RE: ISSUE-66: LinkedDataT

On 5 Aug 2014 at 11:07, Ruben Verborgh wrote:
> Jumping in, as this is very relevant for the Linked Data Fragments spec
[1].
> In fact, this issue appearing after I drafted an introductory section
called
>     "What Linked Data is"
> might not be a coincidence. (And it's very good timing in any case.)

Yeah, this is mostly about the Linked Data Fragments spec.


> Let me start out by saying I was totally oblivious of "non-RDF Linked
Data".
> I.e., I had always assumed that Linked Data is in RDF;
> probably because Tim's original principles explicitly mention this [2].

Funny fact: the "original principles" didn't explicitly mention it:

 
https://web.archive.org/web/20061115043657/http://www.w3.org/DesignIssues/Li
nkedData.html

It took 3 years till that was added.


> Then again, we all know the principles are quite vague:
> - RDF* and SPARQL are mentioned between parentheses.
>   Did this mean "e.g., RDF*, SPARQL", or "i.e., RDF*, SPARQL"?
>   That's an important difference, and we'll likely never know.
> - Where is the asterisk after RDF ever resolved?
> Maybe I just missed the majority of the discussion;
> i.e., posts like [3] were written in 2009.
> 
> That said, me being in the community for 4 years
> and never having heard about (or being selectively deaf towards)
> non-RDF Linked Data, means something at least.

We had a very long (and heated) discussion about this when we standardized
JSON-LD. It starts more or less here

 
http://lists.w3.org/Archives/Public/public-rdf-comments/2013Jun/thread.html#
msg28

in case you want to waste a couple of hours (days?) reading more about this
:-)


> I'd dare to say that the majority of people do assume
> that Linked Data is just done with RDF.

That's obviously true for the Semantic Web community. Not so true for the
rest of the world :-) Hydra tries to bridge the gap between those two worlds
(just as JSON-LD does).


> So to what extent is it then necessary to clarify this?

I think it is very important as our group is not a homogenous group of
Semantic Web experts.


>>> i was specifically trying not to get that discussion going. just asking

I'd also like to urge to not get into that discussion.


>>> whether there should be some definition/clarification of the term, just
>>> to let readers know what it means in the context of the spec/community.
>>> if you define a broad term to mean a narrow thing, then this might be
>>> helpful to avoid possible confusion.

In my opinion we should define it. At the moment, I think it is clear that
LDF are *exclusively* for RDF. It would be interesting to see if it can be
generalize in the future but till we get to that point I think we should
simply be honest about it.


> What do you think about the current introduction
> to the triple pattern fragments spec [1]?

It's quite nice but I think it could be further improved, especially for
people without a lot of SemWeb background. 


> Not knowing about this issue yet, I phrased it as:
> 
>     By publishing Linked Data [LINKED-DATA],
>     we enable automated clients to consume information.

Hmm... automated clients such as Google are quite happy consuming plain old
HTML... I know what you are trying to say but people who haven't spent a
whole lot of time on this won't understand it, I think.


>     In practice, this information is available as RDF triples [.]
>
> So it leaves the question open whether non-RDF Linked Data exists;
> it just says that, in practice, it will be RDF. Good enough?

Maybe it would be more straightforward to explain it the other way round:
  - documents are in natural language
  - machines are bad in understanding natural language
  - machines prefer structured data using unambiguous identifiers
  - the Web uses URLs* as identifiers
  - RDF allows data to be expressed in a machine-processable way by
leveraging URLs
  (- RDF expresses data in the form of triples) -- could be omitted
  - RDF can be serialized in various formats such as JSON-LD, HTML+RDFa, or
Turtle

* I think simply talking about URLs instead of URI or IRI is fine in this
case

I would also suggest to use a different term than "Linked Data document". Is
it actually needed or could we also get rid of this concept?


>> I think a definition could help.  I suggest copying the one from the
>> W3C Linked Data Glossary verbatim (and referencing that document),
>> rather than trying to craft a new one and risking another long debate
about
>> what it should be.
> 
> Sadly, I think that definition is quite complicated.
> Here it is at full length, copied from [4]:
> 
>     Linked Data
>     
>     A pattern for hyperlinking machine-readable data sets to each other
>     using Semantic Web techniques, especially via the use of RDF and URIs.
>     Enables distributed SPARQL queries of the data sets and a browsing
>     or discovery approach to finding information (as compared to a search
strategy).
>     Linked Data is intended for access by both humans and machines.
>     Linked Data uses the RDF family of standards for data interchange
>     (e.g., RDF/XML, RDFa, Turtle) and query (SPARQL).
>     If Linked Data is published on the public Web,
>     it is generally called Linked Open Data. See also [Linked Data
Principles].
>
> It forces you to understand:
> - Semantic Web
> - RDF
> - URIs
> - SPARQL
> to make sense out of it.

I fully agree. This definition is not going to help anyone.


> On the technical level, nothing prohibits us from making Linked Data
> Fragments broader than RDF. We'd have to be very careful, however,
> that the concept would still be sufficiently meaningful; that it
> doesn't become hollow by broadening it.

Yeah, I would like to explore that in the future. However, till we get
there, we should make it clear that at least a mapping to RDF is required.


Cheers,
Markus


> [1] http://www.hydra-cg.com/spec/latest/linked-data-fragments/
> [2] http://www.w3.org/DesignIssues/LinkedData.html
> [3] http://cloudofdata.com/2009/07/does-linked-data-need-rdf/
> [4] http://www.w3.org/TR/ld-glossary/#linked-data


--
Markus Lanthaler
@markuslanthaler

Received on Tuesday, 5 August 2014 11:45:04 UTC