There is one subschema entry per server. All entries in the directory have an implied subschemaSubentry attribute type. The value of the subschemaSubentry attribute type is the DN of the subschema entry that corresponds to the entry. All entries under the same server share the same subschema entry, and their subschemaSubentry attribute type has the same value. The subschema entry has the hardcoded DN 'cn=schema'.
The subschema entry belongs to the object classes 'top', 'subschema', and 'IBMsubschema'. The 'IBMsubschema' object class has no MUST attributes and one MAY attribute type ('IBMattributeTypes').