Single sign-on (SSO) has become something of a Holy Grail in many institutions to the point where many think that that is all identity management is. Anyone who's had to remember multiple user IDs and passwords just to use the email systems and file servers at work understands the pain that comes from having to manage multiple identity credentials.
Beyond causing pain for users, scattered identity data stores cause problems for the business as well. Integrating IT systems is important to businesses because of the added context that develops about a business activity when the data in multiple data stores can be linked. For example, linking the customer billing systems and the customer service systems gives employees processing invoices as well as employees providing customer service additional context about each customer.
For these reasons and more, aggregating identity information and finding the relationship between identity records is important. To aggregate identity data, organizations have four choices:
Build a single central identity data store.
Create a metadirectory that synchronizes data from other identity data stores in the enterprise.
Create a virtual directory that provides a single integrated view of the identity data stores in the enterprise.
Federate directories by tethering identity data stores together.
The first solution is included for completeness, but it's easy to see that creating a single data store of identity data is feasible only ...