The Orion 2.0 system provides built-in support for uncertainty at the database level. By extending the query processing engine of PostgreSQL, Orion natively manages uncertain data modeled as arbitrary joint probability distributions. Orion 2.0 is a complete redesign and rewrite of its predecessor U-DBMS [4], and includes the following new and innovative contributions [15]:

- An integrated implementation (within PostgreSQL) of the data model in [18], which is consistent with Possible Worlds Semantics (PWS) and supports both continuous and discrete uncertainty.
- Efficient access methods for querying uncertain data, including three index structures based on R-trees, signature trees, and inverted indexes [6,16].
- Improved query optimization, join algorithms, and selectivity estimation by gathering and exploiting additional statistics over probabilistic data types [5,17].
- Integration with for graphical visualization of and statistical inference over uncertain data [8].

The system architecture of Orion 2.0 is given in Figure 1. A detailed explanation of different components in the architecture is given in Section 3.

Rohit Jain 2011-08-02