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Re: Some interesting things that show up when using a reasoner to classify schema.org

From: Dan Brickley <danbri@google.com>
Date: Thu, 22 Jan 2015 19:31:26 +0000
Message-ID: <CAK-qy=6JBx799Nj4J+qanTfh9WHxOmTdRQiSQtHGJ6kmfvnnyw@mail.gmail.com>
To: Simon Spero <sesuncedu@gmail.com>
Cc: Gregg Kellogg <gregg@greggkellogg.net>, ☮ elf Pavlik ☮ <perpetual-tripper@wwelves.org>, W3C Web Schemas Task Force <public-vocabs@w3.org>, Martin Hepp <martin.hepp@unibw.de>
On 22 January 2015 at 19:15, Simon Spero <sesuncedu@gmail.com> wrote:
> On Jan 22, 2015 1:31 PM, "Gregg Kellogg" <gregg@greggkellogg.net> wrote:
>>
>> The difference between using the unionOf and domainIncludes variation is
>> that domainIncludes is open, and allows other vocabularies to extend the
>> domain for their purpose (as, for example, yoursports.com does). Whereas,
>> unionOf uses an rdf:List, which can't be extended. Other than the
>> extensibility issues, then domain/rangeIncludes are essentially the same as
>> unionOf.
>
> That is one of at least two possible interpretations;
>
> (1) domainIncludes statements are simply documentation, so that all domains
> are :Thing, and all ranges are ( :Thing or :DataType ) ; OR
>
> (2) domainIncludes for a given time interval form a closed union.

More the latter. It's a kind of "saying less than we might" to leave
room for things to change.

In practice, most of the schema is mostly not changing most of the time.

> When the bicycling guitarist was flagged by the Google rich snippet testing
> tool for using the genre property on MusicGroup, after a domainIncludes had
> been added to the schema, but before the tool had been modified, it strongly
> suggests that the interpretation adopted by Google is (2).

The Google tooling is oriented towards helping publishers get their
markup in a form that will be understood and used. It might sometimes
use stricter sounding language than is formally justified by the
underlying specs. There is also room for improvement around the
possibility of things having multiple types (Book + Product being the
canonical...).  Neither schema.org nor the Google tooling says much
about that right now, although it is a useful option for decoupling
awkward overlaps.

Dan

> Note that if the domain of a property is specified to be a  ( possibly
> union) class, but ought be applicable to some thing that cannot an instance
> of that class, then there is an error- either in the definition of the
> property, the class, or in the specification of its domain.
>
> Note that subclassing is still applicable.
>
> Simon
Received on Thursday, 22 January 2015 19:31:54 UTC

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