This User object class defines many attributes, such as the user's name, telephone number, address, and group memberships. An object is a specific instance of an object class. You can extend the schema by defining new object classes. Attributes hold a piece of information that describes an object. This information is the attribute value.
Attribute values can be multi-valued.
That is, you can assign more than one value to a single attribute. Administrators and applications define values for the attributes. If an attribute is optional, administrators or applications don't need to assign a value to create an instance of the object. However, if an optional naming attribute is the object's only naming attribute, the administrator or application must assign a value to the attribute before they can create the object. Objects must have a name before you can create them.