Directory information tree (DIT) structure rules define which entries might be superior or subordinate to other entries in the DIT.
Together with name forms, DIT structure rules determine how relative distinguished names (RDNs) are added together to make up distinguished names (DNs). Because DITs don't have a global standard and are specific to a company's implementation, each DIT structure rule associates a name form with an object class and specifies each structure rule with an integer rule identifier, instead of an OID number. The identifier defines its relationship, either superior or subordinate, to another object class. If no superior rules are specified, the DIT structure rule applies to the root of the subtree.