Linked Attributes

Linked attributes are pairs of attributes in which the system calculates the values of one attribute (the back link) based on the values set on the other attribute (the forward link) throughout the forest. A back-link value on any object instance consists of the distinguished names (DNs) of all the objects that have the object's DN set in the corresponding forward link. For example, "Manager" and "Reports" are a pair of linked attributes, where Manager is the forward link and Reports is the back link. Now suppose Bill is Joe's manager. If you store the DN of Bill's user object in the "Manager" attribute of Joe's user object, then the DN of Joe's user object will show up in the "Reports" attribute of Bill's user object.

A forward link/back link pair is identified by the linkID values of two attributeSchema definitions. The linkID of the forward link is an even, positive, nonzero value, and the linkID of the associated back link is the forward linkID+1. For example, "Manager" is linkID 42, "Reports" is 43.

If you are defining a new pair of linked attributes, you must follow these rules:

• The linkID values must be unique for linkIDs of all attributeSchema objects. See Example Code for Finding the Next linkID.
• A back link must have a corresponding forward link, that is, the forward link must exist before a corresponding back link attribute can be created.
• A back link is always a multi-valued attribute. A forward link can be single-valued or multi-valued. Use a multi-valued forward link when there is a many-to-many relationship.
• The attributeSyntax value of a forward link must be 2.5.5.1, 2.5.5.7, or 2.5.5.14. These values correspond to syntaxes that contain a distinguished name, such as the DN syntax.
• The attributeSyntax value of a back link must be 2.5.5.1, which is the DN syntax.
• By convention, back link attributes are added to the mayContain value of the Top abstract class. This enables the back link attribute to be read from objects of any class (since they aren't actually stored with the object but are calculated based on the forward link values).