Directory Service

The directory service is for use by network administrators. It allows them to set access controls on the domain for each user account. This is an abstraction layer allowing the administrator to customize each users requirements while keeping sensitive information out of reach. this is a service rather than a physical directory on the hard disk drive. The data pertaining to it is stored in files which store information about Preferences, Subscribers, Devices, Content, namespace, and more. The users are granted permission by the administrator for these types of information.
The directory service is a components of the Network Operating System (NOS) and is an information sharing system used for finding, organizing, administering, and managing network information such as user groups, printers, folders, files, and other resources.
Over the years, standards have been developed by the International Telecommunications Union (ITU) and the International Organization for Standardization (ISO) to provide interoperability across several vendor platforms. These are standard systems of organizing objects in logical order which is called the X.500 by ITU and ISO/IEC 9594. These standards apply to mail exchange and looking up names.
Many companies have adopted these protocols and have systems to handle directory services such as Apache which has a service called ApacheDS, and Novell which offers eDirectory. Windows has the Active Directory which is installed on the Windows 2000 and 2003 Server systems.
Identity management programs create another layer of security on objects that can be identified such as devices, applications, countries, or organizations. Each object is identified by certificates encoded within each object, and each certificate contains an issuer and a subject. Without these correct certificates, users within a network our outside the network can be denied access.