Schema.org is basically a simple vocabulary for describing stuff, on the web. Embed it in your html and the search engines will pick it up as they crawl, and add it to their structured data knowledge graphs. They even give you three formats to chose from — Microdata, RDFa, and JSON-LD — when doing the embedding. I’m assuming, for this post, that the benefits of being part of the Knowledge Graphs that underpin so called Semantic Search, and hopefully triggering some Rich Snippet enhanced results display as a side benefit, are self evident.
The vocabulary itself is comparatively easy to apply once you get your head around it — find the appropriate Type (Person, CreativeWork, Place, Organization, etc.) for the thing you are describing, check out the properties in the documentation and code up the ones you have values for. Ideally provide a URI (URL in Schema.org) for a property that references another thing, but if you don’t have one a simple string will do.
There are a few strangenesses, that hit you when you first delve into using the vocabulary. For example, there is no problem in describing something that is of multiple types — a LocalBussiness is both an Organisation and a Place. This post is about another unusual, but very useful, aspect of the vocabulary — the Role type.
At first look at the documentation, Role looks like a very simple type with a handful of properties. On closer inspection, however, it doesn’t seem to fit in with the rest of the vocabulary. That is because it is capable of fitting almost anywhere. Anywhere there is a relationship between one type and another, that is. It is a special case type that allows a relationship, say between a Person and an Organization, to be given extra attributes. Some might term this as a form of annotation.
So what need is this satisfying you may ask. It must be a significant need to cause the creation of a special case in the vocabulary. Let me walk through a case, that is used in a Schema.org Blog post, to explain a need scenario and how Role satisfies that need.
Starting With American Football
Say you are describing members of an American Football Team. Firstly you would describe the team using the SportsOrganization type, giving it a name, sport, etc. Using RDFa:
So we now have Chucker Roberts described as an athlete on the Touchline Gods team. The obvious question then is how do we describe the position he plays in the team. We could have extended the SportsOrganization type with a property for every position, but scaling that across every position for every team sport type would have soon ended up with far more properties than would have been sensible, and beyond the maintenance scope of a generic vocabulary such as Schema.org.
This is where Role comes in handy. Regardless of the range defined for any property in Schema.org, it is acceptable to provide a Role as a value. The convention then is to use a property with the same property name, that the Role is a value for, to then remake the connection to the referenced thing (in this case the Person). In simple terms we have have just inserted a Role type between the original two descriptions.
This indirection has not added much you might initially think, but Role has some properties of its own (startDate, endDate, roleName) that can help us qualify the relationship between the SportsOrganization and the athlete (Person). For the field of organizations there is a subtype of Role (OrganizationRole) which allows the relationship to be qualified slightly more.
So far I have just been stepping through the example provided in the Schema.org blog post on this. Let’s take a look at an example from another domain – the one I spend my life immersed in – libraries.
There are many relationships between creative works that libraries curate and describe (books, articles, theses, manuscripts, etc.) and people & organisations that are not covered adequately by the properties available (author, illustrator, contributor, publisher, character, etc.) in CreativeWork and its subtypes. By using Role, in the same way as in the sports example above, we have the flexibility to describe what is needed.
Take a book (How to be Orange: an alternative Dutch assimilation course) authored by Gregory Scott Shapiro, that has a preface written by Floor de Goede. As there is no writerOfPreface property we can use, the best we could do is to is to put Floor de Goede in as a contributor. However by using Role can qualify the contribution role that he played to be that of the writer of preface.
<span property="roleName"src="http://id.loc.gov/vocabulary/relators/wpr">Writer of preface</span>
<span property="contributor"src="http://http://viaf.org/viaf/283191359">Floor de Goede</span>
You will note in this example I have made use of URLs, to external resources – VIAF for defining the Persons and the Library of Congress relator codes – instead of defining them myself as strings. I have also linked the book to it’s Work definition so that someone exploring the data can discover other editions of the same work.
Do I always use Role? In the above example I relate a book to two people, the author and the writer of preface. I could have linked to the author via another role with the roleName being ‘Author’ or <http://id.loc.gov/vocabulary/relators/aut>. Although possible, it is not a recommended approach. Wherever possible use the properties defined for a type. This is what data consumers such as search engines are going to be initially looking for.
One last example
To demonstrate the flexibility of using the Role type here is the markup that shows a small diversion in my early career:
@prefix schema:<http://schema.org/> .
This demonstrates the ability of Role to be used to provide added information about most relationships between entities, in this case the employee relationship. Often Role itself is sufficient, with the ability for the vocabulary to be extended with subtypes of Role to provide further use-case specific properties added.
Whenever possible use URLs for roleName In the above example, it is exceedingly unlikely that there is a citeable definition on the web, I could link to for the roleName. So it is perfectly acceptable to just use the string “Keyboards Roadie”. However to help the search engines understand unambiguously what role you are describing, it is always better to use a URL. If you can’t find one, for example in the Library of Congress Relater Codes, or in Wikidata, consider creating one yourself in Wikipedia or Wikidata for others to share. Another spin-off benefit for using URIs (URLs) is that they are language independent, regardless of the language of the labels in the data the URI always means the same thing. Sources like Wikidata often have names and descriptions for things defined in multiple languages, which can be useful in itself.
Final advice This very flexible mechanism has many potential uses when describing your resources in Schema.org. There is always a danger in over using useful techniques such as this. Be sure that there is not already a way within Schema, or worth proposing to those that look after the vocabulary, before using it.
Good luck in your role in describing your resources and the relationships between them using Schema.org
Google announced yesterday that it is the end of the line for Freebase, and they have “decided to help transfer the data in Freebase to Wikidata, and in mid-2015 we’ll wind down the Freebase service as a standalone project”.
As well as retiring access for data creation and reading, they are also retiring API access – not good news for those who have built services on top of them. The timetable they shared for the move is as follows:
Before the end of March 2015
– We’ll launch a Wikidata import review tool
– We’ll announce a transition plan for the Freebase Search API & Suggest Widget to a Knowledge Graph-based solution
March 31, 2015
– Freebase as a service will become read-only
– The website will no longer accept edits
– We’ll retire the MQL write API
June 30, 2015
– We’ll retire the Freebase website and APIs
– The last Freebase data dump will remain available, but developers should check out the Wikidata dump
The crystal ball gazers could probably have predicted a move such as this when Google employed, the then lead of Wikidata, Denny Vrandečić a couple of years back. However they could have predicted a load of other outcomes too. 😉
In the long term this should be good news for Wikidata, but in the short term they may have a severe case of indigestion as they attempt to consume data that will, in some estimations, treble the size of Wikidata adding about 40 million Freebase facts into its current 12 million. It won’t be a simple copy job.
Loading Freebase into Wikidata as-is wouldn’t meet the Wikidata community’s guidelines for citation and sourcing of facts — while a significant portion of the facts in Freebase came from Wikipedia itself, those facts were attributed to Wikipedia and not the actual original non-Wikipedia sources. So we’ll be launching a tool for Wikidata community members to match Freebase assertions to potential citations from either Google Search or our Knowledge Vault, so these individual facts can then be properly loaded to Wikidata.
There are obvious murmurings on the community groups about things such as how strict the differing policies for confirming facts are, and how useful the APIs are. There are bound to be some hiccups on this path – more of an arranged marriage than one of love at first sight between the parties.
I have spent many a presentation telling the world how Google have based their Knowledge Graph on the data from Freebase, which they got when acquiring Metaweb in 2010.
So what does this mean for the Knowledge Graph? I believe it is a symptom of the Knowledge Graph coming of age as a core feature of the Google infrastructure. They have used Freebase to seed the Knowledge Graph, but now that seed has grow into a young tree fed by the twin sources of Google search logs, and the rich nutrients delivered by Schema.org structured data embedded in millions of pages on the web. Following the analogy, the seed of Freebase, as a standalone project/brand, just doesn’t fit anymore with the core tree of knowledge that Google is creating and building. No coincidence that they’ll “announce a transition plan for the Freebase Search API & Suggest Widget to a Knowledge Graph-based solution”.
As for Wikidata, if the marriage of data is successful, it will establish it as the source for open structured data on the web and for facts within Wikipedia.
As the live source for information that will often be broader than the Wikipedia it sprang from, I suspect Wikidata’s rise will spur the eventual demise of that other source of structured data from Wikipedia – DBpedia. How in the long term will it be able to compete, as a transformation of occasional dumps of Wikipedia, with a live evolving broader source? Such a demise would be a slow process however – DBpedia has been the de facto link source for such a long time, its URIs are everywhere!
However you see the eventual outcomes for Frebase, Wikidata, and DBpedia, this is big news for structured data on the web.