Directory Access Protocol (DAP)

A protocol is a mechanism that is used to relay a user's service request between OSI entities . In the case of the X.500 directory service , the protocol used by a DUA to relay a request to a DSA is known as the Directory Access Protocol (DAP) . The DAP is built up from the parameters of the Directory service , as well as from ROSE and ACSE . The following is the abstract service that that is provided to the user .

The services consists of the following operational fields ,

Bind and Unbind operations .
four Interrogation operations .
Abandon operations .
four Modifications operations

Bind and Unbind operations:

The first protocol exchange that must take place between a DUA and DSA is a Directory Binding operation . Before a user (via the DUA) can ask the Directory to perform any of it's operations , DUA must establish a connection to a DSA . In order to establish a connection , certain information is needed which are all parameters of the bind operations . The information is categorised as :

identifcation of protocol used .i.e DAP .
names and addresses of the communicating parties .
security credentials that enable the parties to authenticate each other .

Once the connection has been established and confirmed , the user is able to interrogate or modify the information that is stored in the Directory .

The interrogation operations

1. The Read operation , returns the values of a particular attribute held in a specific directory entry . The input arguments are the combination of a purported name (the users best guess) and an indication of the information that is to be read . The amount of information read can be quantified . The result of this read operation is that the output is the distinguished name of the entry , and requested attribute types and values .

2. The Compare operation , is used to compare a user presented attribute value with those already exsisting in the entry . The input arguments consist of a purported attribute value and again a purported name . The output of the operation is a True/False value indicating if the attribute value is present .

3. The List operation ,, list's the immediate subordinates of an entry . That is to say that , it list's all of the entries that are lower down in the hierarchical tree .

4. The Search operation , is used to search particular portions of the DIT and return selected information about selected entries . The input arguments identify the base entry from which to start the search , the portion of the DIT to be searched and what information should be returned from the selected entries .

The Abandon operation

This basically allows the user to abandon all of the before mentioned operations of the DAP . It only has one argument which identifies the operation that the user would like to abandon . Unfortunately , the abandon operation may no always work , which would then produce an error and the operation that was meant to be abandoned would simply carry on regardless .

four Modification operations

The four Modification operations are all fairly self-explanitory and consist of the following :

Add entry .
Remove entry .
Modify Distinguished Name .
Modify entry .