The Global Directory-an overview

The Global Directory, that is the OSI Directory or the X.500 Directory, or, simply `The Directory´, came about because OSI applications, particularly MHS, have a critical need to find information about their potential communications correspondents. Given the need, if the Directory was general enough, it could have very general application. System resources could be located; OSI services found. Organisations could promote their services, using the Directory as a `yellow-pages´ service. So the Global Directory is aimed at a very general need. The main components of the global Directory Service are Directory User Agents (DUAs) and Directory System Agents (DSAs). The former act on behalf of particular users to access the Directory. Here a user might be a person, but might equally well be an OSI application which needs to know about some correspondent