Geospatial Semantic Web Blog

In my previous post, I wrote about Metalink, a new markup language and technology for unifying Internet download. The current Metalink language is defined in XML. Publishers use this language to describe meta-data about their download files on the Web.

Today Anthony Bryan email me an interesting example that maps an existing Metalink description into RDF and uses SPARQL to query this description. In his message, Anthony didn’t mention the author of this example. But I suspect it’s the creation of Dan Brickley (since couple URL points to spypixel.com) — maybe Dan had blogged about this before, but I missed his post.

Here is how the example goes.

1. Given a Metalink file (e.g., OpenOffice Metalink), use some transformation technology (e.g., XSLT) to map the XML content into RDF — here is an RDF document output.
2. To check if this RDF document is well-formed, use the W3C RDF validator.
3. Let’s assume that this document and many others similar documents are stored in a Metalink directory server or in Swoogle. We can build applications to query those servers for Metalink data.
4. Here is a SPARQL SELECT that generates information about different OpenOffice download URL and their respective downloading preference score (see also a PDF screenshot of the output result).

This is what we can learn from the above exercise.

First, XML and RDF will and should co-exist on the Web. New technologies like Metalink will continue to embrace XML as the core language for publishing information on the Web. My philosophy always: If a problem can be adequately solved by XML, we shouldn’t force it to be solved by RDF.

Second, RDF will complement XML as a standard technology for supporting knowledge sharing and semantic queries on the Web. I believe RDF-based query language such SPARQL will be more effective and flexible than XML-based query language such as XPath/XQuery for finding and discovering knowledge on the Web.

Lastly, a wider adoption of Semantic Web technology will depend on our ability to bridge gaps between research and real-world applications. Proof-of-concept examples (e.g., the one in the above) that build on real-world applications (e.g., Metalink) can inspire people who are not already in the Semantic Web circle to pick up the idea of the Semantic Web, and go wild with it.