LDAP Classes and Attributes
Although LDAP entries are really just a collection of attributes, LDAP has the concept of classes. Every LDAP entry has an attribute called objectClass that lists the class hierarchy for an object. Not only does objectClass contain the object's class, it must contain the entire list of superclasses all the way back to the top class. Fortunately, the classes aren't nested too deeply, so the objectClass list is usually fairly small.
One other thing to keep in mind: The class hierarchy doesn't dictate the structure of the directory tree. A node in the directory tree can contain one of its superclasses as a child.
Table 18.1 lists some of the common LDAP classes. The complete set of classes is defined in the standard RFC2256, ...