Object-oriented analysis and design can offer an approach that facilitates logical, rapid, and thorough methods for creating new systems responsive to a changing business landscape. Object-oriented techniques work well in situations in which complicated information systems are undergoing continuous maintenance, adaptation, and redesign.
In this chapter, we introduce the unified modeling language (UML), the industry standard for modeling object-oriented systems. The UML toolset includes diagrams that allow you to visualize the construction of an object-oriented system. Each design iteration takes a successively more detailed look at the design of the system until the things and relationships in the system are clearly and precisely defined in UML documents. UML is a powerful tool that can greatly improve the quality of your systems analysis and design, and thereby help create higher-quality information systems.
When the object-oriented approach was first introduced, advocates cited reusability of the objects as the main benefit of their approach. It makes intuitive sense that the recycling of program parts should reduce the costs of development in computer-based systems. It has proved to be very effective in the development of GUIs and databases.Although reusability is the main goal, maintaining systems is also very important, and because the object-oriented approach creates objects that contain both data and program code, a change in one object has a minimal impact on other objects.
Chapter Summary
Object-oriented systems describe entities as objects. Objects are part of a general concept called classes, the main unit of analysis in object-oriented analysis and design. When the object-oriented approach was first introduced, advocates cited reusability of the objects as the main benefit of their approach. Although reusability is the main goal, maintaining systems is also very important.
Analysts can use CRC cards to begin the process of object modeling in an informal way. Object Think can be added to the CRC cards to assist the analyst in refining responsibilities into smaller and smaller tasks. CRC sessions can be held with a group of analysts to determine classes and responsibilities interactively.
Unified modeling language (UML) provides a standardized set of tools to document the analysis and design of a software system. UML is fundamentally based on an object-oriented technique known as use case modeling. A use case model describes what a system does without describing how the system does it. A use case model partitions system functionality into behaviors (called use cases) that are significant to the users of the system (called actors). Different scenarios are created for each different set of conditions of a use case.
The main components of UML are things, relationships, and diagrams. Diagrams are related to one another. Structural things are most common; they include classes, interfaces, use cases, and many other elements that provide a way to create models. Structural things allow the user to describe relationships. Behavioral things describe how things work. Group things are used to define boundaries. Annotational things permit the analyst to add notes to the diagrams.
Relationships are the glue that holds the things together. Structural relationships are used to tie the things together in structural diagrams. Structural relationships include dependencies, aggregations, associations, and generalizations. Behavioral diagrams use the four basic types of behavioral relationships: communicates, includes, extends, and generalizes.
The toolset of UML is composed of UML diagrams. They include use case diagrams, activity diagrams, sequence diagrams, communication diagrams, class diagrams, and statechart diagrams. In addition to the diagrams, analysts can describe a use case using a use case scenario.
By using UML iteratively in analysis and design, you can achieve a greater understanding between the business team and the IT team regarding the system requirements and the processes that need to occur in the system to meet those requirements.
LEARNING OBJECTIVES
Once you have mastered the material in this chapter you will be able to:
- Understand what object-oriented systems analysis and design is and appreciate its usefulness.
- Comprehend the concepts of unified modeling language (UML), the standard approach for modeling a system in the object-oriented world.
- Apply the steps used in UML to break down the system into a use case model and then a class model.
- Diagram systems with the UML toolset so they can be described and properly designed.
- Document and communicate the newly modeled object-oriented system to users and other analysts.
