What's so special about RDF?http://en.wikipedia.org/wiki/Resource_Description_Framework
Hierarchical vs. Relational DatabasesBack when dinosaurs, err, IBM Mainframes ruled the land, everyone used hierarchical databases (if they used a database that is). IMS is the most well known. http://en.wikipedia.org/wiki/Information_Management_System
The reason relational databases, and SQL in particular, have succeeded in spite of the "complexity" (compared to storing the data in a way that conveniently matches the application's model) is because of what happens when applications change and when the need to reuse and repurpose the data arises. RDF schemas have that same relationship with XML schemas. RDF represents the data as n-tuples which are very much like rows in a relational database. That requires the same sort of normalization that is needed for relational database modeling, rather than encouraging the willy-nilly hierarchical models supported by XML Schema, and is thus responsible for the "complexity" that has garnered the scorn of so many XML hackers, err architects, who "just want to get the job done".
That mindset is what led to RDF being dropped in RSS 2.0 and Atom. RSS actually stands for RDF Site Summary (RSS 1.0), not Really Simple Syndication (RSS 2.0 & Atom).
But what happens when application designs change? And what about reusing and repurposing the data? These are things in great demand in the Web by users. And while Open Source Software development puts the developer's interests at the pinnacle, working and playing well with others can be just as valuable (or maybe even more so) as cranking out code.
Open World ModelBut RDF is more than a relational database, as it is tailored to the needs of the World Wide Web. In particular it is based on an "Open World Model" rather than "Closed World Model", and also expects that data may arrive as a chaotic, multi-valued, arbitrary graph.
So rather than having to constantly revise applications and their data schemes as needs change, RDF Schema applications anticipate change (including the inevitable conflicts) and support aging gracefully.