AdditionalType was: audiobook options in objects

Hi All,

I’ve pulled this out of the audiobook thread as I think it is generally
applicable to several areas of our discussions.

Karen’s points below highlight several points relevant to this, which I will
try to clarify.

This emerged from the audiobook thread as audio book is a good example of
something in our domain of multiple types ­ a creative work, possibly a
book, with a file format (WMA, MP3, etc), and a physical form (CD, cassette
tape, etc.).  That thread has moved on and we proposing a new sub-type of
CreativeWork ­ AudioBook, which I agree with.  For the purposes of examples
in this email am presuming that proposal has been accepted.

Starting with Karen’s second question:
> Second, it still isn't clear, however, if you have multiple associatedMedia
> fields, e.g. A, B and C, whether that means that you have that CW in three
> different media, or if you have the CW in a single medium that is defined as
> A+B+C.

She is referencing multiple instances of a property, however I believe it is
the same question for multiple types.

It is an AND relationship.

The turtle syntax is really helpful for envisioning multiple types:
    <http://example.com/1234>
        a schema:Audiobook, pto:Windows_Media_Audio, pto:Compact_Disk;

Which can be unpacked as:
    <http://example.com/1234>
        a schema:Audiobook;
        a pto:Windows_Media_Audio;
        a pto:Compact_Disk;

Which can be read as:
    <http://example.com/1234> is the identifier for a thing which is
        a Audiobook and,
        a Windows_Media_Audio, and
        a Compact_Disk

If you want to describe something (an audio book) that is available in
several formats, you are describing relationships between different things.

Against my better judgement and dipping into FRBR language to explain it....

You would have the description of an Expression, of type Audiobook, with
links to instances (Manifestations) for each format. Each instance would be
a combination of Audiobook and Compact_Disc; Audiobook and DVD; Audiobook
and Cassette; etc.

Check out the examples library
A0<http://www.w3.org/community/schemabibex/wiki/Examples/mylib/A0>
(Expression) and its related instances (Manifestations)
A1<http://www.w3.org/community/schemabibex/wiki/Examples/mylib/A1> and
A3<http://www.w3.org/community/schemabibex/wiki/Examples/mylib/A1> to see
how this might be encoded.



Moving on to how we encode multiple types for a thing there are a couple of
issues to address.

Firstly, the differences between RDF (Turtle), RDFa, and Microdata.

* RDF is the most obvious ­ as per the above example you just keep adding
type statements as required.
*  RDFa add the type URI to the ‘typeof’ attribute:
>     <div vocab="http://schema.org/"
>         typeof="Audiobook http://www.productontology.org/id/Compact_Disk">
* Microdata is a little more difficult as the microdata standard does not
natively support multiple types.  To overcome this limitation Schema
introduced the addtionalType property so that they could encode this concept
using microdata, thus:
>     <div itemscope itemtype="http://schema.org/Audiobook">
>         <link itemprop="additionalType"
> href="http://www.productontology.org/id/Compact_Disk">

The fact that the microdata solution uses additionalType as the property
name introduces the impression that the other type(s) are somehow
subordinate.  Maybe it would have been better to have ‘alsoOfType’ as a
property name.   

The important effect of this approach is that there is no relevance in the
order of their declaration.  For instance a librarian may describe an
audiobook on CD in microdata thus:
<div itemscope itemtype="http://schema.org/Audiobook">
>   <link itemprop="additionalType"
> href="http://www.productontology.org/id/Compact_Disk">

Whereas a retailer may describe the same thing as:
<div itemscope itemtype="http://www.productontology.org/id/Compact_Disk">
>   <link itemprop="additionalType" href=" http://schema.org/Audiobook">
> 
These are both valid and equivalent to each other.


~Richard


On 09/02/2013 20:09, "Karen Coyle" <kcoyle@kcoyle.net> wrote:

> Owen, I take your point: additionalType seems to be sub-typing
> CreativeWork, not adding information about the product. I vaguely recall
> having been warned about additionalType -- that it is not often used and
> seems to be tricky. Here's the definition of "aT":
> 
> "An additional type for the item, typically used for adding more
> specific types from external vocabularies in microdata syntax. This is a
> relationship between something and a class that the thing is in. In RDFa
> syntax, it is better to use the native RDFa syntax - the 'typeof'
> attribute - for multiple types. Schema.org tools may have only weaker
> understanding of extra types, in particular those defined externally."
> 
> Richard posted this in an email: [1]
> "
> Sticking with the Product Ontology approach for a moment ­ an audiobook
> in WMA on a cd would just be a combination of multiple types thus:
>>  > http://schema.org/Book
>>  > additionalType: http://www.productontology.org/id/Audiobook
>>  > additionalType: http://www.productontology.org/id/ Windows_Media_Audio
>>  > additionalType: http://www.productontology.org/id/ Compact_Disc
>>  >
> 
> First, I think that "/associatedMedia" in CreativeWork looks to be a
> better fit for this. It is defined as: "The media objects that encode
> this creative work. This property is a synonym for encodings."
> 
> Second, it still isn't clear, however, if you have multiple
> associatedMedia fields, e.g. A, B and C, whether that means that you
> have that CW in three different media, or if you have the CW in a single
> medium that is defined as A+B+C. I believe that Richard's example above
> was the latter. You seem to be concerned about encoding the former.
> Surely we need to be able to distinguish between them. I believe that
> means moving toward item or offer-level description for the different
> encodings. I can't think of any other way to make it clear.
> 
> kc