Older blog entries for mhausenblas (starting at number 23)

Less than a year ago I asked W3C’s Technical Architecture Group (TAG) essentially if

… the [image] representation derived via [content negotiation from a generic resource] is equivalent to the RDF [served from it]

I asked for a “a note, a specification, etc. that normatively defines what equivalency really is”.

So, after some back and forth between the TAG and the IETF HTTPbis Working Group I happened to receive an answer. Thanks to all involved, I guess it was worth waiting. Seems like the upcoming HTTPbis standard will address this issue, essentially stating that

… in all cases, the supplier of representations has the responsibility for determining which representations might be considered to be the “same information”.

As an aside: I guess I’ll have to be patient again – this time I asked the above mentioned HTTPbis WG why the caching heuristics exclude the 303 header (see the current draft of HTTP/1.1, part 6: Caching, section 2.3.1.1.). But it’s not even two weeks into the question, so I don’t recon I’ll get mail from the chaps before 01/2011

Filed under: FYI, IETF, Linked Data, W3C

Yesterday we had our first DERI-internal RDFa hands-on workshop. More than 20 colleagues attended, equipped with their laptop and a RDFa cheat sheet we provided. The goal was to support people in manually marking up their Web pages with RDFa, contributing to the growing Web of Data.

We plan to hold this workshop every two weeks, so in case you’re around, come and join us!

Posted in Linked Data

Our eldest one is turning seven soon and for him it is hard to imagine the pre-Web area. Sometimes he asks me but how did you do this or that without the Web? and quite often I must admit I don’t know the answer. Maybe some of the things we do nowadays were simply non-actions some 20y ago, like updating Twitter

Anyway, let’s remind ourselves that the essential idea of the Web was doing ‘Hypertext over the Internet’, and TimBL was not the only one who had this idea. However, as far I can tell he was the only one who was successful on a large scale with sustainable and tangible outcome.

One thing that bothers me is that we are mentally still subscribed to the document-centric point-of-view. And, as a result, an application-centric point of view. What do I mean by that? Well, imagine a piece of paper and a pen. I can virtually do any kind of illustration and notes on it. I don’t need to get another pen to create a table; I don’t need a second sort of paper to draw a picture, etc.

And yet, we’re still used to think along this line. If you don’t believe me: even the latest, coolest Web application suites, such as GDocs essentially forces you to decide up-front, which kind of document you wanna create. Shouldn’t we have overcome this?

The good news is: we’re now able to overcome the document-centric POV, due to what Linked Data enables. I won’t focus on the technical details or their evolution for now but on what I call result-centric. This essentially means that one is interested in the result of an action rather than by the means it has been achieved. A little analogy might help: say, you want to travel from Galway to Madrid and the only requirement is that it has to be as cheap as possible (hey, I’m a researcher – time doesn’t matter, but budget constraints). So, what counts at the end of the day is that (i) you arrive in Madrid and (ii) you’ve spent as little money as possible. This might mean you have to switch from plane to bus to train, maybe, but anyway, the result matters to you, not which kind of transport medium you’ve used. Same with certain, if not all kinds of tasks on the computer. Frankly, I don’t give a damn if I have to use this or that application. I might just need to write a report, including figures and tables and the more efficient I can do this, the better. Today, this likely means I’ve got to use some two or three applications (which I have to know, to pay for, etc. – yey, TCO do matter).

Coming back to Linked Data, which essentially enables ubiquitous and seamless data integration, one can imagine a new class of application: general purpose viewing and editing – a truly result-centric way of working with the computer. In fact, the first generation of the ‘read-only’ case, Linked Data browser, such as DIG’s Tabulator, OpenLink’s Data Explorer or Sigma are available already.

What we now need, I think, is DDE/OLE done right. On the Web. Based on Linked Data. Addressing security, trust, privacy and billing issues. Allowing us to move forward. From document-centric to result-centric.

As an aside: this post was influenced by a book I’m currently reading.

Posted in Linked Data

I’m just about to release a new version of the voiD editor, called ve2. It’s currently located at http://ld2sd.deri.org/ve2/ (note that this is a temporary location; I gotta find some time setting up our new LiDRC lab environment).

Anyway, the point is really: every now and then one deploys a Web application (such as ve2; see, that’s why I needed the pitch) and likely wants to also tell the world out there a bit about the application. Some things you want to share with the Web at large that come immediately to mind are:

• who created the app and who maintains it (creator, legal entity, etc.)
• which software it has been created with (Java, PHP, jQuery, etc.)
• where the source code of the app is
• on which other services it depends on (such as Google calendar, flickr API, DBpedia lookup, etc.)
• acknowledgments
• usage conditions

Now, for most of the stuff one can of course use DOAP, the Description of a Project vocabulary, as we did (using RDFa) in the riese project, but some of the metadata goes beyond this, in my experience.

To save myself time (and hopefully you as well) I thought it might not hurt to put together an RDFa template for precisely this job: Announcing Application Metadata on the Web of Data . So, I put my initial proposal, based on Dublin Core and DOAP, at:

http://lab.linkeddata.deri.ie/2010/res/web-app-metadata-template.html

Note: The WebApp metadata template is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License. You may want to include a reference to this blog post.

Posted in Idea, Linked Data, Proposal

Though Linked Data (the set of principles) can be considered being around since roughly three years, the technologies it builds upon are around already considerable longer: two of the three core Linked Data technologies (URIs and HTTP) are some 20y old. And because I know that you’re at least as curious as I am ;) I thought it might be nice to sit down and capture a more complete picture:

So, why a thermo-view? Well, actually using technologies is a bit like ice-skating, isn’t it? As long as a technology is still evolving, it is sort of fluid (like water). Then there are crystallisation point(s), the technology matures and can be used (a thin layer of ice). After a while, the technology is established and robust – able to carry heavy load (a thick layer of ice).

Lesson learned: it takes time and the right environmental conditions for a technology to mature. Can you take this into account, please, the next time you’re tempted to ask: “when will the Semantic Web arrive?” :D

So much for the past 10 years.

What’s upcoming, you might wonder? Well we hear what the “Web 3.0 leaders” say and here is what I think will happen:

• In 2010 we will continue to witness how Linked Data is successfully applied in the Governmental domain (in the UK, in the US, for transparency etc.) and in the Enterprise area (eCommerce: GoodRelations, IBM, etc.).
• In 2011, Linked Data tools and libraries will be ubiquitous. A developer will use Linked Open Data (LOD) in her application just as she would do with her local RDBMS (actually, there are libraries already emerging that allow you to do this).
• In 2012 there will be thousands of LOD datasets available. Issues around provenance and dataset dynamics have been resolved.
• In 2013, Linked Data-based solutions have displaced heavy-weight and costly SOA solutions in the Enterprises.
• From 2014 on, Linked Data is taught in elementary schools. Game Over.

Ok, admittedly, the last bullet point is likely to be taken with a grain of salt ;)

However, I’d love to hear what you think. What are your predictions – factual or fiction, both welcome – for Linked Data? Where do you see the biggest potential for Linked Data and its applications in the near and not-so-near-future?

One of the often overlooked, IMO yet important features of RESTful applications is “hypermedia as the engine of application state” (or HATEOS as RESTafarians prefer it ;) – Roy commented on this issue a while ago:

When representations are provided in hypertext form with typed relations (using microformats of HTML, RDF in N3 or XML, or even SVG), then automated agents can traverse these applications almost as well as any human. There are plenty of examples in the linked data communities. More important to me is that the same design reflects good human-Web design, and thus we can design the protocols to support both machine and human-driven applications by following the same architectural style.

As far as I can tell, most people get the stuff (more or less) right concerning nouns (resources, URIs) and verbs (HTTP methods such as GET, POST, etc.) but neglect the HATEOS part. I’m not sure why this is so, but for a start let’s have a look at available formats:

• Most obviously one can use HTML with its official link types or with microformats (for historic reasons see also a proposal for a wider spectrum of link types and for ongoing discussions you might want to keep an eye on the @rel attribute discussion).
• Many people use Atom (concerning RDF, see also the interesting discussion via Ed Summer’s blog)
• There are a few non-standard, in-house solutions (for example the one discussed in an InfoQ article)

Summing up, one could understand that there is a need for a standard format that allows to represent typed links in an extensible way and is able to serve humans and machines. In 2008 I argued that RDFa is very well suited for Linked Data and now I’m about to extend this slightly: one very good way to realise HATEOS is indeed RDFa.

Happy to hear your thoughts about this (admittedly bold) statement!

Update: for the dataset dynamics demo developed during the Linked Data Camp Vienna there is now also a screen-cast available (video, slides in PDF):

Jürgen Umbrich and I virtually participated in the LDC09 session regarding datasets dynamics.

Over the past couple of days, we hacked a little demo on a distributed change notification system for Linked Open Data, based on voiD+dady and (a slightly modified version ) of an Atom feed. Here is the overall setup:

In case you want to play around with it yourself, you can check out the source code as well. Feedback and feature requests welcome ;)

I recently wrote about caching support in the Linked Open Data here and got nice feedback (and questions ;) from dataset publisher. In a follow-up mail exchange, Mark Nottingham was to kind to provide me with two very valuable resources I’d like to share with you:

• The Resource Expert Droid (redbot), http://redbot.org/, a tool that ‘checks HTTP resources to see how they’ll behave, pointing out common problems and suggesting improvements’, especially useful if you want to debug Linked Data sets on the HTTP level.
• Concerning the question how my findings relate to the Web at a large, Mark pointed out a community project, called Web Authoring Statistics, which performed an analysis on quite a few Web documents, yielding results about various document-related but also HTTP-related stuff.

Please let me know if you are aware of more resources in this area (studies, etc.) and I’ll post it here!

So, the other day I had a look at caching support in the Linked Open Data cloud and it turns out that there is a related discussion regarding caching on the ietf-http-wg@w3.org mailing list.

Then, there is another related update from Bill Roberts: Delivering Linked Data quickly with which I wholeheartedly agree.

To take the entire stuff a step further I tried to outline the overall problem in a short slide deck (best viewed full-screen ;)

My hunch is that 80% of the stuff is already out there available (such as Atom, Changeset vocabulary, voiD, etc.) and only minor pieces are missing. Next step would be to hammer out a simple demo and gather some more experiences with it. In case you are interested to chime in let me know :)