W3C home > Mailing lists > Public > public-vocabs@w3.org > March 2014

Re: schema.org Roles design

From: Jarno van Driel <jarno@quantumspork.nl>
Date: Wed, 26 Mar 2014 21:59:46 +0100
Message-ID: <CAFQgrbayTAWBErBR_YMDmuyEUQRJfHNwpU9Hae+TkEx5xFBCnQ@mail.gmail.com>
To: Jason Douglas <jasondouglas@google.com>
Cc: Guha <guha@google.com>, Gregg Kellogg <gregg@greggkellogg.net>, Dan Brickley <danbri@google.com>, W3C Web Schemas Task Force <public-vocabs@w3.org>
Well if @id has the same role as 'itemref' then could there also please be
some info explaining how that works, 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?






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.org as
>>>> > 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 21:00:14 UTC

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