The schema.org official blog has announced support for enumerated lists. Adding this support allows developers using schema.org to use selected externally maintained vocabularies in their schema.org markup. According to the W3C-hosted schema.org WebSchemas wiki, "This is in addition to the existing extension mechanisms we support, and the general ability to include whatever markup you like in your pages. The focus here is on external vocabularies which can be thought of as 'supported' (or anticipated) in some sense by schema.org."
In other words, "Schema.org markup uses links into well-known authority lists to clarify which particular instance of a schema.org type (eg. Country) is being mentioned."
We caught up with Dan Brickley of schema.org to ask about the new external lists work and how schema.org would manage support for the various vocabularies out there. Brickley responded, "As ever, it's a balancing act. If we have a giant undocumented mush of thousands of would-be authorities, that isn't so helpful for publishers/webmasters - and ease of use for those folk is top of our list. On the other hand, we don't want to be a centralised bottleneck, slowly hand-reviewing a tiny, pedantically-reviewed list of 'approved' vocabularies...It's clear the sweet-spot is somewhere in the middle between the two. We'll work out quite what that means over time, and as pragmatically as ever. So we start with some common 'no-brainer' authorities, like plugging in Wikipedia, and on topics like 'Country' which are an obvious case for externally maintained lists."
One important distinction is between what is possible for developers to publish in their markup today vs. what the various search engines will necessarily recognize and do with that data.
Webmasters will eventually find at schema.org some combination of data, tools, and APIs to make it easier to find controlled values from the externally maintained vocabularies. In the meantime, now is a time to gain first-mover advantage, so that as the search engines and other systems do begin to look for specific vocabularies and types of data markup across the web, those sites who have already integrated that data will be ready.
It is early days still, and for now, anyone interested in joining the discussion about external list support is encouraged to do so via the "public-vocabs" mailing list maintained by the W3C. More information on this group and signing up for the mailing list is available at: http://www.w3.org/wiki/WebSchemas.
Given this announcement about enumerated lists in schema.org, and the recent launch of the Wikidata project, which could become a strong source for such lists, it's worth considering the intersection of the two efforts. That connection was explored recently in this post.[Editor's Note: We will be discussing much more about the latest schema.org developments with the core schema.org team (from Google, Yahoo, Bing, and Yandex as well as the W3C and user organizations) at #SemTechBiz. Early rates expire today, May 14. Register today and save $200.]