INFORMATION_SCHEMA for Firebird

Lorenzo Alberton writes:

"The SQL 2003 Standard introduced a new schema called INFORMATION_SCHEMA. PostgreSQL, SQL Server and now MySQL have it. ORACLE, DB2, Sybase, Ingres, Informix and other DBMS have something similar, usually called System Tables. The INFORMATION_SCHEMA is meant to be a set of views you can query using regular SELECT statements, for instance if you need to know something about the defined triggers, or the structure of a table to which you have access. Firebird doesn't have it, but you can retrieve pretty much everything you need from the system tables. These are metadata tables, their names start with "RDB$". Let's see how we can retrieve some useful informations from them."