Page 25 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Unit 2: Modelling Concepts

volumes of information and fewer overall items. As we move to lower levels of abstraction, we Notes
reveal more detail, typically encounter more individual items, and increase the volume of
information with which we must deal.
We also note that there are many different types of abstraction.
For example, functional abstraction, data abstraction, process abstraction and object abstraction.
Usually, abstraction is not defined in terms of information hiding.

For example, note the use of words such as ‘ignore’ and ‘extracting’. However, we should also
note the use of the words ‘suppress’ and ‘suppressing’ in some of the examples.
In short one might say that abstraction dictates that some information is more important than
other information, but (correctly) does not specify a specific mechanism for handling the
unimportant information.

Self Assessment

Fill in the blanks:

9. .................... is a simplified description, or specification, of a system that emphasizes some
of the system’s details or properties while suppressing others.
10. Abstraction, as an ...................., denotes a model, a view, or some other focused representation
for an actual item.
11. When you are using abstraction during analysis, you have to deal with .................... concepts.

2.4 Three Models

Whole object oriented modeling is covered by using three kinds of models for a system
description. These models are:

Object model,
Dynamic model, and
Functional model
Object models are used for describing the objects in the system and their relationship among
each other in the system. The object model encompasses the principles of abstraction,
encapsulation, modularity, hierarchy, typing, concurrency, and persistence. The Object-Oriented
analysis and design is fundamentally different than traditional structured design approaches; it
requires a different method of thinking about decomposition, and it produces software
architectures that are largely outside the realm of the structured design culture. These differences
arise from the fact that structured design methods build upon structured programming, whereas
object-oriented design builds upon object-oriented programming.
The dynamic model describes interaction among objects and information flow in the system.
The dynamic model shows the time dependent behavior of the system and the objects in it.
Begin dynamic analysis by looking for event, externally visible stimuli and responses.

Notes The dynamic model is important for interactive systems, but insignificant for
purely static data repository, such as database.

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