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Re: schema.org Roles design

From: Jason Douglas <jasondouglas@google.com>
Date: Wed, 26 Mar 2014 21:14:05 +0000
Message-ID: <CAEiKvUASwn3Q_h21OLWeM9cCoxC5-G6i83Y7=HjP7Z5KY4jCww@mail.gmail.com>
To: jarno@quantumspork.nl
Cc: guha@google.com, gregg@greggkellogg.net, danbri@google.com, public-vocabs@w3.org
On Wed Mar 26 2014 at 1:59:47 PM, Jarno van Driel <jarno@quantumspork.nl>
wrote:

> Well if @id has the same role as 'itemref' then could there also please be
> some info explaining how that works
>

How did itemref get into this?  That's a microdata-specific DOM-level
mechanism and is totally different.


> , because to be honest, I sort of understand the proposal but am confused
> about @id/itemid. e.g. to me it seems @id functions the same way as
> @resource does in RDFa, or at least that's how I read it.
>
> Wouldn't the Person linking back to the AmericanFootballRole create an
> infinite loop?
>

Graphs have loops.


>
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> On Wed, Mar 26, 2014 at 9:47 PM, Jason Douglas <jasondouglas@google.com>wrote:
>
>> It does play the same role.  I wouldn't be surprised if there are subtle
>> differences in the respective specs, though.
>>
>>
>> On Wed Mar 26 2014 at 1:45:02 PM, Jarno van Driel <jarno@quantumspork.nl>
>> wrote:
>>
>>> Quick question: is '@id' the same in JSON-LD as 'itemid' is in
>>> Microdata?
>>> Because I find it difficult to comprehend the functionality of '@id'.
>>>
>>>
>>> On Wed, Mar 26, 2014 at 9:00 PM, Guha <guha@google.com> wrote:
>>>
>>>> See comments inline
>>>>
>>>>
>>>> On Wed, Mar 26, 2014 at 12:15 PM, Gregg Kellogg <gregg@greggkellogg.net
>>>> > wrote:
>>>>
>>>>> On Mar 26, 2014, at 9:37 AM, Dan Brickley <danbri@google.com> wrote:
>>>>>
>>>>> > At schema.org we have been working on a design for describing roles
>>>>> > and contributions.
>>>>> >
>>>>> > I've just posted a discussion draft in the WebSchemas wiki. Please
>>>>> take a look:
>>>>> >
>>>>> > Roles in Schema.org
>>>>> > https://www.w3.org/wiki/WebSchemas/RolesPattern ->
>>>>> > https://www.w3.org/wiki/images/b/b5/RolesinSchema.org.pdf
>>>>>
>>>>> Some comments on the draft:
>>>>>
>>>>> I think this is a really useful abstraction, but I do see some room
>>>>> for improvement.
>>>>>
>>>>> I think adding date ranges to the role is conflating the role with an
>>>>> event. Better to say that the Joe Montana is the quarterback during the
>>>>> 1992 season of the 49ers by defining an event for the 1992 season. Jason
>>>>> and Jean-Pierre made similar points, and I think that models better.
>>>>>
>>>>> One could look at anything with a temporal extent (including a
>>>> proposition) as an event. It is not clear that buys us much. In fact,
>>>> experience with Cyc shows that this can be confusing.  If you want, you can
>>>> look at Role as a subclass of Event.
>>>>
>>>>
>>>>> A Role seems to use different properties to describe the kind of role
>>>>> ("position", "characterName", "graduationYear"). It might be possible to
>>>>> simply subclass Role so that it's known the kind of role that's being
>>>>> played, but a single property which defines this (ideally an entity, but
>>>>> allowing a string) would be less ambiguous and would avoid falling into the
>>>>> trap of not having considered all of the kinds of roles played. Similarly,
>>>>> settling on a single property to reference the "agent" performing the role
>>>>> might be better than using arbitrary properties from different classes
>>>>> depending on where the role is referenced from. (In fact, you reference the
>>>>> same role from different entities, so context can't really be used either).
>>>>>
>>>>> We don't want to be at either extreme. We don't want overly general
>>>> slots like 'agent, 'performer' and 'object' as the only slots. Similarly,
>>>> we don't want slots like quarterback, runningback, etc.
>>>>
>>>>
>>>>> The schema for hasRole has domainIncludes and rangeIncludes reversed.
>>>>>
>>>>> In the appendix, you site the use of @context as a (temporary) means
>>>>> of describing the range of hasRole to be an entity, not a literal. You
>>>>> could eliminate the context by using an expanded form:
>>>>>
>>>>> {
>>>>>   "@context": "http://schema.org/",
>>>>>   "@type": "Movie",
>>>>>   "name": "Ghostbusters", "hasRole": {
>>>>>     "@type": "MovieRole",
>>>>>     "@id": "movierole_678",
>>>>>     "characterName": "Dr. Peter Venkman",
>>>>>     "actor": {
>>>>>       "@type": "Person",
>>>>>       "name": "Bill Murray",
>>>>>       "hasRole": {"@id": "movierole_678"}
>>>>>     }
>>>>>   }
>>>>> }
>>>>>
>>>>> But, I prefer to use a different property, as "hasRole" does not seem
>>>>> to me to be symetric. Better than defining inverses of every property is to
>>>>> define an inverse alias in the (forthcoming) context. For example:
>>>>>
>>>>>
>>>> Agree.
>>>>
>>>>
>>>>> {
>>>>>   "@context": ["http://schema.org/", {
>>>>>     "inRole": {"@reverse": "hasRole"}
>>>>>   },
>>>>>   "@type": "Movie",
>>>>>   "name": "Ghostbusters", "hasRole": {
>>>>>     "@type": "MovieRole",
>>>>>     "@id": "movierole_678",
>>>>>     "characterName": "Dr. Peter Venkman",
>>>>>     "actor": {
>>>>>       "@type": "Person",
>>>>>       "name": "Bill Murray",
>>>>>       "inRole": "movierole_678"
>>>>>     }
>>>>>   }
>>>>> }
>>>>>
>>>>> This uses the same property "hasRole", but defines a reverse term
>>>>> which will expand, flatten or transform to RDF using the inRole property.
>>>>>
>>>>> Great to see progress on this issue!
>>>>>
>>>>> Gregg
>>>>>
>>>>> >> From the wiki, "For example, when we say that a Person was an actor
>>>>> in
>>>>> > a Movie, we might want to mention their characterName too. When we
>>>>> say
>>>>> > that a SportsTeam has a Person as an athlete, we might want to
>>>>> mention
>>>>> > the position that they play, or the time period in which they
>>>>> > fulfilled that role.".
>>>>> >
>>>>> > I freely acknowledge that PDF isn't the best way to share markup/code
>>>>> > snippets and will copy those into Wiki. However we wanted to get the
>>>>> > draft out asap.
>>>>> >
>>>>> > Here's a quick example extracted from the doc, expressed in JSON-LD.
>>>>> > We want to elaborate on a basic description, so here is the mostasic
>>>>> > version first, followed by the Role-based richer version:
>>>>> >
>>>>> > {
>>>>> > "@context": "http://schema.org/",
>>>>> > "@type": "AmericanFootballTeam",
>>>>> > "name": "San Francisco 49ers",
>>>>> > "athlete": {
>>>>> >   "@type": "Person",
>>>>> >   "name": "Joe Montana"
>>>>> > }
>>>>> > }
>>>>> >
>>>>> > Extended version using Role:
>>>>> >
>>>>> > {
>>>>> >   "@context": "http://schema.org/",
>>>>> >   "@type": "AmericanFootballTeam",
>>>>> >   "name": "San Francisco 49ers",
>>>>> >   "hasRole": {
>>>>> >       "@type": "AmericanFootballRole",
>>>>> >       "@id": "role321",
>>>>> >       "startDate": "1979",
>>>>> >       "endDate": "1992",
>>>>> >       "position": "Quarterback",
>>>>> >       "athlete": {
>>>>> >               "@type": "Person",
>>>>> >               "name": "Joe Montana",
>>>>> >               "hasRole": "role321"
>>>>> >       }
>>>>> >   }
>>>>> > }
>>>>> >
>>>>> > Effectively we interpose a new node in the graph. Instead of
>>>>> >
>>>>> > SanFrancisco49ers ---athlete---> JoeMontana
>>>>> >
>>>>> > We have
>>>>> >
>>>>> > SanFrancisco49ers --hasRole---> [role321] --athlete---> JoeMontana.
>>>>> >
>>>>> > There are a few nearby designs that may be worth discussion here. If
>>>>> > we wanted to make things simpler for publishers, we could remove the
>>>>> > hasRole reference from JoeMontana back to the Role. However this also
>>>>> > makes it harder for consuming applications to understand Role-based
>>>>> > modeling across all domains. Another approach would be to use
>>>>> > different property names for relating the 'subject' and 'predicate'
>>>>> > entities. The appendix in the full proposal document elaborates on
>>>>> > some of these options. I should also note for those of you using the
>>>>> > JSON-LD playground or other generic tools that the above markup needs
>>>>> > some tweaks, since schema.org doesn't yet publish a @context file.
>>>>> > Again, the document has details of a workaround.
>>>>> >
>>>>> > Please take a look. This is quite an important spec for schema.orgas
>>>>> > it has impact across all domains, so it is important to find the
>>>>> right
>>>>> > balance between ease of adoption for publishers, expressivity, ease
>>>>> of
>>>>> > processing etc.
>>>>> >
>>>>> > cheers,
>>>>> >
>>>>> > Dan
>>>>> >
>>>>>
>>>>>
>>>>>
>>>>
>>>
>
Received on Wednesday, 26 March 2014 21:14:35 UTC

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