but then you end up with repeated ':'

   <ShaneM> perfix="xhv:http:..."

   Shane: I leaned toward repeated '=' in the first place because that
   made it clear which was the prefix and which was the rest

   <markbirbeck> prefix="xhv:xyz dc:xyz"

   <markbirbeck> prefix="xhv=xyz dc=xyz"

   Mark: we're tending to discuss as if [the two examples above] were
   the patterns
   ... this is how @xml:schemalocation works

   <markbirbeck> prefix="

   <markbirbeck> xhv: xyz,

   <markbirbeck> dc: xyz

   <markbirbeck> "

   Mark: I'm thinking we should really be looking at layout such as
   [above in irc]
   ... in this case, additional delimiters are useful; we don't need to
   be compact
   ... we should consider not just a syntax but also examples that
   people will cut & paste
   ... if I were to copy one of Manu's audio prefix examples I could
   select a single line (of many declarations) and insert it into my
   list without introducing error
   ... once you spread things out like this, why not allow further

   <markbirbeck> prefix="

   <markbirbeck> 'xhv': 'xy z',

   <markbirbeck> dc: xyz

   <markbirbeck> "

   Shane: my concern is that URIs allow these characters, so the syntax
   rules and the parsing are both more challenging

   Mark: yes, but there are extra options for delimiting
   ... if we say we're allowing quotes _as well_ this gives additional

   <markbirbeck> prefix="

   <markbirbeck> 'xhv': 'xy z,',

   <markbirbeck> dc: xyz

   <markbirbeck> "

   Mark: if you did have a URI that ends in ',' then quoting allows an
   easy way to include it
   ... ':' in @xmlns was really an effort to find one thing that would
   ... but we have greater flexibility

   Manu: when people mint prefix mapping URIs I find it highly unlikely
   that they'll use a ',' in such a URI
   ... yes, it _could_ happen but if it's a well-known design
   consideration that such characters cause trouble then vocabulary
   developers can avoid them

   Mark: what is the added complexity?

   Manu: it's additional complexity in the parser. I'm questioning
   whether we really need it.

   Mark: it's one regular expression
   ... a way of trying to introduce resilience and something that
   [humans] can grok easily
   ... we come back to this problem of recognizing what is a URI
   ... I'm just thinking of ways to provide resilience when needed
   without mandating it all the time

   <markbirbeck> prefix="

   <markbirbeck> xhv: {xy z,},

   <markbirbeck> dc: xyz

   <markbirbeck> "

   Manu: I'd like to see the regex
   ... my C+sax-based parser doesn't have to use regex's anywhere right

   Mark: a space-separated list needs to be cracked into a list
   ... even '=' can appear in a URI

   <ShaneM> index

   Manu: I don't think we can count on authors writing examples
   ... and a mixture of styles will cause confusion

   Mark: I'm proposing the _possibility_ of permitting this richer
   format, not _requiring_ it

   Manu: I was only questioning whether example authors will really
   write the examples with multi-line declarations

   <markbirbeck> prefix="xhv: xy, dc: xyz"

   Manu: when the examples are written on a single line the richer
   syntax becomes confusing

   Mark: consider space-separated lists

   <markbirbeck> prefix="xhv:xy dc:xyz"

   Mark: then you can't have space around ':'
   ... the options for authors laying out the markup are limited
   ... no flexibility for aligning things [in columns]
   ... whereas the XML attribute syntax has a lot of flexibility, for
   example; can use whitespace to nudge things [into columns]
   ... in terms of consistency, generally in XML spaces are ignored
   ... other than the use in XML Schema to create lists, whitespace is
   not significant

   Shane: whitespace is collapsed, not ignored
   ... this includes newlines
   ... collapsing inside attributes values
   ... however, this is bad; in the HTML DOM whitespace is not
   ... this means a parser that has to work with both XML and HTML has
   to be written to expect multiple whitespace

   Mark: but the presence of whitespace is geenerally not significant
   ... as long as there is whitespace in key places, such as between
   ... '=' vs. ':' is a separate discussion from whether whitespace is
   a delimiter

   Manu: I agree; we shouldn't decide solely on whitespace

   <msporny> prefix="xhv:xy, dc:xyz" prefix="xhv:xy; dc:xyz"

   Manu: for delimiters between mappings, we're considering something
   like ^

   Shane: a lot of our canonical examples are ones that contain ',';
   e.g. Wikipedia or Amazon
   ... places where, for example, an ISBN might be interpolated

   <msporny> prefix="media: [23]http://purl.org/media#, audio:

     [23] http://purl.org/media
     [24] http://purl.org/media/audio

   Mark: yeah, can't quickly come up with an example

   <markbirbeck> mapping, mapping, mapping

   Mark: should treat as mapping, mapping, mapping
   ... then decide what goes inside mapping

   <msporny> prefix="media: [25]http://purl.org/media# ; audio :

     [25] http://purl.org/media
     [26] http://purl.org/media/audio

   Shane: can't just be 'ends in comma' -- must be 'includes comma'

   Manu: are Shane and Ralph ok with using ',' between mappings?

   Shane: if we're going to use ',' or ';' we need to define the
   escaping mechanism
   ... maybe there's already a mechanism defined somewhere
   ... my preferred syntax is identical to schemalocation [i.e.
   alternation] but Ralph says that's a non-starter

   Manu: ok to pick a character that must be URI-encoded in URIs?

   <msporny> [27]http://en.wikipedia.org/wiki/Percent-encoding

     [27] http://en.wikipedia.org/wiki/Percent-encoding

   Mark: every time I look at the URI spec I find it allows more
   characters than I expected
   ... this discussion is pretty much the same discussion the @xmlns
   folk had to go through

   Manu: we could require that reserved characters must be %-encoded
   ... but that makes everything harder

   Mark: and we'd have to avoid a requirement to double-encode
   ... we need a non-reserved character

   Shane: good luck with that!
   ... remember that in the case of CURIE it's a IRI
   ... so even a bigger set of non-reserved character
   ... the only reserved character is space
   ... even schemalocation cheated by not using '=' or ':'; they just
   use alternation
   ... the problem with alternation is that we can't do anything clever
   with default or absent prefixes
   ... but maybe we don't need such rules

   <msporny> prefix="a=b x=y"

   <ShaneM> wow.... we already have this problem!

   Mark: if we needed @prefix on every element then perhaps we might go
   with [the '=' syntax]

   <ShaneM> xmlns:foo="URI" what happens if URI contains a quotation

   Mark: but perhaps we don't need that flexibility; be more
   ... put everything in the head or having a predicate indicating a
   prefix mapping

   Ralhp: predicate as in RDF predicate?

   Mark: yes

   <ShaneM> <meta rel="prefix" name="foo" resource="URI" />

   Mark: however I didn't like that syntax as it puts meta information
   in the same graph as 'ordinary' information, which feels wrong
   ... I'm looking for something that is "cut-and-paste reliable"

   Ralph: Creative Commons would not accept restrictions on where
   mappings can be declared

   Shane: separate two issues; 1. can we provide an alternative to
   @xmlns that would be acceptable beyond the XML community and 2. how
   do we make it easier for our constituents to use RDFa in easier ways
   ... we've talked about having external documents that declare
   ... perhaps even with some well-known prefix declarations
   ... maybe we'll make more progress by not trying to find a single
   solution to these two objectives

   Mark: so do we need a lot of flexibility?
   ... find just enough flexibility for the goals at hand

   <ShaneM> We should try hard to NOT over-engineer this solution
   without having the requirements in mind!

   Manu: the second idea is that there's an @profile value that pulls
   in external mapping declarations

   Mark: 1 is the namespace thing and 2 is ease of authoring

   Shane: consider CSS syntax as an example of going too far; e.g.
   borders on table cells -- totally different behavior depending on
   how many values are supplied

   <markbirbeck> dc: url(xyz)

   Mark: I've just thought of another syntax!

   Ralph: and it may be that the @xmlns problem will go away

   <markbirbeck> Continuing Shane's point, why not 'solve' this:

   <markbirbeck> [28]http://wiki.creativecommons.org/CcREL

     [28] http://wiki.creativecommons.org/CcREL

   Mark: pick an example of something people will frequently want to
   copy and paste; e.g. ccRel
   ... the simple example [in ccRel] is interesting
   ... it just says some other mechanism has defined the token
   ... consider the lengthier scenarios; what other ways are there to
   address these?

   Manu: any of our proposed syntaxes would handle these examples
   fairly cleanly

   <msporny> prefix="a = b x = y"

   Ralph: yeah, it's the ugly corner cases like ',' in URIs that are a

   <msporny> prefix="a=b x=y"

   Shane: even quote is already an issue

   Manu: a simple state machine will handle the '=' syntax

   <ShaneM> prefix="

   <ShaneM> a = b

   <ShaneM> x = y

   <ShaneM> "

   Manu: I see the argument for an extensible syntax that could support
   every use case but I wonder if [that flexiblity] will ever be used
   ... we're trying to solve a very simple problem

   Shane: Mark's desire to make this legible can easily be written
   using the '=' syntax

   <markbirbeck> Shane don't we do this: xmlns:a="&quot;b&quot;"

   Shane: we can easily deal with extra whitespace

   <markbirbeck> a = [29]http://example.org?a=b

     [29] http://example.org/?a=b

   <ShaneM> (.*)\s*=\s*(.*?)\s+

   <markbirbeck> prefix="a = [30]http://example.org?a=b&c=d"

     [30] http://example.org/?a=b&c=d

   Manu: I'm leaning toward preferring this solution
   ... straightforward and easy to implement

   <ShaneM> actually - can't use \s... need [\s\r\n]

   Manu: don't think there's much danger of authors confusing the
   syntax in the markup

   next meeting: 2 weeks (April 16)


   <ShaneM> (.*)[\s\r\n]*=[\s\r\n]*(.*?)[\s\r\n]+

Summary of Action Items

   [PENDING] ACTION: Ben to put up information on "how to write RDFa"
   with screencast possibly and instructions on bookmarklet. [recorded
   in [31]http://www.w3.org/2008/11/06-rdfa-minutes.html#action12]
   [PENDING] ACTION: Jeremy to demonstrate GRDDL with XHTML/RDFa once
   the NS URI is set up. [recorded in
   [PENDING] ACTION: Manu to write summary for Semantic Web Use Cases
   for Ivan. [recorded in
   [PENDING] ACTION: Mark to send Ben ubiquity related wizard stuff
   [recorded in
   [PENDING] ACTION: Mark create base wizard suitable for cloning
   [recorded in
   [PENDING] ACTION: Mark write foaf examples for wiki [recorded in
   [PENDING] ACTION: Michael to create 'RDFa for uF users' on RDFa Wiki
   [recorded in
   [PENDING] ACTION: Ralph or Steven fix the .htaccess for the XHTML
   namespace [recorded in
   [PENDING] ACTION: Ralph think about RSS+RDFa [recorded in

     [31] http://www.w3.org/2008/11/06-rdfa-minutes.html#action12
     [32] http://www.w3.org/2008/09/11-rdfa-minutes.html#action03
     [33] http://www.w3.org/2008/09/11-rdfa-minutes.html#action09
     [34] http://www.w3.org/2008/11/20-rdfa-minutes.html#action11
     [35] http://www.w3.org/2008/09/11-rdfa-minutes.html#action12
     [36] http://www.w3.org/2008/09/11-rdfa-minutes.html#action13
     [37] http://www.w3.org/2008/09/11-rdfa-minutes.html#action14
     [38] http://www.w3.org/2009/01/08-rdfa-minutes.html#action01
     [39] http://www.w3.org/2008/09/11-rdfa-minutes.html#action15

   [DONE] ACTION: Manu to look at
   ec/0037.html about resolving relative URIs [recorded in
   [DONE] ACTION: Mark to review reasoning on setting explicit about=""
   on HEAD and BODY [recorded in

     [40] http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2008Dec/0037.html
     [41] http://www.w3.org/2009/01/08-rdfa-minutes.html#action15
     [42] http://www.w3.org/2008/12/18-rdfa-irc

   [End of minutes]

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