objectClass

objectClass is an LDAP (Lightweight Directory Access Protocol) attribute used to declare the schema-defined classes that apply to a directory entry. The values reference object class definitions from the directory’s schema and determine what kind of entity the entry represents and which attributes may or must be present.

In typical LDAP usage, an entry lists one structural object class that defines its primary type, along with zero or more auxiliary object classes that extend the entry’s attributes. The objectClass values are usually given as names or OIDs and are multi-valued. The schema specifies, for each object class, a set of mandatory (MUST) and optional (MAY) attribute types, as well as its place in the class hierarchy via SUP (superclass) and whether the class is structural or auxiliary.

A key concept is the distinction between structural and auxiliary object classes. The structural class defines the entry’s main type, while auxiliary classes add additional attributes without changing the entry’s structural identity. The root of all object classes is the top class, which is abstract and rarely used directly.

Common practice uses a chain such as top, person or organizationalPerson, and often inetOrgPerson for human-facing entries. This combination implies inherited attributes (for example, common name, surname) and allows additional attributes like mail or telephone numbers through auxiliary classes.

In modeling and directory administration, the objectClass attribute is central to data structure, validation, and querying, as it governs which attributes are valid for an entry and how entries relate within the directory schema.