Smalltalk and Object Orientation: an Introduction - Free

confirming the users’ needs, their anticipated use, as well as helping to keep them involved in the
development. As the use cases specify the sequences of operations to be performed, the GUI’s can be
made to mimic the desired system behavior. This is a good way of confirming that the use case is
correct. For non-human interfaces any proposed communications protocols can be defined and checked
(for example, that the interacting system is capable of sending and receiving the appropriate
information).
19.3.1.5 Relating the use case model to OMT
The use case model dictates the formation of the models in OMT’s analysis phase as indicated in Figure
19.2. For example,
• it helps identify the primary objects in the object model,
• it helps specify the top level behavior of the system in the dynamic model,
• it helps determine the inputs and outputs provided by, and expected by, the actors for the
functional model.
In addition use cases may also have an influence on ho w the system will be organized into subsystems
as they indicate associated behaviors. In the implementation phase the use cases may be used to identify
suitable scenarios and expected results for integration or system testing.
Use case model
Object
Model
Dynamic
Model
identifies
specifies
Functional
Model
inputs +
outputs
organizes
Subsystem
Model
realized
by
Object
Design
tested in
implemented
by
Test
specification
Source
code
Figure 19.2: How the use case model can be used in OMT
19.3.2 Object modeling
The first step in requirements analysis phase, of the OMT method, is the construction of the object
model. The object model is essentially com prised of the class and object diagrams described in the last
chapter. As with BOOCH and the UML it is the object model which is the core of the OMT
representation. As we have already encountered object models before we will not attempt to explain
what they are other than to state that the object model “shows the static data structure of the real -world
system and organizes it into workable pieces”.
The information for the object model comes from:
• the problem statement (written in natural language according to OMT),
• requirements analysis process such as OOA,
• the domain experts,
• general knowledge of the real world,
• the use case model (if you have constructed one).
An interesting point to note is that OMT claims that object models promote communication betwe
computer professionals and application-domain experts (what do you think?).
OMT suggests the following steps as being an appropriate way in which to construct an object
model.
en
1. Identify objects and classes.
2. Prepare a data dictionary.
3. Identify associations (including aggregations) between objects.
4. Identify attributes of objects and links.
5. Organize and simplify object classes using inheritance.
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