Introduction to Relational Databases

PostgreSQL is a sophisticated Object-Relational Database Management System (ORDBMS). An ORDBMS is an extension of the more traditional Relational Database Management Systems (RDBMS). An RDBMS enables users to store related pieces of data in two-dimensional data structures called tables. This data may consist of many defined types, such as integers, floating-point numbers, character strings, and timestamps. Data inserted in a table is categorized using a grid-like system of vertical columns, and horizontal rows. The relational model was built on a strong premise of conceptual simplicity, which is arguably both its most prominent strength and weakness.

The object-relational aspect of PostgreSQL adds numerous enhancements to the straight relational data model. These include support for arrays (multiple values in a single column), inheritance (child-parent relationships between tables), and functions (programmatic methods invoked by SQL statements). For the advanced developer, PostgreSQL even supports extensibility of its data types and procedural languages.

Due to this object-relational concept, tables are sometimes called classes, while rows and columns can be referred to as object-instances and object-attributes, respectively. We will use this terminology interchangeably in this book. Other SQL data structures, such as indices and views, can be referred to as database objects.


Take care to observe that object-relational is not synonymous with ...

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