A Unified Approach to OOD

22.1.4 A Unified Approach to OOD

In Chapter 21, we noted that Grady Booch, James Rumbaugh, and Ivar Jacobson com- bined the best features of their individual object-oriented analysis and design meth- ods into a unified method. The result, called the Unified Modeling Language has become

WebRef

widely used throughout the industry. 4 An extensive tutorial and

listing of UML resources During analysis modeling (Chapter 21), the user model and structural model views

including tools, papers, are represented. These provide insight into the usage scenarios for the system (pro- and examples can be

viding guidance for behavioral modeling) and establish a foundation for the imple- found at

mini.net/cetus/

mentation and environment model views by identifying and describing the static

oo_uml.html

structural elements of the system. UML is organized into two major design activities: system design and object design. The primary objective of UML system design is to represent the software architecture. Bennett, McRobb, and Farmer [BEN99] discuss this issue in the following way:

In terms of object-oriented development, the conceptual architecture is concerned with the structure of the static class model and the connections between components of the model. The module architecture describes the way the system is divided into subsystems or mod- ules and how they communicate by exporting and importing data. The code architecture defines how the program code is organized into files and directories and grouped into libraries. The execution architecture focuses on the dynamic aspects of the system and the communication between components as tasks and operations execute.

The definition of the “subsystems” noted by Bennett et al. is a primary concern dur- System design focuses ing UML system design. on software

UML object design focuses on a description of objects and their interactions with architecture and the

definition of one another. A detailed specification of attribute data structures and a procedural subsystems. Object 5 design of all operations are created during object design. The visibility for all class

design describes attributes is defined and interfaces between objects are elaborated to define the details objects at a level of

of a complete messaging model. detail that can be

System and object design in UML are extended to consider the design of user interfaces, implemented in a

programming data management with the system to be built, and task management for the subsystems language.

that have been specified. User interface design in UML draws on the same concepts and principles discussed in Chapter 15. The user model view drives the user interface design process, providing a scenario that is elaborated iteratively to become a set of interface classes. 6

4 Booch, Rumbaugh, and Jacobson have written a set of three definitive books on UML. The inter- ested reader should see [BOO99], [RUM99], and [JAC99]. 5 Visibility indicates whether an attribute is public (available across all instantiations of the class), private (available only for the class that specifies it), or protected (an attribute that may be used by the class that specifies it and its subclasses). 6 Today, most interface classes are part of a library of reusable software components. This expe- dites the design and implementation of GUIs.

CHAPTER 22

OBJECT-ORIENTED DESIGN

F I G U R E 22.3

Process flow for OOD

Object-oriented analysis System design

Task management

design Object

design

Data management

design Human interface

design

Data management design establishes a set of classes and collaborations that allow the system (product) to manage persistent data (e.g., files and databases). Task manage- ment design establishes the infrastructure that organizes subsystems into tasks and then manages task concurrency. The process flow for design is illustrated in Figure 22.3. 7

Throughout the UML design process, the user model view and structure model view are elaborated into the design representation outlined above. This elaboration activity is discussed in the sections that follow.