directory service

directory service A CLIENT SERVER COMPUTING system consists of a large number of different resources including clients, servers, networks, printers, transmission lines, mass storage devices, and even the users of the system. Programs which execute on such a system will often need to know details about the state of a resource. For example, a program may need to know whether a printer is busy with a long printing job and, if so, where an alternative printer can be found. A directory service provides information on these resources. For example, it might keep data on the name of a server, its physical location, and its current utilisation. Such a service relies on a database of resource details which is continually changing and which is replicated. It is replicated because if the computer on which it is stored malfunctions the whole of a network ceases functioning. Directory services are based on the X500 standard; however, the protocol which this standard is based on (the OPEN SYSTEMS INTERCONNECTION communications PROTOCOL) has been replaced by TCP-IP. Programmers communicate with a directory service using an APPLICATION PROGRAMMING INTERFACE. See also DIRECTORY ACCESS PROTOCOL, LIGHTWEIGHT DIRECTORY ACCESS PROTOCOL, and NAME SERVICE.