Object classes

An object class specifies a set of attributes used to describe an object. For example, if you created the object class tempEmployee, it could contain attributes associated with a temporary employee such as, idNumber, dateOfHire, or assignmentLength. You can add custom object classes to suit the needs of your organization. The IBM Directory Server schema provides some basic types of object classes, including:

• Groups
• Locations
• Organizations
• People

Object classes are defined by the characteristics of type, inheritance, and attributes.

Object class type

An object class can be one of three types:

Structural:

Every entry must belong to one and only one structural object class, which defines the base contents of the entry. This object class represents a real world object. Because all entries must belong to a structural object class, this is the most common type of object class.

Abstract:

This type is used as a superclass or template for other (structural) object classes. It defines a set of attributes that are common to a set of structural object classes. These object classes, if defined as subclasses of the abstract class, inherit the defined attributes. The attributes do not need to be defined for each of the subordinate object classes.

Auxiliary:

This type indicates additional attributes that can be associated with an entry belonging to a particular structural object class. Although an entry can belong to only a single structural object class, it might belong to multiple auxiliary object classes.

Object Class Inheritance

This version of the Directory Server supports object inheritance for object class and attribute definitions. A new object class can be defined with parent classes (multiple inheritance) and the additional or changed attributes.

Each entry is assigned to a single structural object class. All object classes inherit from the abstract object class top. They can also inherit from other object classes. The object class structure determines the list of required and allowed attributes for a particular entry. Object class inheritance depends on the sequence of object class definitions. An object class can only inherit from object classes that precede it. For example, the object class structure for a person entry might be defined in the LDIF file as:

objectClass: top
objectClass: person
objectClass: organizationalPerson

In this structure, the organizationalPerson inherits from the person and the top object classes, while person object class only inherits from the top object class. Therefore, when you assign the organizationalPerson object class to an entry, it automatically inherits the required and allowed attributes from the superior object class (in this case, the person object class).

Schema update operations are checked against the schema class hierarchy for consistency before being processed and committed.

Attributes

Every object class includes a number of required attributes and optional attributes. Required attributes are the attributes that must be present in entries using the object class. Optional attributes are the attributes that can be present in entries using the object class.