Thank you to everyone who took the time to share a wide range of views in response to yesterday’s post in its comments, on Twitter, and out on your own blogs. Although reduced to silence throughout the day because of other commitments, I have been reading and learning from all of you. And, despite the sometimes intemperate language of my original post, your contributions have all been thoughtful, measured, and informative.

Several comments raised the duality of RDF; RDF the model and RDF the format (which can itself be expressed in more forms than the RDF/XML of which most might think). Kingsley’s right, of course, when he asks;

“Is RDF a Data Model or a Format re this discussion. The answer to this question is of utmost importance re coherence.”

Honestly, I’m not sure that I know which it was meant to be… but I can fairly safely suggest that the concerns I expressed become increasingly pronounced as we move from ‘model’ toward ‘format.’ I’m still worried about insisting upon the RDF model in anything other than its loosest sense, but can at least see a glimmer of justification for doing so… whereas insisting upon the format seems several steps too far.

I also liked the simplicity with which Alan Dix and Elliot Smith responded to Rob Styles’ ‘Paul Miller is right… and so is Ian Davis,’ writing;

“Surely the critical issue is whether the semantics are available, not whether they are in RDF. If a csv file is published AND suitable semantics are available, then you know which columns are URIs or whatever else.”

and

“if you publish data on the web and a suitable semantics for interpreting that data and linking it to other data, then why isn’t it Linked Data? It just so happens that RDF has a clear(er) semantics describing the interpretation of its data elements (URIs in particular) than a spreadsheet does; it doesn’t mean you couldn’t apply similar semantics to a spreadsheet if you were so inclined.”

Indeed.

Although I actually agree with every single word, Justin Leavesley‘s comment possibly gets close to the nub of things;

“Yes the same mistake was made with the rise of the web.

Once you had URIs and HTTP you already had plain text which is a perfectly good way to encode content. By adopting the STANDARD convention of HTML, all sort of existing text based formats with their various mark ups were locked out. That locked out a lot of content that already existed and required anyone who wanted to play to convert existing content into a html format.

Of course it did have the small side effect that to consume web content you only needed a browser that understood one convention i.e. html.

The same is true of RDF. XML is the equivalent of ascii in this regard. Sure it is a good way to write down data, but it isn’t sufficient to actually use that data unless you understand the various special conventions.

RDF gives you a standard way to understand TYPES of data that you have never seen before. You simply cannot do that with XML alone. You must build a convention at a different level from syntax, which can be expressed as XML. We have, its called RDF!

Ask yourself the question. Why hasn’t the linking of data taken off before? If there is all this data out there, why didn’t it just get linked together?

Because linking between different conventions isn’t very useful.

The problem has never been the linking of data, that is easy as soon as you have URIs. It is meaningfully linking different data so that you have something useful not just a mess. This itself then pulls in more data. Just as we have seen with the growth of the web and just as we are now seeing with the growth of ‘linked data’”

There are surely far more failed attempts to prematurely constrain in the name of ‘standardisation’ than successful ones. If we’re trying to grow and nurture a market (in more senses than just the commercial,) shouldn’t we be more permissive? I’d far rather be engaged in ‘selling’ (to maintain the market metaphor) the benefits of RDF than apologising for its imposition, wouldn’t you?

RDF (definitely the syntax, possibly the model) is a point in time solution to a set of problems that we collectively consider worthy of resolution. The problems will still be there — and hopefully still worthy of resolution — long after the next technical solution has come along.

A lot of the comments, too, talk about ‘converting’ to RDF. Toby, for example, writes;

“Linked data certainly needs to be *linked*, and after that, it’s pretty important to describe the relationship that each link between resources represents (i.e. “this is a link to a parent resource”, “this is link to a resource that represents a place nearby to this place”).

Once you have that, the idea of a triple emerges almost by itself, and what you have is suddenly starting to look very much like RDF. If your format is not RDF, then it’s likely to be convertable to RDF fairly trivially.”

Yes… but if, for the sake of argument, I happen to have ‘the idea of a triple’ in some other form, I may not want or need to convert. RDF is a solution, not the end-goal.

Alan Morrison says something similar, again assuming (?) RDF to be something more than it necessarily is;

“The RDF family provides a metadata umbrella that non-RDF can fit under. It’s possible to avoid religious arguments by allowing alternatives as long as they can be converted to fit under the umbrella.”

Finally, for now, Bruce D’Arcus writes,

“The microdata in HTML5 discussions suggests to me that the first thing that goes out the window when you accept RDF as optional (or more typically, a more pejorative unneeded overkill) is ironically the feature most important to both RDF and linked data: the URI (microdata allows one to use string or reverse DNS identifiers instead for property names and types).”

I’d like to learn more about that, and understand the forces at play there…

And after all the comment and discussion… I’m still convinced that RDF’s model and format are important and useful, and still convinced that they should not be mandatory for Linked Data. Mandatory for ‘Linked Data in RDF,’ yes. Mandatory for ‘Linked Data,’ no.

Before going any further, let’s get a few things crystal clear;

1. The recent success of the Linked Data meme is long overdue, very welcome, and entirely capable of carrying the Web of Data far beyond its current niche adherents. A lot of my current work involves arguing that more organisations should adopt this approach;
2. The Resource Description Framework, RDF, is a key — and powerful — piece in W3C‘s Semantic Web Architecture. Since its earliest days, I have played various parts in advocating the potential of RDF and will continue to do so;
3. RDF is an obvious means of publishing — and consuming — Linked Data powerfully, flexibly, and interoperably. I will continue to argue this, and to advocate its wider adoption.

So far, so good.

The problem, I contend, comes when well-meaning and knowledgeable advocates of both Linked Data and RDF conflate the two and infer, imply or assert that ‘Linked Data’ can only be Linked Data if expressed in RDF.

This dogmatism makes me deeply uncomfortable, and I find myself unable to agree with the underlying premise.

The rest of this post attempts to explain why, hopefully more lucidly than I or those with whom I was debating managed on Friday evening via the largely unsuitable medium of the 140 character tweet.

Andy Powell started things off lucidly enough on Friday, asking;

“is there an agreed name for an approach that adopts the 4 principles of #linkeddata minus the phrase, ‘using the standards (RDF, SPARQL)’ ??”

I was amongst those to respond, suggesting as I usually do that;

“well, personally, I’d argue that Linked Data does NOT require that phrase. But I know others disagree…  ”

Other pieces of that conversation can be extracted from the stream; start by scrolling to the bottom, find Andy’s tweet, and work back toward the top.

It’s worth noting that two of those arguing most vehemently against me were former colleagues Ian Davis and Leigh Dodds. I have massive respect for the technical prowess of both (which is certainly greater than my own), and have learned a great deal from Ian in particular over the years that we have known one another. This issue, though, is one on which we have long disagreed, and it was interesting to see the subject of many a difference of opinion in the bars of various conference hotels spill into this public arena.

Anyway, now let me try to explain what I meant.

Perhaps the most commonly cited definition for Linked Data is the one to which Andy was referring; Sir Tim Berners-Lee‘s Linked Data – Design Issues document. It’s worth noting that this document is clearly flagged (in the current version amended on 18 June 2009, at least) as being both a ‘personal view only’ and ‘imperfect but published.’ So a very long way from being a ‘standard,’ ‘specification,’ or ‘definition,’ but certainly still a pretty good starting point, and one to which I often direct clients and others.

Berners-Lee begins,

“The Semantic Web isn’t just about putting data on the web. It is about making links, so that a person or machine can explore the web of data.  With linked data, when you have some of it, you can find other, related, data.”

(my emphasis)

That sounds good, doesn’t it? Indeed, we talked about that on the Linked Data panel I moderated at the recent Semantic Technology Conference, and I’ve embedded the video here.

It is the next section of Berners-Lee’s document that is used to validate the view that Linked Data needs RDF;

“1. Use URIs as names for things

2. Use HTTP URIs so that people can look up those names

3. When someone looks up a URI, provide useful information, using the standards (RDF, SPARQL)

4. Include links to other URIs. so that they can discover more things.

(my emphasis)”

On one reading, an unambiguous validation of the view with which I disagree. On another, a suggestion of best practice, expressed as part of a ‘personal view’ with which we are perfectly entitled to take issue.

Would the zealots be calmed by the simple insertion of ‘preferably’ or ‘ideally,’ immediately after point three’s second comma? Maybe. Or perhaps the fires of Linked Data’s self-appointed Inquisition would be stoked for Berners-Lee himself.

Talk of Linked Data, Open Data, the Web of Data and related concepts in recent years have led to a quite remarkable shift in attitude amongst individuals, public bodies and private corporations. Almost everywhere my work takes me, clever people are seriously grappling with the implications of consuming from or contributing to these emerging ecosystems. Not all of their questions have good answers, and not all of the technological, strategic and business implications have necessarily been fully worked through. But these people are asking the questions, and they are asking them in all seriousness.That is a dramatic and welcome shift.

Some, such as the BBC, Thomson Reuters and the UK Government’s Central Office of Information are sufficiently persuaded of the benefits to take risks and to open the previously closed in taking a lead. Others will follow, as fears are assuaged, doubts eased, and benefits realised.

Despite this undoubted progress, the green shoots of a Linked Data ecology remain delicate. By moving from a message that stresses the value of unambiguous and web-addressable naming (HTTP URIs), providing ‘useful information,’ and enabling people to ‘discover more things’ by linking toward a message that elevates one of the best mechanisms (RDF) for achieving this to become the only permissible approach, we do the broader aims great harm.

Yes, those already in the club will probably be very pleased with the purity and functionality of the toys in their playground. But they will have barred a far larger group with data to share, a willingness to learn, and an enthusiasm to engage. At best, they will have slowed the growth of the pool of Linked Data quite dramatically. At worst, they will have created an increasingly irrelevant backwater that more pragmatic people will simply route around. Perhaps, in their pragmatism, those people will now never look seriously at RDF and its power, scared away by the fervour of those who sought to elevate it too high, and too fast.

What are we after? More Linked Data, or more RDF? I sincerely hope it’s the former.

So let’s see loads more Linked Data, and plenty of evangelism as to why RDF could be the best way to do it. But let’s not ostracise the vast majority of potential participants, contributors and beneficiaries in the world of Linked Data, just because they haven’t wholeheartedly embraced RDF yet.

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