Design: Use case Realization
1. OO design: The bridge between analysis and programming
User-interface, networks, control, security and database requires design tasks and models
2. Interactive process of OO design
a. Create preliminary design class diagrams model
b. Develop interaction diagram for each use case or scenario
c. Return to design class diagram
d. Partition design class diagram into related functions using package diagrams
3. Design class diagram
a. Standard design classes
Entity: design identifier for problem domain class
Boundary: designed to live on system’s automation boundary
Control: mediate between boundary and entity classes, between the domain layer and view layer.
Data access: retrieve from and send data to database.
b. Design principles:
Encapsulation: each object is self-contained unit that include data and method.
Object reuse: designers often reuse same classes for windows components.
Information hiding: data associated with object is not visible to outside world.
Navigation visibility: object is able to view and interact with outside object.
c. Coupling and cohesion:
Coupling: qualitative measure of how closely classes in a design class diagram are linked.
Cohesion: qualitative measure of consistency of functions within a single class.
4. Interaction diagrams: realizing use case and define methods.
a. First-cut sequence diagram:
Start with elements from SSD.
Replace: system object with user case controller.
Add other objects to be included in use case.
Determine other messages to be sent
b. Design with collaboration diagrams;
Sequence diagram: because use case descriptions and dialog follow sequence of steps
Collaboration diagrams: emphasizes coupling.
5. Package diagram: structuring the major components
a. Indentifies major components of a system and dependencies.
b. Determines final program partitions for each layer: view, domain, data access.
c. Can divide system into subsystem and show nesting within packages.
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