CSCE 431 Lecture 8

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Finding Design Classes

advice:

• Reuse code and existing solutions
• avoid bugs and reinvention
• consider abstractions as "machines" rather than "objects"

Finding Implementation Classes

Reuse!

• standard library

Different Kinds of Objects

Following categories can be identified

entity objects

persistent information tracked by system

application domain objects ("business objects")

boundary objects

interaction between user and system

control objects

control tasks performed by the system

Note: Think MVC architecture.

Example: Digital Watch

Entities:

• year
• month
• day

Control:

• Changedate

Bundaries:

• Button
• LCDDisplay

Identifying Entity Objects

• Recurring nouns in requirements
• Real-world entities and processes that system must track
• Data sources (sensor) or sinks (outputs)

Identifying Boundary Objects

• Collect information from user
• translate information into format for entity and control objects
• UI controls to initiate actions
• Forms to enter data
• Messages the system uses to respond

Identifying Control Objects

• Coordinate boundary and entity objects
• Do not have concrete counterpart in real world
• Identify one control object per business task

More UML

Sequence Diagram

• Ties use cases with objects
• Distributes behavior among participating objects
• more concise (and possibly more precise) than text-based descriptions
• Encapsulates lifetime of objects («create» and «delete»)

State Machine Diagram

Represents Behavior from single object's perspective (versus use-case perspective) More abstract than a simple hardware-based FSM diagram