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This document is the user manual for the PostgreSQL database management system, originally developed at the University of California at Berkeley. PostgreSQL is based on Postgres release 4.2. The Postgres project, led by Professor Michael Stonebraker, was sponsored by the Defense Advanced Research Projects Agency (DARPA), the Army Research Office (ARO), the National Science Foundation (NSF), and ESL, Inc.
Traditional relational database management systems (DBMSs) support a data model consisting of a collection of named relations, containing attributes of a specific type. In current commercial systems, possible types include floating point numbers, integers, character strings, money, and dates. It is commonly recognized that this model is inadequate for future data processing applications. The relational model successfully replaced previous models in part because of its "Spartan simplicity". However, as mentioned, this simplicity often makes the implementation of certain applications very difficult. Postgres offers substantial additional power by incorporating the following four additional basic concepts in such a way that users can easily extend the system:
| classes |
| inheritance |
| types |
| functions |
Other features provide additional power and flexibility:
| constraints |
| triggers |
| rules |
| transaction integrity |
These features put Postgres into the category of databases referred to as object-relational. Note that this is distinct from those referred to as object-oriented, which in general are not as well suited to supporting the traditional relational database languages. So, although Postgres has some object-oriented features, it is firmly in the relational database world. In fact, some commercial databases have recently incorporated features pioneered by Postgres.