2008-06-18
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RDF is becoming part of the data store for many applications today—it provides a means of modeling data in an easily understood manner.
There are as many ways to model data as there are developers with better ideas after getting frustrated using some current technology. The idea of turning a real world object into data that represents the object and then modeling that data into an abstraction of the original is hard for most people to understand, much less visualize. Resource Description Framework (RDF) is another in a long series of data modeling techniques, but this one is different from most. An RDF model relies on a triple that consists of a subject, predicate, and object. For example, in the sentence, “An apple has the color red.” the subject is “An apple,” the predicate is “has the color,” and the object is “red.” Most people can understand this model because it expresses the abstract concept in terms that humans easily comprehend. Unlike most Web technologies, RDF examines the relationship between things (not objects)—A is a part of B.
This is the first a two-part series. In this first part, you’ll discover why RDF is becoming popular and how it contributes toward a new method of distributing data called the Semantic Web. Both RDF and the Semantic Web are World Wide Web Consortium (W3C) standards. You can view them at http://www.w3.org/RDF/ and http://www.w3.org/2001/sw/.
RDF Exposed
RDF reminds me of that game Othello—minutes to learn, a lifetime to master. The concept of the RDF triple is easy to understand, but thinking about how one thing relates to another isn’t always that simple. Saying A is a part of B seems simple until you begin to use it to model real world data. Some developers will find RDF difficult to use because it seemingly breaks all of the rules that they’re accustomed to. Even so, the RDF technique of modeling provides a method of defining relationships in a way that people can understand and it works well for modeling data that doesn’t necessarily fit well into standard modeling strategies. You can currently find RDF used to model these kinds of data:
· Really Simple Syndication (RSS): Access to information such as articles (http://www.rssboard.org/rss-specification)
· Friend of a Friend (FOAF): Access to information about people and their relationships (http://
· Description of a Career (DOAC): Information about someone’s career, whatever that career includes (http://ramonantonio.net/doac/0.1/)
· Description of a Project (DOAP): A method of describing open source projects (http://trac.usefulinc.com/doap)
You can find many other uses of RDF on the Internet today. In addition, you can use RDF to build a model of any other data you like. Later in this article, you’ll see how to build a simple contact data model and create a data file using it. The one overriding consideration about RDF is that it expresses the relationship between things in some way.
Because of the current uses of RDF, it’s easy to think that RDF probably builds on
Considering the Semantic Web
One of the most interesting uses of RDF is the semantic Web, which is best described as a web of data. The idea behind the semantic Web is being able to see data in context with other data. One of the examples I’ve seen used is being able to look in your calendar application and see the checks you wrote on that day, even though the calendar application and accounting program are completely separate.
The semantic Web relies on RDF and other standards to provide a common format for all data and to relate that data to the real world object it represents. This focus differs from the original intent of the Internet, which was to exchange documents. By creating a connection between data and the real world object it represents, someone can begin in one database and move to another based solely on the kind of real world object they want to discuss. You can read more about the semantic Web at http://www.w3.org/2001/sw/.
The important issue to consider for this article is that LINQ, combined with RDF, gives you a window into the semantic Web. Consider the kind of data you see in the sections that follow as a starting point to a much larger world. Once you understand the concepts behind RDF, you can use it to begin working with the semantic Web in detail. Of course, every trip begins with a first step and that’s the purpose of this article—to help you take that first step into a much larger world of data modeling.
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