PostgreSQL is an object-relational database management system (ORDBMS) based on POSTGRES, Version 4.21, developed at the University of California at Berkeley Computer Science Department. 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.

PostgreSQL has a variety of Unix platforms and also runs on Windows with the help of Cygwin framework ( http://www.cygwin.com/ ). 

PostgreSQL is an open-source descendant of this original Berkeley code. It provides SQL92/SQL99 language support and other modern features. PostgreSQL  is a free database system that is taking stabs at proprietary database systems like Oracle, SQLServer, and DB2

POSTGRES pioneered many of the object-relational concepts now becoming available in some commercial databases. Traditional relational database management systems (RDBMS) 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, this simplicity makes the implementation of certain applications very difficult. 

PostgreSQL offers substantial additional power by incorporating the following additional concepts in such a way that users can easily extend the system:

• inheritance

• data types

• functions

Other features provide additional power and flexibility:

• constraints

• triggers

• rules

• transactional integrity

These features put PostgreSQL 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 traditional relational database languages. So, although PostgreSQL has some object-oriented features, it is firmly in the relational database world. In fact, some commercial databases have recently incorporated features pioneered by PostgreSQL.