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.

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Dave asked if he can use the same URI for both his FOAF profile and OpenID HTML page. I thought I had to use RDFa or Microformats to solve the problem. But then, a quick Google search I found a simple solution from RDF in HTML.

I added few FOAF statements about myself in my OpenID HTML page. It passed W3C RDF validator test, and I can successfully sign on to livejournal.com.

Do you know other approaches that will enable the use of one single URI for both FOAF profile and OpenID HTML page?

In the blogosphere, there are ping services like Ping-o-Matic and technorati ping for notifying search engines about blog updates. Ping services are extremely useful. They made easy for search engines to discover new blogs and their changes. Also, they helped individual blog owners to spread information and attract more readers.

As the Semantic Web grows, we also need similar services. Ping.SemanticWeb.Org is an experimental service for notifying search engines (or semantic web bots) about changes made in semantic web documents.

The present service accepts pings from semantic web documents that describe SIOC, FOAF and DOAP. SIOC is an ontology for describing discussion forums and posts in online community sites. FOAF is an ontology for describing people and their social network relations. DOAP is an ontology for describing open source projects on the Web.

The Semantic Web ping services are interesting for the following reasons.

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UMBC Ebiquity Group reports how W3C geo vocabulary is currently used in semantic web documents. The analysis is done using the statistics compiled by Swoogle — a Semantic Web search engine and crawler. Swoogle currently knows about 500,000 semantic web documents and 300,000,000 RDF triples.

Some interesting facts from the report:

• Geo is currently the 10th highest ranked vocabulary according to Swoogle’s ontology ranking algorithm
• About 240,000 documents reference geo’s namespace
• Top used namespace abbreviation for this ontology is “geo”, “pos” and “wgs84_pos”
• Instances of geo:Point appear far more often in the range value of foaf:base_near property than all other referenced properties combined (close to 100,000 : 1).
• Property geo:long (longitude) and geo:lat (latitude) are often used by instances of geo:Point. Other instances that use these two properties include instances of the Airport class from airport-ont, geo:SpatialThing, dc:image, rdfs:Resource, foaf:Image, and foaf:Person. (see the full list for geo:long and the full list for geo:lat).
• Property geo:alt (altitude) is not used very often in comparison to geo:long and geo:lat.

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