Content-Carrier

Content-Carrier Proposal

Status: Draft
Author: Richard Wallis

Overview

In early examples (OCLC WorldCat.org, for example) difficulties were experienced in expressing the differentiation between content and carrier types of material/format/medium in bibliographic descriptions. In an attempt to address the problem it was proposed at that time to create new Types for things such as Computer File, Game, Image, Interactive Multimedia, Kit, Musical Score, Newspaper, Periodical, Thesis, Toy, Video, VideoGame, Visual Material, Web Site, etc.

There was consensus that this approach would not scale tending to a) overload Schema with new types, and b) requiring a Schema adoption process for each new type.

The use of enumerations was also considered either internal (within Schema such as with BookFormatType) or external. Both of these have the challenge of defining which organisation or community mangages such lists, either Schema for internal or some other body for external instances.

However we do need a simple, Schema.org style, way of identifying that a CreativeWork or sub-type is, for instance, an audio book on CD.

Proposal

It is proposed that when describing a CreativeWork, or a sub-type thereof, an additional type corresponding to the type of material and/or carrier is applied to the description using the additionalType property (for Microdata markup) or typeof (for RDFa).

The The Product Types Ontology, which publishes URIs for high-precision identifiers for product types based in Wikipedia, should be recommended as significant source for URI identifiers for these types.

The use of The Product Types Ontology as a source for URIs to identify material and carrier types alleviates the need for any organisation or body to manage or govern a continuously evolving list of types. As the source types are derived from Wikipedia, the creation of previously undefined types is a matter of creating a Wikipedia page for that type then using it to query the Product Ontology site. Similarly the descriptions of the types, used on the Product Ontology documentation pages can be community managed via the source Wikipedia pages.

This proposal does not discourage the use of URIs from other sources to identify types of things, however it does recommend the principle of only using a URI for a type that is defined as a sub-type of Schema:Thing as Product Ontology does by creating all its identifiers as a sub-type of Schema:Product. It is only in that way that they can be used as additional types.

In that way this approach also has the benefit of not requiring any extensions to Schema.org.

Examples

An audio book in CD format:

Before:

<div>
  Dune /  by <a href="http://viaf.org/viaf/59083797">Frank Herbert</a>
 
  ISBN-10: 1427201439<br/>
  Type:    Audio Book <br/>  
  Format:  Compact Disk <br/>
 
  <p>Other descriptions:</p>
  <p>
    (WorldCat.org)<a href="http://www.worldcat.org/oclc/153312079">Dune</a>
  </p>
</div>

Microdata:

<div itemscope itemtype="http://schema.org/Book">
  <link itemprop="additionalType" href="http://www.productontology.org/id/Audiobook">
  <link itemprop="additionalType" href="http://www.productontology.org/id/Compact_Disk">

  <span itemprop="name">Dune</span> /
  by <a itemprop="author" href="http://viaf.org/viaf/59083797">Frank Herbert</a>
 
  ISBN-10: <span itemprop="isbn">1427201439</span> <br/>
  Type:    Audio Book<br/>  
  Format:  Compact Disk <br/>
 
  <p>Other descriptions:</p>
  <p>
    (WorldCat.org)<a itemprop="sameThingAs" href="http://www.worldcat.org/oclc/153312079">Dune</a>
  </p>
</div>

RDFa:

 <div vocab="http://schema.org/"
      typeof="Book http://www.productontology.org/id/Audiobook http://www.productontology.org/id/Compact_Disk">
  <span property="name">Dune</span> /
  by <a property="author" href="http://viaf.org/viaf/59083797">Frank Herbert</a>
 
  ISBN-10: <span property="isbn">1427201439</span> <br/>
  Type:    Audio Book <br/>  
  Format:  Compact Disk <br/>
 
  <p>Other descriptions:</p>
  <p>
    (WorldCat.org): <a property="sameThingAs" href="http://www.worldcat.org/oclc/153312079">Dune</a>
  </p>
 </div>

Turtle:

@prefix schema: <http://schema.org/> .
@prefix schemap: <http://proposed-schema.org/> .
@prefix pto: <http://www.productontology.org/id/> .

[] a schema:Book, pto:Audiobook, pto:Compact_Disk;
    schema:name "Dune";
    schema:author <http://viaf.org/viaf/59083797>;
    schema:isbn "1427201439";
    schemap:sameThingAs <http://www.worldcat.org/oclc/153312079> .