The methodology examines the system in detail using standard tools, and produces three descriptions of the system under investigation. The success of SSADM may lie in the fact that it has these multiple techniques. Each of the three system models provides a different viewpoint of the same system, each of which are required to form a complete model of the system. Within SSADM, each of the three techniques is cross-referenced against the others to ensure the completeness and accuracy of the complete model.
The three views gained are:
- The Data View: a description of all the data and information the system uses (gained from the DFDs above)
- The Process View: a description of all the processes or actions carried out by the system (taken from the process descriptions and the process catalogue)
- The Event View: a description of the systems events, that is the 'triggers' that set processes running (from the Entity life histories)
Taking these different views allows us to gain much more information about the system than we could have done otherwise.
Finally we take the current system and apply the requirements to it, and this gives us our required system.
Why use SSADM?
Within government departments (in the UK) SSADM has to be used. External contractors producing software for the government also have to use SSADM.
Other companies, ie non-government contractors and companies, use SSADM because they expect that the use of a disciplined 'engineering' approach will eventually improve the quality of the systems they produce.
Many companies have been willing to incur the considerable expense of implementing SSADM (eg staff training) with this expectation in mind.