An application-specific adapter processes the PSI data based on the rules and conditions listed in the filter and routes the site structure to the desired format. In Conclusion Work on PSI is ongoing. Currently, PSI uses a standard DTD to define its syntax but we plan on migrating it to an RDF schema. We're cleaning up our current code into an LGPL library called psilib and then releasing it through psilib.sourceforge.net . XML is proven in modeling complex hierarchies for open exchange.
Sites are no exception.
Developing PSI has helped us glimpse the underlying patterns of the Web. More connects than divides site structures. We hope to see a standard reflecting this evolve so that any pain from future site evolution comes as a side effect of creation, not transportation. PSI may contribute to this. It may just dimly light the way.