Please see our SIGMOD 2008 demo paper for the most recent high-level overview of the Orion project and system architecture.
Orion is primarily written in C, with some portions at the user level in PL/pgSQL. The above figure gives a high level overview of the system architecture. The shaded regions represent new components that correspond to the primary features of the Orion data model. Partially shaded boxes highlight portions of the PostgreSQL backend we extended to support queries over uncertain data. Clear boxes (which include the majority of the PostgreSQL backend) indicate components we have not modified.