Overview of RDF and SPARQL

Overview of RDF and SPARQL

RDF (Resource Description Framework)

A format for exchanging data on the Web, usually implemented in XML. RDF is used to create machine-readable descriptions of resources available on the Internet. RDF descriptions contain metadata, such as the author or creation date of a webpage, the topic of an article, or who is allowed to use a resource.

The Resource Description Framework (RDF) is a W3C standard format for storing arbitrary data on the Web and elsewhere (http://w3c.org/RDF/). It's particularly good for storing metadata about files and other machine-accessible resources. You can store handfuls of RDF inside the resources they describe, outside of them, in relational databases, in XML, or any place you like, and then easily combine these handfuls into a database that you can use for queries, reports, and graphs. (Patel-Schneider, 2009)

The ability to exchange and combine RDF from different places across the Web has made it a cornerstone of the W3C's "Semantic Web" plans, and it's already proving itself helpful in accomplishing much more mundane tasks. Whether your data is structured or unstructured, typed or untyped, centralized or distributed, RDF just may make the job of storing and using that data easier. (Corby, 2010)

DF's ability to assign any predicate/object pair to any subject makes it an ideal format for a freeform database. For example, if my address book lists each person's name, address, phone number, and e-mail address, and I want to add a single new field for one person, it's just one more triple to add, with no schema revision to contend with. (The W3C does have a specification for RDF schema available, but RDF schemas are more commonly used to provide additional information about data, such as data types and domains, than to constrain the entered data.) If I add a triple saying that Nick Charles has a dogName value of "Asta," then displaying Nick's information shows the dog's name along with Nick's address and other information, even if no one else in my address book ever had a dogName property assigned.

This is one reason that the Open Source Applications Foundation's Chandler personal information manager project (http:// www.osafoundation.org/our_product_desc .htm) uses RDF as a native format to store data. It's also the key difference between RSS 1.0 and its competitors: Because of its RDF basis, adding new classes of data to a given RSS 1.0 item doesn't require an extension to the RSS specification-the use of RDF builds extensibility right in.

The flexibility of RDF storage also makes it popular for adding metadata to disk files that don't have an obvious slot for metadata, especially if you need to aggregate this data into collections. With your files as subjects, think of the predicate/object pairs as being like javadoc doc tags, except that you can make up your own tags and use them for any kind of file, Java source, or otherwise.

RDF triple

RDF gives you a machine-readable way to say anything about anything. The basic data structure upon which everything else is built is called a "triple," and is described using rather grammatical terminology: (subject, predicate, ...