Project Server Interface (PSI) Overview
All Microsoft Windows–based and Web-based client applications for Microsoft Office Project 2007 use the Project Server Interface (PSI), a set of Web services based on the Microsoft .NET Framework 2.0. The PSI, along with the Project Server Eventing Service, exposes the functionality and data that developers need to extend Project Server and to integrate other applications with Project Server. PSI parameters typically include DataSet objects that provide many advantages in development. Datasets correspond to Project Server business object types. Each PSI Web service proxy includes the relevant datasets for public methods within that Web service.
PSI methods are different from the Project Data Service (PDS) methods in earlier versions of Project Server because the PSI is a managed code interface to the middle-tier Project Server business objects, rather than an XML interface that accesses the Project Server database. The PSI can do all of the work the PDS did and much more. The PSI also provides a way to add extensions with custom Web services. PSI extensions have the advantage of using the same Project Server security infrastructure that the rest of the PSI uses.