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RDF and OWL Are W3C Recommendations
J1 writes "The World Wide Web Consortium today released the Resource Description Framework (RDF) and the OWL Web Ontology Language (OWL) as W3C Recommendations. RDF is used to represent information and to exchange knowledge in the Web. OWL is used to publish and share sets of terms called ontologies, supporting advanced Web search, software agents and knowledge management. Read the press release for the full list of twelve documents, read the testimonials, and visit the Semantic Web home page."
...you might be interested in a new project hosting site which was just opened - SemWebCentral. It already hosts several DAML tools, including ObjectViewer, the beginnings of an OWL plugin for Eclipse, and various others.
Shirky's peice on the Semantic Web is far below his normal quality. It's poorly researched and poorly considered. (Speaking as someone misquoted in the article...)
For good responses see Peter Van Dijck or Paul Ford.
RDF is actually quite usefull and is used when making extensions for FireFox/Mozilla among other things. Be sure to check out the RDF validator here as it can save you time.
It will be very interesting to see how RDF/XUL stands up against XAML.
Go here for teh [sic] funny.
ALT tags are for the most part used for screen readers. Unnecessary images, used just to enhance the look of the page are often given alt="" values so that the screen reader will skip the image entirely (ie: read nothing instead of saying "image foo.jpg is here with no alt tag").
A lot of RDF out there is in FOAF and RSS 1.0 vocabularies. Increasingly, people use to link RDF files, which makes it possible to have RDF crawlers ("scutters") harvest RDF from the web. I have an RDF aggregator service running that crawls the semantic web. There's a lot of useless broken RDF out there, so if you put RDF on your web site please use W3C's RDF Validator to check for valid RDF.
Okay, I thought those were relatively pleasant reads, which can be a plus. (And I wanted to say something fast, before slashdot buried any response I might make...)
My actual response at the time is brief and chatty. The response from Dan Brickley is also short and sweet. Neither of us felt it was worth the time to reply point-by-point.
The "misquoting" is to suggest that my "how you buy a book on the Semantic Web" sketch should possibly cause Jeff Bezos to lose sleep. I was trying to explain an experimental protocol in a way I hoped my grandmother could understand (seriously!) and Shirky thinks I'm sketching out Amazon's doom? I don't expect the Semantic Web to doom anyone but folks who want to keep data exchange laborious.
The OWL sense of "ontology" is the second sense, if you read "theory" in the formal (computer science/mathematical logic) sense.
That is, an OWL ontology tells readers (especially computers) what kinds of things exist and what kinds of relationships they can have to each other.
Some of the OWL specs are actually pretty readable. Try starting with the OWL Overview. (Others, like OWL Semantics, are... more challenging.)
An Ontology is supposed to tell you what things are (what things there are) and how those things are related.
OWL and RDF schemas are ontologies in the philosophical sense in that they define a set of entities and relations which allow you to make meaningful inferences from assertions framed in terms defined by the ontologies in question. An Ontology defines the categories and relations that make up a world.
Ontologies are not themselves information (except in the trivial sense) but rather structures which allow agents (human or machine) to make sense of information.
To use an extremely basic example, let's say you have an Ontology for all things connected to selling snacks, you would have categories for Snacks, Owners, Currency and Transactions. Each of those categories might have sub categories (Snacks:hot,Snacks:cold) and each Category will have constraints on the relationships it can have. You would also have entries for the relations that can exist (Whole-part, owns, consumes). As you can see even a very basic ontology quickly grows to be quite complex.