Components of the Distributed Database and Related Protocols


The following is a discussion of the components and related protocols of the X.500 Directory service . The overall structure of the X.500 Directory should first be understood , and this done with the aid of the diagram below . This is then preceeded by an in-depth discussion of the Directory components and protocols .

Overall Structure


The X.500 Directory service is maintaind as a Distributed Database which can be accessed to provide the user with important services . The purpose of these services is to allow users to engage in dialogue with other open end systems . In order to achieve this , (the main function of the Directory System) , knowledge of exsistance , in relation to the end user , and presentation addresses must be provided , along with other relevent information . To gain a better understanding of the X.500 service , the following is a discussion of the components that constitute the Distributed Directory .

As can be seen from the model of the Directory , it can be viewed from three levels of abstraction . The first can be viewed as the complete Directory system as a whole , with the interface of the Directory user . The user of the open end system does not interact directly with the directory , but instead it interacts with a Directory User Agent (DUA) . The DUA requests services from the DSA on behalf of the Directory user .


At a more detailed level of abstraction , it is possible to view the Directory system and identify that it consists of a number of individual components which are known as Directory System Agents (DSA) . These components co-operate to provide the service that the user has requested , and are also used to maintain the Directory .


Looking at the third and final level of abstraction , the DSA can be examined to reveal how it structured and indeed how it functions . The DSA consists of both Internal Processes which deal with the users requests and a Data Store of the relevent information . The DSA's Data Store has a tree-like structure which also contains part of the global DIT . The DSA's Internal Processes are described in terms of their interactions with the DSA's information tree . Each node in the tree is known as a DSA Specific Entry (DSE).