Directory System Agents (DSA)


The following is a description of the Directory system at the second level of abstraction . It involves the interaction of the DSA's to provide the service requested by the user , and to maintain the the Directory Database . Again the interaction between these components is standarised and is called the DSA Abstract Service . Combining this with ACSE and ROSE , a protocol is formed called the Directory System Protocol (DSP) . The DSP consists of the operations , result and errors defined for the DAP , so that the users requsted operation , and the appropriate result can be passed between the user and DSA .


Extra information is added to the users request by the DSA . This information is state related and is used to notify each of the DSA's how much of the operation has been processed so far . The reason for this is so that duplication does not result . This state information is added to the first DSA and gradually modified by other DSA's and finally removed from the result obtained by the first DSA before returning to the user . Each DSA passes on the request and waits for the result to be returned before passing it to the user . The process that has been described is known as chaining . (see fig. 2.0)