This section is from the "Practical PostgreSQL" book, by John Worsley and Joshua Drake. Also available from Amazon: Practical PostgreSQL.
To ensure compatibility with earlier versions of PostgreSQL, the developers have continued to provide the older datetime and timespan data types. The datetime type is now equivalent to timestamp , while the timespan is now equivalent to the interval types.
Other date/time data types include abstime and reltime , which are lower precision types. However, these types are internal to PostgreSQL, and any or all of these types may disappear in a future release. It is advised therefore to design new applications with the SQL-compliant data types in mind, and to convert older applications from any of these data types as soon as is possible.
 
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