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Re: Cardinality of schema.org properties

From: Lin Clark <lin.w.clark@gmail.com>
Date: Fri, 21 Oct 2011 10:04:56 +0100
Message-ID: <CACho_At3PPtLZ-4sZijZgt83MtHihEs56ijEVu=2stdUyNG7VA@mail.gmail.com>
To: Dan Brickley <danbri@danbri.org>
Cc: John Panzer <jpanzer@google.com>, public-vocabs <public-vocabs@w3.org>
I have to say, I think this is going to be really confusing as time goes on.

For example, Schema.org already defines a 'video' term for CreativeWork.
However, Google's Software Application itemtype introduces a 'videos' term,
presumably because they want to indicate that an app can have multiple
videos. This means that the Software Application has both a 'video' property
and a 'videos' property.

Also, for a property such as 'videos', which takes an item as it's value,
the itemprop attribute must be placed on the singular... on the div that
defines that singular item. I think it's a little strange to have a plural
property on a singular and will probably lead publishers to use microdata as
they would RDFa... in fact, this already happens in a Goodreads snippet
that Jayson Lorenzen posted on the HTML data TF list:

<div class="infoBoxRowItem" itemprop='awards'>
   <a href="/award/show/9-hugo-award" class="award">Hugo Award for Best
Novel (1985)</a>, <a href="/award/show/23-nebula-award" class="award">Nebula
Award for Best Novel (1984)</a>, <a
href="/award/show/326-philip-k-dick-award" class="award">Philip K. Dick
Award (1984)</a>, <a href="/award/show/1403-john-w-campbell-memorial-award"
class="award">John W. Campbell Memorial Award Nominee for Best Science
Fiction Novel (1985)</a>

The awards should be placed on each individual link, not the wrapping div.
However, I can't blame the Goodreads developer for not understanding that.

My opinion is that terms should be singular. This communicates much more
clearly how they should be used in microdata... if it's a choice between
having data that can't be properly parsed or having data that breaks
implicit cardinality rules, I would take the later.


On Thu, Oct 20, 2011 at 6:32 AM, Dan Brickley <danbri@danbri.org> wrote:

> On 20 October 2011 01:22, John Panzer <jpanzer@google.com> wrote:
> > I'm trying to determine how to know what the intended cardinality of any
> > given schema.org defined property.
> > Some (such as "name" and "url") appear to be defined in English as
> appearing
> > at most once.  Semantically, having them appear multiple times would
> appear
> > problematic.
> > Some, such as "tracks", appear to be explicitly defined as multivalued
> and
> > indeed need an ordering (see
> > also
> http://lists.w3.org/Archives/Public/public-html-data-tf/2011Oct/0004.html
> ).
> >
> > Is this a correct interpretation?  How would one determine whether
> something
> > is potentially multivalued or not based on the spec?
> In http://schema.org/docs/extension.html it is explicitly linked to
> natural language plurality, as you suggest:
> "Note on naming conventions
> Schema.org uses the following naming convention. We request that you
> follow this naming convention for your extensions as well.
> Types and Enumerations start with a capital letter and are CamelCase.
> Properties start with a lower case letter and are also camelCase.
> Properties that can take multiple values (such as parents) are plural
> and those that can take only a single value (such as dateOfBirth) are
> singular."
> Looking at http://schema.org/MusicPlaylist
> http://schema.org/MusicRecording and nearby, it could certainly be
> clearer about ordering. Investigating...
> Dan

Lin Clark
DERI, NUI Galway <http://www.deri.ie/>

Received on Friday, 21 October 2011 09:05:29 UTC

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