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Re: Indicating main entity / primaryTopic - proposal to use 'schema.org/about'

From: Dan Brickley <danbri@google.com>
Date: Wed, 21 May 2014 20:22:11 +0100
Message-ID: <CAK-qy=5tTB3Si76UZHZRSgUG+MyoXm4rxW0a+vcbaTb-P=k=aA@mail.gmail.com>
To: Dan Scott <dan@coffeecode.net>
Cc: Jarno van Driel <jarnovandriel@gmail.com>, Jocelyn Fournier <jocelyn.fournier@gmail.com>, W3C Web Schemas Task Force <public-vocabs@w3.org>
On 21 May 2014 19:21, Dan Scott <dan@coffeecode.net> wrote:
> On Wed, May 21, 2014 at 02:04:20PM +0200, Jarno van Driel wrote:
>>
>> I was wondering, can an entity also have multiple @about properties?

That's the right question to be asking. And I didn't ask it hard
enough yesterday (probably because I wouldn't have liked the answer).

The wording http://schema.org/about has currently, "The subject matter
of the content." is awkward. The word "the" suggests a single thing is
the subject matter, but it is vague enough that you could have several
entities via repeated properties together capturing "the subject
matter".

What I think we want is a property that performs the same role as
FOAF's 'primaryTopic': it should point to at most one entity/thing.
Given currently popular terminology we might call it 'mainEntity' as a
strawman.

I was hoping we could get away with refining the interpretation of
'about', but I'm coming around to the view that it has been used in
too many diverse ways over the last 3 years for that to work.

>> I ask because when chaining multiple entities to a WebPageElement, to me
>> it
>> seems the following is the logical thing to do:
>>
>> <body itemscope itemtype="http://schema.org/WebPage">
>>    ...
>>    <div itemprop="hasPart" itemscope
>> itemtype="http://schema.org/WPSideBar">
>>        <div itemprop="about" itemscope
>> itemtype="http://schema.org/ContactPoint">...</div>
>>        <div itemprop="about" itemscope
>> itemtype="http://schema.org/ItemList">...</div>
>>    </div>
>>    ...
>> </body>
>>
>> Or would @hasPart or @mentions be prefered over @about?

I don't think they're great examples of about-ness, except
ContactPoint, if the page is indeed about contact info. The
stereotypical use for 'about' is a specific person-place-or-thing that
the content is 'about'. Sidebars and lists are structural mechanisms;
it would be more typical to see Product, Book, Person, Place etc used.
However your main point, that 'about' could credibly be repeated given
its definition, is quite reasonable.

>
> I'm not going to offer any advice about whether "hasPart" or "mentions"
> might be preferred here, but you can certainly have multiple "about"
> properties for a single entity.

Yeah. It is tempting to defend a strict reading of the word 'the' and
claim it shouldn't _really_ be repeated; but I don't think that's
credible.

> See the example for http://schema.org/MedicalScholarlyArticle - "about"
> is used twice, because the article is about a type of drug and
> about a type of medical condition.

quite :)


> The cardinality of schema.org properties appears to be a FAQ dating back
> to at least 2011 (http://www.w3.org/2011/webschema/track/issues/5); we
> should probably add an explicit statement to
> http://schema.org/docs/gs.html or http://schema.org/docs/faq.html (or
> both) saying that you can, in general, repeat properties in schema.org
> entities as necessary.

There are a few (e.g. birthDate, deathDate, most boolean-valued
properties) that have at most one sensible value. However even those
might have several reasonable encodings. And there are some, e.g.
iataCode hopefully, for which there should be at most one entity that
has any given value for that property. However we've not attempted
cataloguing these cases, partly through a concern to avoid making
unrealistically brittle and rigid rules that will be ignored...

cheers,

Dan
Received on Wednesday, 21 May 2014 19:22:38 UTC

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