Semantic Web tutorial
This tutorial, the first of a three-part series, introduces SPARQL - a query language and data access protocol for the Semantic Web. SPARQL is defined in terms of the W3C's RDF data model and will work for any data source that can be mapped into RDF. The specification is under development by the RDF Data Access Working Group (DAWG) and has recently reached Last Call Working Draft.
At this point in its life cycle the specification is stable enough that developers can begin seriously exploring its capabilities. And the availability of several SPARQL query engines means that this exploration can be practical rather than theoretical.
But what if you're a lot more interested in Web 2.0, which is practical and real, than in the Semantic Web, about which opinions vary widely? Why might you want to go to the trouble of learning SPARQL? For dyed-in-the-wool Semantic Web fans, this question may well be a no-brainer: RDF has needed a standard query language for some time and having one will make many development tasks much easier.
However SPARQL has a much wider potential audience. A key aspect of the Web 2.0 idea is the ability to extract and query information held across many different ad hoc, third-party apps, services, or repositories. That ability to move in and among various data sources is key to the Web 2.0 idea of the mashup - take a little Google Maps, salt with some eBay, and sprinkle with a heaping hunk of Flickr, right?
SPARQL, which is both a query language and a data access protocol, has the ability to become a key component in Web 2.0 applications: as a standard backed by a flexible data model, it can provide a common query mechanism for all Web 2.0 applications. XML.com managing editor Kendall Clark has published an excellent essay (Web 2.0 Meet The Semantic Web) that expands more fully on this idea. SPARQL should be of interest to developers exploring the available options for publishing open data on the Web.
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