Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A directory service can provide white page and yellow page services in distributed computing environments. It allows people and applications to look up other people or services in a hierarchical database. See "Directory Services" for a general description.

Microsoft Active Directory combines features of the Internet's DNS (Domain Name System) locator service and X.500 naming. With it, administrators can unify and manage multiple name spaces over heterogeneous systems. The core protocol for the service is LDAP (Lightweight Directory Access Protocol), which allows the service to work across operating system boundaries and integrate multiple name spaces. Because of this cross-platform capability, administrators can manage other vendors' directory services from Active Directory and reduce administrative workload.