A structural object class is special in that it defines the core type for any entry that contains it.
An object class defined for use in the structural specification of the DIT is termed a structural object class.
Structural object classes are used in the definition of the structure of the names of the objects for compliant LDAP Entry.
Every LDAP Entry is when created characterized by precisely one structural object class superclass chain which has a single structural object class as the most subordinate object class. This "primary" or "naming" objectClass can not be changed after the entry is created.
The structural object class for an entry may be used by other LDAP Schema elements for defining constraints on directory data. The structural object class may be used by a Name Form definition to control the attribute(s) used in the Relative Distinguished Name for the entry, and in turn by a DIT Structure Rule to control the types of parent entries that it may have. The structural object class may also be used by a DIT Content Rule to control the set of AUXILIARY and required, allowed, and prohibited Attribute Types for the entry.