The replication comes as part of the directory. Application developers need to recognize the implications of this replication as they decide which information to place in the directory and how frequently it is likely to change. Frequent changes force frequent replication, which can swamp the network. However, some developers have latched on to directories as essentially free, replicated databases, although they have shortcomings when it comes to ensuring transaction integrity. As databases, directories have an object-oriented schema that allows the data to be organized into a tree hierarchy rather than the rows and columns and tables of a relational database.
Directories allow entries to be grouped and categorized.
Administrators or developers can then define rules based on information in the directory to control the access to the company's online resources. For instance, all workers on the product engineering team can have access to all product engineering information and applications but cannot access corporate financial applications or human-resources data. The directory is optimized to handle a high number of read operations, typically an order of magnitude greater than write operations. Similarly, the schema is optimized for security and user-access administration and control activities. However, the newest versions of the directories have schemas that can be extended.