But even when logical alone is useful, many important problems are not tractable.

See for example my post:
Formal definitions are less useful than you think
http://www.daniel-lemire.com/blog/archives/2007/12/05/formal-definitions-are-less-useful-than-you-think/

Can ontologies be useful? Yes, but on a very limited scale. For small problems involving few people and easy inferences.

For large-scale difficult problems involving large enterprises, then ontologies are almost certainly not worth it.

You will need to extend your idea of semantics so that it goes beyond ontologies. You almost surely need to rely on statistical methods, machine learning, and so on.

Particularly the ability to reason about an endpoint without having to expressly code that reasoning into the way applications interact.

I see the semantic layer as the ultimate loose coupling driving heterogenous data sources.

I’m quite interested in you view point on this.

No URI will ever be the Eiffel tower!

Most of the most useful applications of Semantic Web technologies I’ve seen only deal with a simple data model – analogeous to relational databases, but more compatible with the Web.

How so?

But although you can build any kind of an application as a one-off, if you use Semantic Web standards they are compatible in a way that we’re not seeing from other approaches (…)

As far as I can tell, this is an unsupported claim.

Semantic Web technologies do allow you to make statements like “this carrot is yellow”, but my point was that it isn’t necessary to have deep philosophy for it to be useful. Most of the most useful applications of Semantic Web technologies I’ve seen only deal with a simple data model – analogeous to relational databases, but more compatible with the Web.

“I see no application there that could not have been built equally well without the Semantic Web” – sure, to a great extent this is true (quite a range of applications are easier to build using RDF tools, but this isn’t the significant part). But although you can build any kind of an application as a one-off, if you use Semantic Web standards they are compatible in a way that we’re not seeing from other approaches (mashups are fine, but they don’t have the flexibility the use of a common language can provide).

Let’s see if one link will get past the spam trap : an 8 minute video, The Semantic Web of Data.

Semantic Web technologies make this infrastructure more useful.

I see no evidence that the Semantic Web makes the Web more useful.

Semantics on the Web definitively makes the Web more useful (take RSS feeds as an example!)

If I can say “the Eiffel Tower landmark in Paris”, why shouldn’t I give a URI to that concept and say things about that concept?

Of course you can give it a URI. Here is the one I would use:

http://en.wikipedia.org/wiki/Eiffel_tower

That does not prove that the Semantic Web is useful or well-founded, only that wikipedia is a cool thing.

It’s possible to apply mathematical reasoning to problems like “if I have two carrots and add two more, how many will I have?”. The true philosophical meaning of ‘carrot’ is orthogonal. Same goes for the logic used in Semantic Web systems (and virtually all computer programming).

Google is already able to answer this one. Try typing “2+2″.

If you do no need to know what a carrot is, whether it is white or yellow, then we are not talking about “Semantic Web”.

As for the Semantic Web applications you point to… I did not say there were none strictly speaking, but I see no application there that could not have been built equally well without the Semantic Web. In other words, the Semantic Web community has not provided any proof or any evidence that it is making the Web better.

There is ample evidence that common file formats are insanely useful. Microsoft Word comes to mind. RSS/Atom also.

Does RDF make common format easier to design? Does RDF make common format automagical?

Where is your evidence that RDF is so potent?

If anything, on the topic of common file formats, it seems that XML was the major contribution as of late. RDF is not.

In fact, there is evidence that RDF is a bad idea. Look at RSS 1.0 which is an instance of RDF… look at what a disaster it has been!

Disclaimer: I do teach RDF to my student, if only for historical reasons. I do not think that RDF is bad. But RDF has not served us well.

Saying “the semantic web will fail” is limited, as you mean the aspect of “computer will understand automatically”. Biased, I would be very happy if I could move my social network and pictures away from flickr to another site without loss of information, but thanks to walled gardens and web 2.0 business, this is not possible out-of-the-box. With semantic web, at least the data formats would be the same.

Taking your main points with that in mind:

“1) it relies, at best, on an incomplete theory of meaning”

- the Semantic Web relies on existing human approaches to naming and describing things, with conventions and mathematical formalisation here and there to help with computer representation. Existing human systems operate without a complete theory of meaning. There is nothing to suggest that a complete theory of meaning is a prerequisite of useful Web systems (and quite a lot to suggest the opposite).

“2) unlike what is suggested by the Semantic Web, meanings are not fixed and are tied to contexts.”

If I can say “the Eiffel Tower landmark in Paris”, why shouldn’t I give a URI to that concept and say things about that concept?

You say: “The fact that the Semantic Web claims to be able to represent, at least simple things, without ambiguity is akin to proposing a new language which itself without ambiguity”. This is missing a layer of indirection. The things that are represented are generally human concepts. What is said about relations between those identified concepts *may* be unambiguous in a mathematical sense. The concept itself is largely a human definition, though things can be done to help disambiguate matters: e.g. “the tower in this photograph”.

It’s possible to apply mathematical reasoning to problems like “if I have two carrots and add two more, how many will I have?”. The true philosophical meaning of ‘carrot’ is orthogonal. Same goes for the logic used in Semantic Web systems (and virtually all computer programming).

Re. “People always refer, vaguely, to applications of the Semantic Web, but they rarely point to any in particular.”.

Maybe people assume other people know how to use a search engine. Try googling “* is a semantic web application”.

Here are a few of my favourites:

DBPedia and the Linking Open Data cloud:
http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData

Sweet Tools is the nicest list I know of (hmm, host seems to be having trouble today):
http://www.mkbergman.com/?page_id=325

You can find more at:
http://esw.w3.org/topic/

and:
http://blogs.talis.com/nodalities/this_weeks_semantic_web/

I am very sympathetic to a pragmatic approach in Information Technology. Irrespective of their flaws, Semantic Web technologies could prove useful. But they have not proved useful, and yet, we have been funding them for nearly ten years. People always refer, vaguely, to applications of the Semantic Web, but they rarely point to any in particular.

Arguably, it may take another 20 years for the Semantic Web to grow useful. Who knows?