[Internet World] Intro to the Resource Description Framework (RDF).

I Find Karma (adam@cs.caltech.edu)
Thu, 13 Aug 1998 08:32:16 -0700

Lately I've been trying to learn RDF because DCD is an RDF vocabulary
and I'm trying to learn DCD. Hmmm.

The RDF folkds released a new version of their model and syntax document
on July 20


and the following article from Internet World


is a pretty good introduction to RDF. The author of the article
provided incorrect XML in his example but I think I fixed it below.

At least he got the new XML namespace syntax correct, which the July 20
RDF draft doesn't (because the namespaces draft came out July 31)...

And despite the flood of XML books on the market, Amazon doesn't have
mention of a single RDF book presently available or in the works.
I guess far fewer people will need to know RDF than will need to know

> August 10, 1998
> TECH ABC: The Resource Description Framework
> By James C. Luh
> The Web has grown to millions of hosts, and its content is becoming ever
> richer. But sadly, it's only becoming more and more difficult to make
> sense of that content. The Resource Description Framework (RDF), a
> metadata specification being developed by the World Wide Web Consortium
> (W3C), aims to reverse that trend.
> Though the RDF is still a working draft, many already think it could be
> the most important Internet innovation since the Web itself. As the W3C
> puts it, the RDF could move the Web from being simply machine-readable
> to being machine-understandable.
> The key is metadata. You wouldn't page through every book in a library,
> counting keyword matches to find a book relevant to your search. You
> would most likely consult the library's catalog, an information store
> that describes each library resource in a structured way--such as by
> subject, title, and author.
> In the same way, RDF offers a way to list structured information about a
> Web resource that a program can use to intelligently match results. For
> example, with the right RDF schemas and software in place, a person
> could perform a very specific Web search for biographical information
> about Virginia Woolf, and not be deluged with lists of essays about
> Woolf's work or Web sites about the state of Virginia.
> Searching and cataloging text is just one possible application for RDF.
> RDF is also at the center of two other highly publicized W3C efforts,
> the Platform for Privacy Preferences (P3P) specification for exchanging
> personal information on the Web, and the Platform for Internet Content
> Selection (PICS) specification for content labeling.
> The RDF effort grew out of PICS and was also influenced by the Dublin
> Core Workshop Series, which is focused on defining a metadata vocabulary
> for describing electronic documents.
> Tapping Resources
> RDF identifies objects on the Web as resources (sometimes called
> "nodes"). A resource is anything--from an entire Web page to a snippet
> of XML code--that can be identified with a Uniform Resource Identifier
> (URI).
> RDF lets programmers make statements about those resources. A statement
> asserts a value for a property (sometimes referred to as an "attribute")
> of the resource. Each property is of a specific property type, such as
> "Title" or "Author." For example, consider the statement "The title of
> the document metadata.html is 'Understanding Metadata.'" Expressed in
> terms of the RDF data model, metadata.html is the resource. The property
> type is "Title." The value for the property is "Understanding Metadata."
> The value for a property need not be a simple string of characters. A
> value can be another resource, which in turn can have its own
> properties. For example, we might want to make the statement, "The
> author of the document metadata .html is John Q. Public, whose e-mail
> address is jpublic@iw.com." But there's a problem. John Q. Public can't
> really be the value for a property, because property values can only be
> simple pieces of data or Web resources, and a person qualifies as
> neither. You can get around this by associating John Q. Public with a
> unique URI, such as http:// www.iw.com/staff/jpublic.
> Now you can rephrase the statement for RDF: "The author of the document
> metadata.html is http:// www.iw.com/staff/jpublic. The resource
> http://www.iw.com/staff/jpublic has name John Q. Public and e-mail
> address jpublic@iw.com." RDF statements are encoded in XML. For
> instance, the above example might be encoded as:
> <rdf:RDF xmlns:rdf="http://www.w3.org/TR/WD-rdf-syntax/"
> xmlns:s="http://www.iw.com/OurRDFSchema">
> <rdf:Description about="metadata.html">
> <s:Author resource="http://www.iw.com/staff/jpublic"/>
> </rdf:Description>
> <rdf:Description about="http://www.iw.com/staff/jpublic">
> <s:Name>John Q. Public</s:Name>
> <s:Address>jpublic@iw.com</s:Address>
> </rdf:Description>
> </rdf:RDF>
> The code provides a description of the resource metadata.html, and a
> second description of the resource http://www.iw.com/staff/jpublic.
> RDF syntax also provides other facilities, such as ways to refer to
> containers that hold a number of resources or values, and ways to make
> statements that describe other statements rather than Web resources. All
> of RDF, however, is fundamentally based on the simple model of
> resources, properties, and values.
> A Question of Semantics
> You may have noticed the "s" prefix next to the property types in the
> code above, and the "xmlns" attributes at the start of the code. These
> relate to the problem of differing semantics. Different communities
> attach different semantic meanings to words; for instance, "address"
> could mean anything from a street address to an IP address to a speech
> at Gettysburg. One solution might be to have a central organization
> define what the word "address" means in all contexts.
> RDF takes a different approach; it specifies no particular vocabulary
> and instead lets communities of users define their own vocabularies. An
> RDF description identifies each property type with a prefix (such as "s"
> in the code example), which is in turn mapped to a specific URI using
> the XML namespaces mechanism, which is currently a working draft at the
> W3C.
> The "http://www.iw.com/OurRDFSchema" URI identifies a specific RDF
> schema that contains descriptions of what is meant by various property
> types and specifies rules for properties. For instance, our example
> schema might specify that an author must have one and only one name and
> can have zero or more addresses.
> This decentralized, bottom-up design lets each community define its own
> vocabulary according to its needs. However, it is also one of the major
> obstacles to RDF's promise of universalizing semantics, according to
> Eric Miller, a researcher at the Online Computer Library Center and one
> of the W3C's Model and Syntax chairs. For instance, an online art
> gallery and an online photography archive might benefit from sharing a
> common RDF schema for describing images--but if they establish two
> separate schemas, they could end up being incompatible.
> "The library and museum and architecture and commerce communities will
> all take different approaches to stuff," Miller said. Building consensus
> across all these communities will be a Herculean task, he said--one that
> no one has completely figured out.
> "There isn't a good recipe yet for how to move that type of thing
> forward," Miller said.
> The main contribution of RDF, Miller said, will be to provide a
> groundwork upon which consensus-building efforts can be laid.
> "It's an attempt to sort of standardize the things that can be
> standardized," he said.


In short, computer networks, like the printing press 500 years ago,
allow ordinary citizens to distribute their views in different ways and
to different audiences than were previously possible. This new-found
freedom brings with it many unsolved social, political, and moral
issues. The solution to these problems is left as an exercise for the
-- Andrew S. Tanenbaum, Computer Networks 3rd ed, page 7