RSI - A Structured Approach Use Cases and HCI Design

The RSI Approach To HCI Design / Use Case Analysis Page 37 of 42
4.7. Process Variations
A process should at least reflect the cause and effect dependencies that exist between its
deliverables. In the case of RSI, these are that:
• an essential service use case is dependent on one or more steps within the requirement
use case model;
• an interface use cases is dependent on one or more steps within the requirement use case
model;
• a non-essential service use case (those in the consolidated services use case model) is
dependent on one or more interface use cases;
So theoretically at least, we could envisage a project in which the service use cases and
interface use cases were developed as each step within the requirement use case emerged. The
downside of this approach is that it would lead to piecemeal development of service use cases
and interface use cases, which did not consider the more holistic aspects of the analysis and
design process. Hence the emphasis on project increments within RSI. A more holistic view
of the dependencies between RSI deliverables is thus that:
• essential service use cases are dependent on steps within the current increment's
requirement use cases;
• interface use cases are dependent on one or more steps within the current increment's
requirement use cases;
• non-essential service use cases (those in the consolidated service use case model) are
dependent on the current increment's interface use case;
Given this, the following processes could be used for developing the RSI models:
Variation 1:
1. The current increment's requirement use cases are first developed in full;
2. The essential service use case model is developed;
3. The interface use case model is developed;
4. The consolidated service use case and traceability model is developed;
Variation 2:
1. The current increment's requirement use cases are first developed in full;
2. The interface use case model is developed;
3. The consolidated service use case and traceability model is developed;
Both of these approaches maintain the holistic dependencies chain detailed earlier. Experience
has shown that the downside of both these approaches is that they loose the potential synergy
of developing the interface use case and service use case model together (generally in a small
team), and so they should not be considered unless circumstances dictate that the preferred
process is not viable.
W5a - RSI LONG PAPER [42 PAGES].doc( Rev: 5) - 03/09/00