One could argue that these examples, while not being RDF, still
adhere to the RDF abstract syntax (triples describing typed directed
relationships between resource).
> Here's the first way (plain 'ol JSON object):
>
> {
> "id": "http://example.com/people/luca";,
> "type": "http://schema.org/Person";,
> "name": "Luca Matteis"
> }
>
> The document above is interpreted as Linked Data using the following
> rules:
>
> 1. The thing you're talking about is identified via 'id'.
> 2. The type of the thing you're talking about is identified via 'type'.
> 3. All keys, except for 'id' and 'type', are appended to 'type''s value,
> with a '/' separator.
>
> That's Linked Data. It has no formal relationship to RDF.
The three rules could be seen as a simple GRDDL-like specification.
Applying them will give you a subset of RDF (no blank nodes?).
> Here's the second way (Microdata):
>
> http://www.w3.org/TR/microdata/
>
> The base Microdata spec has nothing to do with RDF. However, if you are
> going to assert that RDFa is Linked Data, then you have to assert that
> Microdata is Linked Data. Since Microdata has no linkage to RDF, what
> are you left with? Answer: A syntax that allows you to express Linked
> Data without using RDF in any way.
I'll skip this since other people know the fine points of Microdata
much better than me.
> Here's the third way (RFC-5988: Web Linking):
>
> http://tools.ietf.org/html/rfc5988
>
> The Web Linking RFC defines a typed connection between two resources that
> are identified by Internationalised Resource Identifiers (IRIs) and is
> comprised of:
>
> o A context IRI,
> o a link relation type (Section 4),
> o a target IRI, and
> o optionally, target attributes.
>
> Isn't this Linked Data as well?
Yes, and I see the same concept as in RDF - resources and typed links,
all denoted by URIs.
> Here's a fourth way (HAL - Hypertext Application Language):
>
> http://stateless.co/hal_specification.html
>
> """
> HAL provides a set of conventions for expressing hyperlinks to, and
> embeddedness of, related resources - the rest of a HAL document is just
> plain old JSON or XML. Instead of using linkless JSON/XML, or spending
> time developing a custom media type, you can just use HAL and focus on
> defining and documenting the link relations that direct your clients
> through your API. HAL is a bit like HTML for machines, in that it is
> generic and designed to drive many different types of application.
> """
>
> HAL is also Linked Data.
As above.
> To assert that Linked Data requires RDF requires you to make compelling
> arguments against at least these four pieces of evidence.
Perhaps I'm moving the goal posts here, but my take on this is that in
order to achive the goals of Linked Data you will end up with something
that overlaps the RDF abstract model. Most cases seem to subsets - no
blank nodes or typed literals &c. The interesting question is the semantics.
An useful baseline for the LD community could be that all Linked Data
follows the RDF sematics[] unless other semantics are explicitly
specified.
Tore Eriksson
[] http://www.w3.org/TR/rdf-mt/
