Re: Schema.org property cardinality and use of plural (WAS Re: SoftwareApplication proposal for schema.org)

I had the same question when I first started looking at this.  There is a
certain simplicity in not requiring microdata vocabularies to define
cardinality of properties, and leaves the door open to interesting use
cases that may not have been initially imagined.

That said, there is the practical need for implementors to make a decision
on how they're going to handle multiple occurrences of properties which
they assumed to be singular.  What happens when a Person has multiple name
properties?  It's up to each implementor to decide, and the worse case is
for drastically different implementations to arise such that publishers
don't know what to expect.

I would love to see cardinality take the same approach as types.  From the
conformance section of http://schema.org/docs/datamodel.html:

While we would like all the markup we get to follow the schema, in
> practice, we expect a lot of data that does not. We expect schema.orgproperties to be used with new types. We also expect that often, where we
> expect a property value of type Person, Place, Organization or some other
> subClassOf Thing, we will get a text string. In the spirit of "some data is
> better than none", we will accept this markup and do the best we can.


I think the same would apply to cardinality.  We provide guidance on
expected cardinality of properties, but always do the best we can with
whatever we get.

To address the original question, I think singular and plural naming of
properties is certainly one way (though not the only way) to imply the
expected cardinality of a particular property.  Yes, you get the somewhat
unusual mismatch of naming each individual instance with a plural name, but
you're always going to run into this certain cases.  If were you use
singular naming, you get weird results when you following the specified
JSON mapping:

{
  "type": "http://schema.org/Person",
  "properties": {
    "child": [ { ... }, { ... } ]
  }
}

This same problem occurred with PortableContacts when you compare the XML
and JSON representations:
http://portablecontacts.net/draft-schema.html#anchor5.  For what it's
worth, PoCo used plural naming where properties were expected to be
multi-valued.  Unfortunately, we already have examples in Schema.org where
properties that I would expect to be plural have a singular name (i.e.
Person/affiliation).

-will

On Fri, Feb 24, 2012 at 10:26 AM, Evain, Jean-Pierre <evain@ebu.ch> wrote:

> hi Dan,
>
> it is clear from the example provide that usging plural is not correct as
> each instance of operatingsystems points to one unique object.
>
> Those who tend to use plural make it optional followed by an individual
> with cardinality one to many
>
> But this is quite ugly for ontologies. ( IMHO)
>
> JP
> ________________________________________
> From: Dan Brickley [danbri@danbri.org]
> Sent: 24 February 2012 17:04
> To: Lin Clark
> Cc: Adrian Giurca; public-vocabs@w3.org
> Subject: Re: Schema.org property cardinality and use of plural (WAS Re:
>  SoftwareApplication proposal for schema.org)
>
> On 24 February 2012 16:33, Lin Clark <lin.w.clark@gmail.com> wrote:
> > Looking at this brought up a previous question. I see that properties
> such
> > as operatingSystems are given plural names. However, it could look
> confusing
> > in microdata.
> >
> > For example:
> >
> > <div itemscope="" itemtype="http://schema.org/SoftwareApplication">
> > <ul>
> >   <li itemprop="operatingSystems">OSX 10.6</li>
> >   <li itemprop="operatingSystems">Windows 7</li>
> > </ul>
> >
> > This was previously brought up in Issue 5, and I pointed out the kinds of
> > confusion using the plural in that way might cause for content authors.
> Has
> > there been any further discussion?
>
> There has been a bit of discussion, but nothing conclusive.
>
> What do others here think? Is schema.org's use of plural properties
> problematic enough that people want a change?
>
> I don't have a complete list but for example
>
> * http://schema.org/CreativeWork has 'reviews' pointing to a 'Review
> -- Review of the item.'
> * or 'encodings' -> 'The media objects that encode this creative
> work'. (It also has 'offers' and 'mentions' but those have a
> non-plural reading)
> * http://schema.org/Movie has 'actors', which takes (Person) 'A cast
> member of the movie, TV series, season, or episode, or video.'
> * and also 'director' (Person), 'The director of the movie, TV
> episode, or series.'.
>
> Anyone care to make a complete list of these?
>
> Dan
>
>
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