For FB >= 2.0
COMMENT ON <object> IS {'sometext' | NULL}
<object> ::= DATABASE
| <basic-type> objectname
| COLUMN relationname.fieldname
| PARAMETER procname.paramname
<basic-type> ::= CHARACTER SET | COLLATION | DOMAIN | EXCEPTION
| EXTERNAL FUNCTION | FILTER | GENERATOR | INDEX
| PROCEDURE | ROLE | SEQUENCE | TABLE | TRIGGER | VIEW
This is compatible with FB 3.0 In FB 3.0 changes in system tables are not allowed.
eg.
UPDATE RDB$RELATION_FIELDS
SET RDB$DESCRIPTION = 'some_desc'
WHERE RDB$FIELD_NAME = 'RDB$DESCRIPTION' AND RDB$RELATION_NAME = 'table_name'
does not work in fb 3.0
</basic-type></basic-type></object></object>