PDS Parity in PSI Web Services
The Project Server Interface (PSI) provides the API for all other applications to access the functionality of Microsoft Office Project Server 2007. The PSI replaces the Project Data Service (PDS) methods in earlier Project Server versions. To help port applications built for Project Server 2003 to Project Server 2007, the PSI provides functional parity for the PDS. You program with datasets in PSI parameters, instead of XML requests for the PDS.
The PSI does not exactly match PDS methods or parameters. For example, some PDS methods are obsolete in Project Server 2007 and some PSI methods address the functionality of several PDS methods.