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Re: Updates to HTML+RDFa 1.1

From: Niklas Lindström <lindstream@gmail.com>
Date: Mon, 7 Jan 2013 09:47:24 +0100
Message-ID: <CADjV5jcJ_OqaKQW57jqkQnxydD=s-Cjd+ya5LdMuihwZji9Q1w@mail.gmail.com>
To: Manu Sporny <msporny@digitalbazaar.com>
Cc: RDFa WG <public-rdfa-wg@w3.org>

On Mon, Jan 7, 2013 at 3:14 AM, Manu Sporny <msporny@digitalbazaar.com> wrote:
> Hi folks,
> Gregg and I discussed the Reference Folding feature a bit today and then
> I went through and "refined" the text a bit. Readers will have to let us
> know if it is an improvement or not.
> http://www.w3.org/2010/02/rdfa/sources/rdfa-in-html/Overview-src.html
> High-level changes:
> 1. Renamed the feature from "Reference Folding" to "Property Copying".
> 2. Got rid of "rdfa:Prototype" as you may want to copy properties from
>    something that isn't an rdfa:Prototype.

But how do you distinguish what to copy and what not to copy? There is
a danger of conflation here, where something like group data is merged
into an event, where these are most definitely distinct entities.
Also, this seems to copy the rdf:type of the formerly prototypical
object? That doesn't work with the examples given (a MusicEvent is not
a PerformingGroup, a Person is not a MusicGroup).

The good thing about prototypes was that such abstract entities
represent sets of shared, disconnected characteristics shared by
multiple other entities. Also, it *is* an abstract concept, which
sends a signal that users are doing something more advanced, and
should consider whether a simple repetition of data is simpler (since
in actuality it *is* repeated).

> 3. Changed "rdfa:ref" to "rdfa:include".

While I was unsure about the name "ref", I'm not sure if "include"
paints a clearer picture unless the thing included *is* a prototype.
Since this feature works on the semantic level, not the syntactic, we
need to be careful with terminology.

> 4. Removed the pass that removes the "prototype" features, as that may
>    not be what the author always wants to do. For example, if you have
>    a base model for something like a car, you don't want to delete
>    it from the data as the knowledge of what the base model is can be
>    useful.

I wasn't sure about whether to remove prototypical objects as it
worked previously, since keeping them would preserve the nature of the
copying (and you could basically revert it to save "semantic space").
With these changes it's obviously bad to remove data. But as said, I
think the reliance on "concrete" resources from which to copy all
descriptions is troublesome.

> 5. Based on feedback from Bruce Lawson of Opera, I changed the first
>    example to be a little more accessible.
> 6. I removed the use of bnodes in the examples because bnodes scare
>    people.

I thought they made sense, at least with prototypes, since the
involved resource is quite abstract (bordering on syntactic). I'd
rather that those scared of bnode id:s don't use advanced features
like this. ;)

> Thoughts?

In summary, I'm not entirely comfortable with this new form of the
feature. I fear it is too sweeping. For one, if included
characteristics are themselves concrete entities, I think copying the
entire description of them into the facts about other, probably
related, objects will lead to quite strange data. Model-wise, you
stand the risk of a too broad inclusion and conflation. Referentially,
as these objects probably relate to one another, "including" e.g. a
super-event in a subEvent may lead to a self-referential subEvent
relation or similar (which isn't the worst thing semantically, but may
lead to strange behavior by interpreting programs).

In general, any kind of copying feature is something I want to treat
with care. We received no requirements for it up until recently. Of
those, some of them can instead be solved by abstract entities in the
modeling, some repeat so little data that a built-in copying feature
seems unnecessary. And in general, where multiple facts are to be
repeated for many things, the conceptually shared entity is nothing
more than a prototype, which is why I like that notion to be part of
the feature.

I will mull over this some more of course.


> -- manu
> --
> Manu Sporny (skype: msporny, twitter: manusporny)
> Founder/CEO - Digital Bazaar, Inc.
> blog: The Problem with RDF and Nuclear Power
> http://manu.sporny.org/2012/nuclear-rdf/
Received on Monday, 7 January 2013 08:48:21 UTC

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