RSI - A Structured Approach Use Cases and HCI Design

The RSI Approach To HCI Design / Use Case Analysis Page 20 of 42
two activities are so tightly bound that there appears to be a dependency link in both
directions between the activities.
Both forms of iteration occur with RSI, the latter being the relationship between the creation
of the interface use case model and the service use case model.
4.2.2. Increments
An incremental approach to development divides the delivery of a system up into a number of
phases. The criteria by which this division is made may vary, but a functional split is often
used.
SCOPE/REFINE
W5a - RSI LONG PAPER [42 PAGES].doc( Rev: 5) - 03/09/00
use case
model
(stage 1)
increment 3
scope and phase
into increments
increment 2
increment 1
interface model
service model
refers to objects in
refers to
objects in
conceptual
object
model
core
specification
model
RSI favours the functional division of a system at the end of the requirements stage of the
process. The functionality of a particular phase may be determined on the basis of priority
("we just have to have this function.") or risk ("we're not quite sure what we want here.") or
both. Other criteria for incremental phasing (such as managing technical risk) are beyond the
scope of this discussion, and so not considered further here (although in project management
terms they are very important).
4.3. Developing the requirement use case model
The requirement use case model is the first part of the model to be developed, and provides
the starting point from which all other models can be traced.
The process description here assumes some form of ad-hoc project start-up document. On
small projects it may be possible to develop a requirement model from scratch based on
discussions with users. On larger projects, some form of antecedent document will almost
certainly be necessary.