The Directory is usually thought of as a distributed database system that is somewhat specialized. Roughly speaking, a database system is said to be distributed when the data is dispersed among several computers on a network and the computers cooperate over the network to provide a coherent database service to the user. The Directory is specialized in ways that allow it to be dispersed among computers that share a world-wide network. This section presents a simplified model of the distributed aspects of the Directory.
The architectural components of the Directory are illustrated in figure 12.3. Each Directory System Agent (DSA) holds a part of the database and also holds information about the location and contents of other DSAs. A user accesses the Directory through a Directory User Agent (DUA). Interaction among DUAs and DSAs is described later in this chapter.
Figure 12.3: Components of the Directory.