Can Atom be considered Linked Data?

There has been a lot of community discussion in the past few months about the scope of Linked Data and whether it is just limited to RDF. Paul Miller asked Does Linked Data need RDF? and opened an intense debate.

Recently Ed Summers posted this example of a SKOS concept modelled in Atom

Can this be considered Linked Data? Is it just a serialisation of RDF (RDF/Atom perhaps) and sits alongside RDF/XML, Turtle, RDF/JSON and NTriples? When people say Linked Data is RDF do they mean RDF the model or RDF the syntax?

Let's assume that beside the need of URIs, to be linked data you need a way to decompose it to triples, well, to map it to the RDF abstract syntax (you don't actually need a particular serialisation to manifest somewhere in the process).

Then I would say that if the transformation to RDF is not explicitly defined, it is not linked data, as you need to "sniff" the content and "know" how to transform/extract it.

But, once somebody puts a GRDDL "hint" in the Atom namespace document, all the atom feeds would become automatically linked data, right?

To answer the question, a particular Atom document is not linked data if there is explicitly defined mapping/transformation to RDF (in the document itself or in the namespace document); but if Atom becomes an agreed/standardised (controlled?) serialisation, then it would became linked data as the mapping to the RDF's abstract syntax would be "known".

Then I would push your question to even web pages with microformats (a html page with RDFa is linked data already, I hope) — if you have the proper html @profile defined, that means that you can follow links towards how to GRDDL the data? is it linked-data?

I would say yes. As long that you can follow an explicitly defined trail towards the data embedded there (via its extraction service).

Then what is not linked data? well, when you have to guess it, to use heuristic methods to "extract" it, that would not be linked data.

Twilight zone: a web page with a link rel="alternate" type="application/rdf+xml" towards its equivalent data, is it linked data? I would say not quite, as it points to a different document and since they were separated at birth, they may evolve independently.

Considering that there is no "RDF the syntax" (there's RDF/XML, n3/turtle, RDFa, SPARQL query results format...) I consider Linked Data as RDF to refer to the data model, i.e. a series of machine-readable triples that each consist of the identification of a resource and a property name/value pair about that resource. With its clear identification of bits of metadata about specific resources, treating an Atom file as a series of triples is pretty easy, and I know I've seen code to convert it somewhere, so I'd consider it to qualify as linked data.

This raises its head again with ...

Atom can be parsed into triples, and it can link to URIs that dereference to more data from other places on the web.

But, if you are serious about publishing "linked data", about interoperability, about data becoming exponentially more useful the more it is connected with other data, I doubt you would choose Atom as your sole means of publishing that data, because the majority of RDF tools won't work with it.

In fact, it seems few people who are serious about "linked data" in any quantity, rest easy until they have provided 3 or 4 different serialisations of their data.

If the Atom uses universal identifiers in common with other sites, then yes. Otherwise no.

Rule of thumb: If it's linked to other bits of data (via URIs), it's linked data, otherwise it's just data.

Did someone have a look at Atom+RDF? It seems to make use of GRDDL, but I am sure the ontology might be used for putting the SemanticOverflow Atom data into a RDF repository with SPARQL end point...

Datalinkyness comes in degrees; the more we make it sound like an all-or-nothing affair, the sillier we sound to the outside world.

Let's ask more practical questions: eg. If I publish my SQL database using Atom, is it hard to consume with RDF tools, mix with other RDF data and query with SPARQL? what's the best RDF/Atom combination these days? (Atom-OWL? Yahoo DataRSS? Something with GRDDL? does GRDDL get much real world use? when is it considered secure, is GRDDL much used with XSLT2, XQuery? etc ...?)