There’s nothing premature about publishing government data as Linked Data – it’s happening on a large scale in the UK, US and elsewhere. Where I do agree with Rob (perhaps for the first time ) is that it comes at a cost. However, this isn’t the interesting question, as the same applies to any investment in a nation’s infrastructure. The interesting questions are who bears that cost, and who benefits?

Let’s make a direct comparison between publishing a data set in raw CSV format (probably exported from a database or spreadsheet) and making the extra effort to publish it in RDF according to the Linked Data principles.

Assuming that your spreadsheet doesn’t contain formulas or merged cells that would make the data irregularly shaped, or that you can create a nice database view that denormalises your relational database tables into one, then the cost of publishing data in CSV basically amounts to running the appropriate export of the data and hosting the static file somewhere on the Web. Dead cheap, right?

Oh wait, you’ll need to write some documentation explaining what each of the columns in the CSV file mean, and what types of data people should expect to find in each of these. You’ll also need to create and maintain some kind of directory so people can discover your data in the crazy haystack that is the Web. Not quite so cheap after all.

So what are the comparable processes and costs in the RDF and Linked Data scenario? One option is to use a tool like D2R Server to expose data from your relational database to the Web as RDF, but let’s stick with the CSV example to demonstrate the lo-fi approach.

This is not the place to reproduce an entire guide to publishing Linked Data, but in a nutshell, you’ll need to decide on the format of the URIs you’ll assign to the things described in your data set, select one or more RDF schemata with which to describe your data (analogous to defining what the columns in your CSV file mean and how their contents relate to each other), and then write some code to convert the data in your CSV file to RDF, according to your URI format and the chosen schemata. Last of all, for it to be proper Linked Data, you’ll need to find a related Linked Data set on the Web and create some RDF that links (some of) the things in your data set to things in the other. Just as with conventional Web sites, if people find your data useful or interesting they’ll create some RDF that links the things in their data to the things in yours, gradually creating an unbounded Web of data.

Clearly these extra steps come at a cost compared to publishing raw CSV files. So why bear these costs?

There are two main reasons: discoverability and reusability.

Anyone (deliberately) publishing data on the Web presumably does so because they want other people to be able to find and reuse that data. The beauty of Linked Data is that discoverability is baked in to the combination of RDF and the Linked Data principles. Incoming links to an RDF data set put that data set “into the Web” and outgoing links increase the interconnectivity further.

Yes, you can create an HTML link to a CSV file, but you can’t link to specific things described in the data or say how they relate to each other. Linked Data enables this. Yes, you can publish some documentation alongside a CSV file explaining what each of the columns mean, but that description can’t be interlinked with the data itself, making it self-describing. Linked Data does this. Yes, you can include URIs in the data itself, but CSV provides no mechanism that for indicating that the content of a particular cell is a link to be followed. Linked Data does this. Yes, you can create directories or catalogues that describe the data sets available from a particular publisher, but this doesn’t scale to the Web. Remember what the arrival of Google did to the Yahoo! directory? What we need is a mechanism that supports arbitrary discovery of data sets by bots roaming the Web and building searchable indices of the data they find. Linked Data enables this.

Assuming that a particular data set has been discovered, what is the cost of any one party using that data in a new application? Perhaps this application only needs one data set, in which case all the developer must do is read the documentation to understand the structure of the data and get on with writing code. A much more likely scenario is that the application requires integration of two or more data sets. If each of these data sets is just a CSV file then every application developer must incur the cost of integrating them, i.e. linking together the elements common to both data sets, and must do this for every new data set they want to use in their application. In this scenario the integration cost of using these data sets is proportional to their use. There are no economies of scale. It always costs the same amount, to every consumer.

Not so with Linked Data, which enables the data publisher to identify links between their data and third party data sets, and make these links available to every consumer of that data set by publishing them as RDF along with the data itself. Yes, there is a one-off cost to the publisher in creating the links that are most likely to be useful to data consumers, but that’s a one-off. It doesn’t increase every time a developer uses the data set, and each developer doesn’t have to pay that cost for each data set they use.

If data publishers are seriously interested in promoting the use of their data then this is a cost worth bearing. Why constantly reinvent the wheel by creating new sets of links for every application that uses a certain combination of data sets? Certainly as a UK taxpayer, I would rather the UK Government made this one-off investment in publishing and linking RDF data, thereby lowering the cost for everyone that wanted to use them. This is the way to build a vibrant economy around open data.

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Some background is here:
http://lists.w3.org/Archives/Public/public-lod/2008Apr/0096.html

from    Michael Hausenblas <michael.hausenblas@d...>
to    Ted Thibodeau Jr <tthibodeau@o...>
cc    Kingsley Idehen <kidehen@o...>,Tom Heath <tom.heath@t...>
date    9 February 2009 18:27
subject    Re: "powered by" logos on linkeddata.org MediaWiki

MacTed,

I'll likely not invest time anymore in the Wiki [the MediaWiki instance at community.linkeddata.org - TH]. The plan is to transfer everything to Drupal. We had a lot of hassle with the Wiki configuration and community contribution was rather low. After the spam attack we decided to close it. It only contains few valuable things (glossary and iM maybe) ..

Do you have an account at linkeddata.org Drupal, yet? Otherwise, Tom, would you please be so kind?

Again, sorry for the delay ... it's LDOW-paper-write-up time

Cheers,
Michael


--
Dr. Michael Hausenblas
DERI - Digital Enterprise Research Institute
National University of Ireland, Lower Dangan,
Galway, Ireland, Europe
Tel. +353 91 495730



> From: Ted Thibodeau Jr <tthibodeau@o...>
> Date: Fri, 6 Feb 2009 16:22:31 -0500
> To: Michael Hausenblas <michael.hausenblas@d...>
> Cc: Kingsley Idehen <kidehen@o...>
> Subject: "powered by" logos on linkeddata.org MediaWiki
>
> Hi, Michael --
>
> re: <http://community.linkeddata.org/MediaWiki/index.php?Main_Page>
>
> It appears that the "Powered by Virtuoso" logo that was once alongside
> the
> "Powered by Mediawiki" logo (lower right of every page) has disappeared
> from the main page boilerplate.  Can that get re-added, please?
>
> Please use this logo --
>
>
> <http://boards.openlinksw.com/support/styles/prosilver/theme/images/virt_power
> _no_border.png
>>
>
> -- and make it href link to --
>
>     <http://virtuoso.openlinksw.com/>
>
> Please let me know if there's any difficulty with this.
>
> Thanks,
>
> Ted
>
>
> --
> A: Yes.                      http://www.guckes.net/faq/attribution.html
> | Q: Are you sure?
> | | A: Because it reverses the logical flow of conversation.
> | | | Q: Why is top posting frowned upon?
>
> Ted Thibodeau, Jr.           //               voice +1-781-273-0900 x32
> Evangelism & Support         //        mailto:tthibodeau@o...
> OpenLink Software, Inc.      //              http://www.openlinksw.com/
>                                   http://www.openlinksw.com/weblogs/uda/
> OpenLink Blogs              http://www.openlinksw.com/weblogs/virtuoso/
>                                 http://www.openlinksw.com/blog/~kidehen/
>      Universal Data Access and Virtual Database Technology Providers

from Tom Heath
to Michael Hausenblas
date 9 March 2009 13:49
subject Re: http://linkeddata.org/domains?
mailed-by talisplatform.com

Hey Michael,

Re 2. great! I've created this node
and put it near the top of the primary navigation. You should be able
to write to that at will

Re 1. yes, good idea. I agree we should do this, just need to think
through the IA a little. Can you give me a day or so to chew this
over?

Cheers

Tom.




2009/3/7 Michael Hausenblas :
> Tom,
>
> As you may have gathered we're about to close down the 'old' community Wiki
> [1] and move over to [2]. There is not much active (and valuable) content at
> [1] and we had a lot of troubles with spammer (oh how I hate these ...).
>
> So, basically two things would be great:
>
> 1. I'd like to propose to add a sort of 'domain' or 'community' sub-space,
> such as http://linkeddata.org/domains where I can put our interlinking
> multimedia stuff [3] (and then change the redirect
>
> 2. The second thing would be to find a place at [2] for the glossary [4] -
> seems quite helpful for people.
>
> Any thoughts?
>
>
> Cheers,
> Michael
>
> [1] http://community.linkeddata.org/MediaWiki/index.php?Main_Page
> [2] http://linkeddata.org/
> [3] http://www.interlinkingmultimedia.info/
> [4] http://community.linkeddata.org/MediaWiki/?Glossary
>
> --
> Dr. Michael Hausenblas
> DERI - Digital Enterprise Research Institute
> National University of Ireland, Lower Dangan,
> Galway, Ireland, Europe
> Tel. +353 91 495730
> http://sw-app.org/about.html
> http://webofdata.wordpress.com/

It’s quite hard to follow the indenting in the mail exchange below, so I’ve marked my contributions in bold.


from Tom Heath
to Kingsley Idehen
cc Michael Hausenblas
date 18 June 2009 17:07
subject Re: community.linkeddata.org
mailed-by talisplatform.com

Kingsley,

Also, what news of the previous instance?

Cheers,

Tom.

2009/6/18 Tom Heath :
> Hi Kingsley,
>
> Would the service you envisage at the subdomains you propose provide
> only a URI minting plus FOAF+SSL/OpenID service, or would other stuff
> also be available at that domain? If so, what?
>
> Tom.
>
>

> 2009/6/18 Kingsley Idehen :
>> Tom Heath wrote:
>>>
>>> Hi Kingsley,
>>>
>>> 2009/6/16 Kingsley Idehen :
>>>
>>>>
>>>> Tom Heath wrote:
>>>>
>>>>>
>>>>> Hi Kingsley,
>>>>>
>>>>> 2009/6/16 Kingsley Idehen :
>>>>>
>>>>>
>>>>>>
>>>>>> Tom Heath wrote:
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> Hi Kingsley,
>>>>>>>
>>>>>>> According to our earlier discussions, this subdomain is deprecated in
>>>>>>> favour of the main site at linkeddata.org. If you'd a like a different
>>>>>>> subdomain for specific service just let me know.
>>>>>>>
>>>>>>> Cheers,
>>>>>>>
>>>>>>>
>>>>>>>

>>>>>>
>>>>>> What are the options?
>>>>>>
>>>>>>
>>>>>
>>>>> Guess that depends on the service you have in mind My goal is to
>>>>> avoid fragmentation of the presence at linkeddata.org and subdomains,
>>>>> so favour only creating new subdomains that do something highly
>>>>> specific and do not duplicate functionality or content available
>>>>> elsewhere.
>>>>>
>>>>> Cheers,
>>>>>
>>>>> Tom.
>>>>>
>>>>>
>>>>>

>>>>
>>>> I am not quite understanding you.
>>>>
>>>> What would you see as the scheme for an instance of ODS that gives LOD
>>>> members URIs (of the FOAF+SSL variety)?
>>>>
>>>> Personally, I have no particular interest in pushing this with you per
>>>> se.
>>>> If you somehow deem this unimportant, no problem, I move on etc..
>>>>
>>>
>>> So the proposal is for another equivalent ODS instance, but one that
>>> adds FOAF+SSL support?
>>>
>>> If so, then this does sound important, as FOAF+SSL seems to have lots
>>> to offer. The problem I'm trying to address is as follows: the
>>> feedback I got from people about the previous offering at
>>> community.linkeddata.org was that it was confusing. People didn't
>>> understand what was going on or being offered, and the end result
>>> seemed to be further fragmentation of Linked Data coverage -
>>> particularly problematic for newbies. Therefore a very trimmed down
>>> service offering just personal URIs with FOAF+SSL support would seem
>>> to be of benefit, but I'm not sure of the value of replicating the
>>> previous offering with enhancements.
>>>
>>> Thoughts?
>>>
>>> Incidentally, the previous instance seems to have died. Can it be
>>> reinstated while we finish porting the content across?
>>>
>>> Cheers,
>>>
>>> Tom.
>>>
>>>

>>
>> Tom,
>>
>> Goal is to have a place for people to easily obtain personal URIs. In a way,
>> official LOD community Web IDs.
>> FOAF+SSL is the most important feature here and LOD should be a launch pad.
>>
>> Possible options:
>> yourid.linkeddata.org
>> webid.linkeddata.org
>> me.linkeddata.org
>>
>>
>> This is how it works:
>>
>> 1. New Users open accounts
>> 2. Edit profile
>> 3. Click a button that makes an X.509 certificate, exports to browser, and
>> writes to FOAF space
>> 4. Member visits any FOAF+SSL or OpenID space on the Web and never has to
>> present uid/pwd
>>
>> For existing members, they simply perform steps 3-4.
>>
>>
>> --
>>
>>
>> Regards,
>>
>> Kingsley Idehen Weblog: http://www.openlinksw.com/blog/~kidehen
>> President & CEO OpenLink Software Web: http://www.openlinksw.com
>>
>
> --
> Dr Tom Heath
> Researcher
> Platform Division
> Talis Information Ltd
> T: 0870 400 5000
> W: http://www.talis.com/
>
--
Dr Tom Heath
Researcher
Platform Division
Talis Information Ltd
T: 0870 400 5000
W: http://www.talis.com/


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I may be missing some crucial usage context that reveals the killer characteristics of the iPad, but I’ve tried really hard and still nothing. There are many obvious practical issues with the device:

• it’s too big for a pocket, but not sufficiently more useful than an iPhone or an HTC Hero.
• it’s about the same size as a compact laptop, but with less scope for comfortable rapid input.
• it’s probably too big to cradle comfortably in my hand for prolonged periods, and sitting with one ankle on the other knee is not always practical.

The only scenarios I can conjure up where I could imagine using the device are:

• showing people my holiday photos.
• reviewing design proofs without needing to print them out.

Neither of these, or even both, are very compelling at all. TVs are getting good for viewing photos, by including e.g. an SD card slot, and rumours of the death of paper are greatly exagerated.

Perhaps the most annoying thing about the scenarios used to promote the device is the one about the San Francisco to Tokyo flight, watching video all the way without running out of battery. Any airline with planes worth boarding has personal video screens. I don’t want to bring my own. I’d rather use the space to carry a decent pair of noise-canceling headphones, which I’m sure increase my enjoyment of onboard media far more than a little bit of extra screen real estate. The development I want to see is not a new device that I have to prop on the flimsy airline table, hold tight when we hit some turbulence, and stow away when my food arrives, but the capability to connect my own device to the in-built screen via USB or Bluetooth. Even a bare USB port with power but no connectivity would be a start, allowing me to run low-powered devices (that I already own) during long flights.

OK, so the flight reference is just a touchstone for how long the device can run without mains power, but I think it demonstrates a lack of grounding of the device in realistic scenarios.

Any new device has to have two key characteristics these days for me to get excited: interoperability and convergence. The iPad seems to have very little of either. You could argue that it offers some convergence between smartphones and e-readers, but that’s about as exciting as convergence between a smartphone and a wall clock.

I’m left wondering what the iPad is competing against? I’m guessing it’s paper, whether that’s in the form of a book, brochure, newspaper, restaurant menu or whatever. Unfortunately for Apple, paper is pretty well suited to each of these, especially when you introduce bath water, the risk of theft, or just ketchup, into the equation. Perhaps this is the end of electronic picture frames as dedicated device? Probably about time. Maybe the iPad will make an excellent Spotify console for the living room. Who knows? Whatever happens I can’t see this becoming a mass-market product worthy of even a fraction of the hype.

Where I wish that Apple had expended their creative talent was in addressing the power issue. Not in making sure I could watch 10 hours of back to back video, but in enabling me to spend that energy in whatever way I choose, powering whichever device I choose. It drives me crazy that I carry several batteries around, and short of running my phone off my laptop via USB there is no interoperability between these power sources. If Apple could produce a universal power supply that was sleek, sexy, efficient and interoperable, then I would be interested. Sadly this doesn’t seem to be the way.

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• Tom Heath, John Domingue, and Paul Shabajee (2006) User Interaction and Uptake Challenges to Successfully Deploying Semantic Web Technologies. In Proceedings of The 3rd International Semantic Web User Interaction Workshop (SWUI2006), 5th International Semantic Web Conference (ISWC2006), November 2006, Athens, GA, USA.
• Knud Möller, Tom Heath, Siegfried Handschuh and John Domingue (2007) Recipes for Semantic Web Dog Food – The ESWC and ISWC Metadata Projects. In Proceedings of the 6th International Semantic Web Conference and 2nd Asian Semantic Web Conference (ISWC+ASWC2007), Busan, Korea. LNCS 4825.

Top Five Tips for Semantic Web-enabling a Conference

1. Exploit Existing Workflows

Conferences are incredibly data-rich, but much of this richness is bound up in systems for e.g. paper submission, delegate registration, and scheduling, that aren’t native to the Semantic Web. Recognise this in advance and plan for how you intend to get the data from these systems out into the Web. The good news is that scripts now exists to handle dumps from submission systems such as EasyChair, but you may need to ensure that the conference instance of these systems is configured correctly for your needs. For example, getting dumps from these systems often comes at a price, and if you’re using one instance per track rather than the multi-track options, you may be in for a shock when you ask for the dumps. Speak to the Programme Chairs about this as soon as possible.

In my experience, delegate registration opens months in advance of a conference and often uses a proprietary, one-off system. As early as possible make contact with the person who will be developing and/or running this system, and agree how the registration system can be extended to collect data about the delegates and their affiliations, for example. Obviously there needs to be an opt-in process before this data is published on the public Web.

Collecting these types of data from existing workflows is so monumentally easier than asking people to submit it later through some dedicated means. With this in mind, have modest expectations (in terms of degree of participation) for any system you hope to deploy for people to use before, during and after the conference, whether this is a personalised schedule planner, paper annotation system or rating system for local restaurants. People have massive demands on their time always, and especially at a conference, so any system that isn’t already part of a workflow they are engaged with is likely to get limited uptake.

2. Publish Data Early then Incrementally Improve

Perhaps your goal in publishing RDF data about your conference is simply to do the right thing by eating your own dog food and providing an archival record of the event in machine-readable form. This is fine, but ideally you want people to use the published data before and during the event, not just afterwards. In an ideal world, people will use the data you publish as a foundation for demos of their applications and services and the conference, as means to enhance the event and also to promote their own work. To maximise the chances of this happening you need to make it clear in advance that you will be publishing this data, and give an indication of what the scope of this will be. The RDF available from previous events in the ESWC and ISWC series can give an impression of the shape of the data you will publish (assuming you follow the same modelling patterns), but get samples out early and basic structures in place so people have the chance to prepare. Better to incrementally enhance something than save it all up for a big bang just one week before the conference.

3. Attend to the details

Many of the recent ESWC and ISWC events have done a great job of publishing conference data, and have certainly streamlined the process considerably. However, along the way we’ve lost (or failed to attend to) some of the small but significant facts that relate to a conference, such as the location, venue, sponsors and keynote speakers. This stuff matters, and is the kind of data that probably doesn’t get recorded elsewhere. Obviously publishing data about the conference papers is important, but from an archival point of view this information is at least recorded by the publishers of the proceedings. The more tacit, historical knowledge about a conference series may be of great interest in the future, but is at risk of slipping away.

4. Piggy-back on Existing Infrastructure

As I discovered while coordinating the Semantic Web Technologies for ESWC2006, deploying event-specific services is simply making a rod for your own back. Who is going to ensure these stay alive after the event is over and everyone moves onto the next thing? The answer is probably no-one. The domain-registration will lapse, the server will get hacked or develop a fault, the person who once knew why that site mattered will take a job elsewhere, and the data will disappear in the process. Therefore it’s critical that every event uses infrastructure that is already embedded in everyday usage and also/therefore has a future. The best example of this is data.semanticweb.org, the de facto home for Linked Data from Web-related events. This service has support from SWSA, and enough buy-in from the community, to minimise the risk that it will ever go away. By all means host the data on the conference Web site if you must, but don’t dream of not mirroring it at data.semanticweb.org, with owl:sameAs links to equivalent URIs in that namespace for all entities in your data set.

5. Put Your Data in the Web

Remember that while putting your data on the Web for others to use is a great start, it’s going to be of greatest use to people if it’s also *in* the Web. This is a frequently overlooked distinction, but it really matters. No one in their right mind would dream of having a Web site with no incoming or outgoing links, and the same applies to data. Wherever possible the entities in your data set need to be linked to related entities in other data sets. This could be as simple as linking the conference venue to the town in which it is located, where the URI for the town comes from Geonames. Linking in this way ensures that consumers of the data can discover related information, and avoids you having to publish redundant information that already exists somewhere else on the Web. The really great news is that data.semanticweb.org already provides URIs for many people who have published in the Semantic Web field, and (aside from some complexities with special characters in names) linking to these really can be achieved in one line of code. When it’s this easy there really are no excuses.

Conclusions

Reading the above points back before I hit publish, I realise they focus on Semantic Web-enabling the conference as a whole, rather than specifically the conference Web site, which was the focus of Chris’s original question. I think we know a decent amount about publishing Linked Data on the Web, so hopefully these tips usefully address the more process-oriented than technical aspects.

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Getting a piece of the action I have no objection to per se. This was exactly my aim with chiip.co.uk my (currently somewhat on ice) shop window to Amazon – visitors could find products via search engines and, if desired, buy them through a trusted supplier, earning me enough commission on the side to pay my hosting bill for a month or two. The difference here is that I just tweaked the site layout to show off the content to search engines in its best light. I never polluted anyone else’s space to gain exposure. People that do this are getting me down.

Revyu has become somewhat popular as a target, presumably due to its decent ranking in the search engines. The site didn’t gain this position through spamming other sites with backlinks, but by having some simple principles baked into the site design from the start. They’re the same basic principles I’ve used on any site I’ve created, and have generally served me well. A few years ago I wrote down the principles that guide me, and I share this first draft here as a service to people who want to optimise the exposure of their site and still be able to sleep at night.

Before you read the tips though bear this in mind: there is something of an art to this, but it isn’t rocket science, and it certainly isn’t black magic. If you can create a Web site then you can optimise pretty well for search engines without paying a single self-appointed “expert” a single penny. This is bread and butter stuff. These approaches should be part of the core skill set of any Web developer rather than an afterthought addressed through some external process. The tips below are not guaranteed to work and may become defunct at any time (some may be defunct already – does anyone ever use frames these days?). However, follow these and you’ll be 80% of the way there.

Search Engine Optimisation Tips

1. there’s only so much you can do, and this may change at any time
2. don’t try and trick the search engines, just be honest
3. use web standards and clean code
4. use css for styling and layout
5. put important text first in the page; let this influence your design, it’s probably what users want too, especially if they’re on non-standard browsers
6. choose page titles carefully
7. use meta tags, but only if they’re accurate
8. use robot meta tags, and robots.txt
9. use structural markup, especially headings
10. give anchors sensible text (“click here” does not qualify as sensible)
11. use link titles and alt text
12. give files and folders meaningful names
13. provide default pages in directories so people can hack your URLs
14. forge meaningful (human) links with other sites, and make technical links accordingly
15. encourage inward links to your site
    • make urls readable and linkable to
    • don’t break links (at least give redirects)
16. don’t use javascript for links/popup windows that you want to be indexed
17. avoid links embedded in flash movies
18. never use frames
19. never use cookies to power navigation
20. give example searches or browse trees to open databases to search engines
21. maximise the content richness of pages
22. avoid leaf node pages (always create links back to the rest of the site)
23. limit the use of PDFs
24. take common typos into account, or spelling variations (optimisation vs optimization is a good example)
25. update the site regularly
26. don’t use hidden text or comments to try and convey spam words
27. don’t embed text in images
28. avoid writing out text using javascript
29. don’t use browser detection to alter content or restrict access
30. provide meaningful error pages
31. be realistic about what you can achieve optimsation-wise
32. establish a traffic baseline
33. use monitoring tools to track your progress

At some point I hope to provide evidence backing up each of these claims. In the meantime you’ll just have to trust me, but it won’t cost you anything.

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With this in mind Leigh Dodds, Jordan Hatcher, Kaitlin Thaney and I submitted a tutorial proposal to this years International Semantic Web Conference addressing exactly these kind of issues. The good news is that our proposal has been accepted, and therefore there will be a half day tutorial on “Legal and Social Frameworks for Sharing Data on the Web” at ISWC2009 in Washington DC in October (more details online soon). With Jordan present to provide the legal perspective there’ll finally be someone taking part in the discussion who can’t prefix their statements with “I’m not a lawyer, but…”

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The layer cake diagram is probably one of the most used and abused images associated with the Semantic Web vision. In the diagram, each technology or concept in the Semantic Web stack is a layer, with Crypto providing some kind of irregular icing down one side. I’d like to propose a different interpretation of the Semantic Web as a cake.

In my view, the technologies aren’t layers in the finished cake, they’re the raw ingredients that must be mixed and baked to make the cake that is the Semantic Web itself. URIs are the grains of flour; an ingredient that is essential but by itself rather bland, and lacking form and coherence. RDF triples are the egg that can bind together this URI flour. This cake is taking shape, but it’s lacking flavour. In the Semantic Web cake these flavourings, such as FOAF, SIOC, or the Programmes Ontology, are concocted on a base of RDFS and OWL. Simple cakes based on one or two flavours can be very tasty, but for our Semantic Web cake to be truly delicious we want a wide range of flavours, with some dominating others in different parts of the cake.

Once we’ve baked our cake, by putting our RDF data online according to the Linked Data principles, we’ll probably want to decorate it. Perhaps some icing or cherries on top, in the form of inferred RDF triples, would make it even more delicious. With such an appealing data cake it’s inevitable that people will want to consume it, but we have to make sure that everyone can have a slice rather than letting a big data gluton run off with the cake and deprive everyone else of this treat. We need some sort of knife; preferably one like SPARQL, that allows people to help themselves to the parts of the cake they like best. Will the cake baked and decorated, and will all the tools in place, it’s time to invite some friends round (maybe even some agents) and start consuming.

(I see that Jim Hendler’s keynote at ESWC2009 will talk about the layer cake; I’m intrigued to see how he choses to serve up the analogy).

Related posts:

1. Putting a Conference into the Semantic Web Chris Gutteridge asked this question about semantically enabling conference Web...

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People learning about Linked Data frequently ask “what’s the relationship between Linked Data and the Semantic Web?”, which is a fair and good question. One of the responses that crops up relatively frequently is that Linked Data is just an attempt to rebrand the Semantic Web. In my experience these kind of rebranding comments come mostly from people who have a certain impression of the Semantic Web vision (which may or may not be accurate), don’t like this vision, and therefore dismiss Linked Data on this basis without actually considering what it means (i.e. a means to dismantle data silos), and without necessarily rethinking their original view of the Semantic Web concept. I prefer to see it this way…

Think about HTML documents; when people started weaving these together with hyperlinks we got a Web of documents. Now think about data. When people started weaving individual bits of data together with RDF triples (that expressed the relationship between these bits of data) we saw the emergence of a Web of data. Linked Data is no more complex than this – connecting related data across the Web using URIs, HTTP and RDF. Of course there are many ways to have linked data, but in common usage Linked Data refers to the principles set out by Tim Berners-Lee in 2006.

So if we link data together using Web technologies, and according to these principles, the result is a Web of data. Personally I use the term Web of data largely interchangeably with the term Semantic Web, although not everyone in the Semantic Web world would agree with this. The precise term I use depends on the audience. With Semantic Web geeks I say Semantic Web, with others I tend to say Web of data – it’s not about rebranding, it’s about using terms that make sense to your audience, and Web of data speaks to people much more clearly than Semantic Web. Similarly, Linked Data isn’t about rebranding the Semantic Web, it’s about clarifying its fundamentals.

Tim Berners-Lee said several times last year, in public, that “Linked Data is the Semantic Web done right” (e.g. see these slides from Linked Data Planet in New York), and who am I to argue, it’s his vision. But to see this as a recent trend or a u-turn ignores the historical context. On page 191 of my copy of Weaving the Web (dated 2000, ISBN-13: 9781587990182) it says:

The first step is putting data on the Web in a form that machines can naturally understand, or converting it to that form. This creates what I call a Semantic Web – a web of data that can be processed directly or indirectly by machines.

I’m not sure this quote adequately captures the importance of links in the whole picture, but no one can claim that the Web of data label is recent marketing spin invented to make the Semantic Web palatable. This was always the deal. It’s certainly how I understood the concept (and what inspired me to do a PhD in the area).

If others  have somehow diverted the Semantic Web vision down some side road since Weaving the Web was written, then that’s unfortunate. (In my experience the Linking Open Data project was an attempt to reconnect the Semantic Web community with the some of the key aspects of the original vision that were being overlooked, like having a real Web of data as the basis for research). I certainly notice plenty of unjustified attempts at present to co-opt the term Semantic Web, now that it’s no longer a dirty word, and drive it off down some dodgy alleyway. Some of these products, services or companies may be applications or services that use some semantic technology and are delivered over the Web, but that doesn’t make them Semantic Web applications, services or companies. Anything claiming the Semantic Web label needs to get its hands dirty with Linked Data somewhere along the way. That’s just how it is.

So to return to Tim O’Reilly’s tweet, he’s not far wrong about the lack of difference between Linked Data, Semantic Web and RDF (we’ll ignore the means vs end vs technology distinction), but I’d love to know who he’s quoting about the explicit rebranding.

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Today I had the dubious privilege of being branded a snake oil salesman, on the grounds that my “boosting” of the Semantic Web isn’t backed up by adequate eating of my own Semantic Web dog food. Apparently neither my publications page, or any of my other pages on my site, have any “intelligent content tagging”, whatever that is (I assume this means RDFa).

If it does mean RDFa, then true, but this does completely overlook the RDF/XML on my site, which as a whole is built according to Linked Data principles. More galling is that the claim completely overlooks the work I’ve done in the Semantic Web community that kick-started a lot of the ongoing dog food activity at ESWC and ISWC  (this was not a lone effort by any means: Knud Moeller, Sean Bechhofer, Chris Bizer, Richard Cyganiak and many, many others deserve as much or more credit as I do for ensuring it continued, as will Michael Hausenblas and Harith Alani at ESWC2009). Just to rub salt into the wound, these inaccuracies are being propagated across the Web in other people’s blog comments, e.g. here.

I’d like to end with some insightful meta analysis or reflection on this, but unfortunately I need to get ready for a trip to the US to run a workshop on Visual Interfaces to the Social and Semantic Web and give two days worth of Linked Data tutorials. Hope I don’t get stopped at US customs with that consignment of snake oil So, no great insights for now, just a copy of my response in case it ever disappears from the original site in a puff of smoke.

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Seth,

I would be the first to agree with you that the Semantic Web community has not always eaten its own dogfood to the extent that it should have. It was for exactly this reason that in 2006 I produced RDF descriptions of almost all aspects of the European Semantic Web Conference (http://www.eswc2006.org/rdf/) and coordinated the deployment of numerous Semantic Web technologies at the conference (http://www.eswc2006.org/technologies/). My aim was to learn about deploying these technologies in the wild, and feed back my findings (positive or negative) to the community. The results of my evaluation were published here: http://swui.semanticweb.org/swui06/papers/Heath/Heath.pdf

Regarding the production of RDF to describe Semantic Web conferences, there had been some small efforts in this direction at previous events, but nothing comprehensive. ESWC2006 changed that for good, and there have been RDF descriptions of all European and International Semantic Web conferences published ever since. This data has been published using an ontology that derives largely from the one I created for ESWC2006, with significant contributions along the way from others. There is now a regular position on the organising committee of these conferences for people charged with coordinating this effort for the event. Knud Moeller and I shared this role at ISWC2007, where we also reported back to the community on our efforts up to that point: http://iswc2007.semanticweb.org/papers/795.pdf. Many other people have contributed significantly along the way, and this combined effort has produced the repository of data at http://data.semanticweb.org/ to which RDF descriptions of ESWC2009 will also be added.

But as you point out, the institutions that promote the Semantic Web also need to put their money where their mouth is. Agreed. While I was a PhD student at The Open University’s Knowledge Media Institute, I argued for developer time to add RDF descriptions about all KMi members to the institute’s People pages (http://kmi.open.ac.uk/people/), and tutored the developers in how to apply their existing Web development skills to exposing Semantic Markup.

My PhD work included development of the reviewing and rating site Revyu.com (http://revyu.com/), which won first prize in the 2007 Semantic Web Challenge. I can’t speak for the judges, but my hunch is that a major factor in Revyu’s success in the Challenge stemmed from its strict adherence to the Linked Data principles (http://www.w3.org/DesignIssues/LinkedData.html), which have done so much to help people make the Semantic Web a reality. Revyu publishes human-readable (i.e. HTML) and machine-readable (i.e. RDF) content side by side, but humans won’t see this RDF (I assume this is what you mean by “intelligent content tagging”) unless they know where to look; this is the intended behaviour, and works according to the techniques described in the How to Publish Linked Data on the Web tutorial (http://linkeddata.org/docs/how-to-publish) that I co-authored with Chris Bizer and Richard Cyganiak.

My personal Web site follows the same principles and uses the same techniques. If you view the source of my homepage you will see a link tag in the header that looks like this:
&lt;link rel=”meta” type=”application/rdf+xml” title=”RDF” href=”http://tomheath.com/home/rdf” /&gt;
This is the link that tells Semantic Web crawlers to look elsewhere for the semantic markup on my site, not in the human-readable HTML page where it might get broken if I tweak the layout. If we ever meet in person I will give you one of my business cards, which doesn’t give the address of my homepage – it gives my Web URI (http://tomheath.com/id/me); humans and machines can look up this URI and retrieve information about me in a form that suits them (i.e. HTML or RDF), and follow links in that HTML or RDF to other related information. In the words of Tim Berners-Lee, this setup is “the Semantic Web done right, and the Web done right”.

Yes, it’s unfortunate that my publications page doesn’t have an RDF equivalent; perhaps I’ve been too busy investing time and energy in initiatives that will have an impact beyond the scope of my own Web site? But either way, your comment that “nor any of his other pages (that I saw) uses any form of intelligent content tagging” just doesn’t stack up. Before you make these sorts of claims I would ask, reasonably and politely, that you show due diligence in looking thoroughly, and in the right places, for the semantic markup on my site. For anyone who is in any doubt that it’s there, click on the small “RDF META” tile on the right hand side of pages on my site.

I think it’s also reasonable to expect, if you’re truly interested in how the Semantic Web community is tackling this issue, that I might be given the chance to respond to your queries in advance of this article going out, as Adrian Paschke and Alexander Wahler were. I can only hope that this response helps provide a fuller picture of the situation, with respect to my efforts and those of the community at large.

Lastly, a technical point. We need to remember that the Semantic Web allows anyone to say anything, anywhere (I’m borrowing from Dean Allemang and Jim Hendler here). So, while RDF data about my publications may not be available on my own site yet, you can find pieces of the jigsaw at data.semanticweb.org, and if all conferences and journals published their proceedings/tables of contents in RDF, then my job would simply be to join the pieces together, and I wouldn’t be faced with manually updating my list of publications. OK, so we’re not there quite yet. Yes, there’s work to be done, but we’re trying.

Tom.
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