Smalltalk and Object Orientation: an Introduction - Free

20.2.2.5 Specify optimization criteria
Specify any data values which should be maximized (for example, process as many orders in an hour as
possible), minimized (for example, ensure that system response is < 2 milliseconds) or otherwise
optimized.
20.2.3 Adding operations
It is only at this point that the operations in the analysis models are considered. Note how this differs
from the procedural approach in which the operations to be performed would be considered right up
front. The operations are summarized by the object model (but rel ate to functions, actions and events in
the functional and dynamic models). The criteria used for identifying operations are:
• operations implied by events,
• operations implied by state actions and activities,
• operations from functions,
• application / domain operations,
• simplifying operations.
20.2.3.1 Operations implied by events
All the events in the object model correspond to operations (although a single operation may handle
multiple events and vice versa). OMT suggests that during analysis “events are best repres ented as
labels on state transitions and should not be explicitly listed in the object model”. However, if you find
it clearer to list the operations corresponding to the events in the object model; then do so.
20.2.3.2 Operations implied by state actions and activities
The actions and activities in the state diagrams correspond to operations. These can be listed in the
corresponding classes in the object model.
20.2.3.3 Operations from functions
Each function corresponds to one or more operations. The functions should be organized into operations
on objects. This is not as straight forward as it might at first seem since we have not yet associated the
functions with objects.
20.2.3.4 Domain operations
There may be additional domain operations which are not immediately obvious from th e problem
description. These should be identified from additional domain knowledge and noted. For example,
although a cash point system (ATM system) does not allow you to open and close accounts, such
operations are appropriate within the domain and may be important for understanding the domain or for
aspects of the application which have yet to come to light.
20.2.3.5 Simplifying operations
Examine the object model for operations which are essentially the same. Replace these operations with
a generic one. Note that earlier steps may well have generated the same operation but with different
names. Therefore check each object’s operations to see if they are intended to do the same thing even if
they have very different names. Adjust the other models as appropriate.
165