Smalltalk and Object Orientation: an Introduction - Free

19. The Object Modeling Technique
19.1 Introduction
This chapter provides an overview of the Object Modeling Technique (OMT). It should not be treated
as a definitive, nor complete, description of the method. For that the reader should see [Rumbaugh et al,
1990] and [Derr 1995]. Instead, this chapter provides an introduction to the basic phases and a summary
of the steps which form each phase. As such it should provide an insight into an object oriented design
(OOD) method.
The chapter first introduces the OMT methodology. The analysis phase is then described in some
detail. The use of use case analysis is included. This is not actually part of OMT (in fact it is part of the
Objectory method of [Jacobson et al 1992]) but is a useful adjunct to the method. The dynamic and
functional models of the analysis phase are described in the next chapter. The design phase (which is
then introduced) and the implementation phase are described in detail in the next chapter.
19.2 The OMT methodology
The OMT methodology consists of several phases. These phases progress a design from (relatively)
early requirements analysis through detailed design to the implementation. The phases are thus: the
analysis phase, the design phase and the implementation phase.
The analysis phase is concerned with understanding and modeling the application and the domain
within which it operates. The OMT book suggests that the initial input to the analysis phase is a
problem statement which describes the problem to be solved and provides a conceptual overview of the
proposed system. This problem statement may be a textual description (as suggested by the authors) or
it might be a more formal description as provided by a technique su ch as OOA or one of the structured
analysis methods in the software engineering field.
The design phase is made up of two sub -phases, the system design phase and the object design
phase. The system design sub -phase is concerned with the overall architectu re of the system. This
architecture is based on the information provided during the analysis phase (in particular the object
model).
The object design sub -phase attempts to produce a practical design by refining, optimizing and
reviewing the models produce d during the analysis phase. This therefore involves moving the focus
away from conceptual objects and towards computer implementation objects. It also involves
identifying appropriate algorithms, ensuring efficient communication between objects and accoun ting
for the flow of control and concurrency issues.
The final phase, the implementation phase, considers how the design should be implemented. It
considers, amongst other issues, mapping a design onto an object oriented language, a data base system
as well as non object oriented languages.
19.3 Analysis phase
The analysis phase is concerned with producing a precise, concise, understandable, and correct model of
the real -world. This is done by constructing a series of models. In particular OMT defines an object
model, a dynamic model and a functional model. OMT does not attempt to construct use case diagrams
to help understand how the system is used and what the main functions of that system are. However, it
is probably a very good idea to start the analysis pha se by carrying out a use case analysis. We will
therefore consider use case analysis before continuing with the OMT method.
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