The sysinherits system catalog table stores information about table hierarchies and named ROW type inheritance. Every supertype, subtype, supertable, and subtable in the database has a corresponding row in the sysinherits table.
Column Type Explanation
child INTEGER Identifying code of the subtable or subtype
parent INTEGER Identifying code of the supertable or supertype
class CHAR(1) Inheritance class: t = named ROW type T = table

The child and parent values are from sysxtdtypes.extended_id for named ROW types, or from systables.tabid for tables. Simple indexes on the child and parent columns allow duplicate values.