Dan Brickley announced today that schema.org has added the property "additionalType" to the basic building block, schema.org/Thing. As Brickley says, "The additionalType property makes it possible for Microdata-based publishers to list several relevant types, even when the types are from diverse, independent schemas. This is important for schema.org as it allows our markup to be mixed with other systems, without making it too hard for consuming applications to interpret. A description can use a schema.org type as a base, but mention others (e.g. from DBpedia, Freebase, eventually Wikidata...) to improve the specificity and detail of the description."
As RDFa already allows for use of multiple vocabularies (through the 'typeOf' attribute), it is recommended that RDFa publishers use that native syntax.
In addition to providing additional flexibility to those publishers using Microdata, this change clears a significant obstacle that stood in the way of integrating the popular GoodRelations vocabulary with schema.org. GoodRelations focuses on Product and service descriptions, and because "schema.org/Product" inherits the properties of the parent, "schema.org/Thing," having the additionalType property allows for Microdata-based publishers to utilize -- as Martin Hepp, creator of GoodRelations says -- "the more than 300,000 precise product type identifiers from our http://www.productontology.org service for telling search engines very, very precise the type of products or services you are selling."
Work continues on additions and refinements to schema.org, but this step marks a significant milestone in that work. As Brickley said, "We're not quite at the planned 1.0 release yet but we're getting there!"
Related reading: Microdata or RDFa Lite? Dispelling the Myths
To learn more about this work and to follow the progress of various schema.org proposals, visit: