Chapter 32. The Information Schema
The information schema consists of a set of views that contain
information about the objects defined in the current database. The
information schema is defined in the SQL standard and can therefore
be expected to be portable and remain stable — unlike the system
catalogs, which are specific to
PostgreSQL and are modelled after
implementation concerns. The information schema views do not,
however, contain information about
PostgreSQL-specific features; to inquire
about those you need to query the system catalogs or other
PostgreSQL-specific views.