High Quality CodeWhy it matters.

By Ryan Ruzich

Design

Definition: Software Design means the conception, invention, or contrivance of a scheme for turning a specification for computer software into operational software.

Challenges in Design

Horst Rittel and Melvin Webber defined a “wicked” problem as one that could be clearly described only by solving it, or by solving part of it.

Essentially, this implies you have to “solve” the problem in order to define it, and solve it again to create a solution that works.

Challenges in Design

Design is a sloppy processDesign is about tradeoffs and prioritiesDesign involves restrictionsDesign is nondeterministic (multiple

ways to solve each part)Design is a heuristic process (rules of

thumb)Design is emergent(evolves over time).

Desireable Characteristics of a DesignMinimal ComplexityEase of MaintenanceLoose CouplingExtensibilityReusabilityHigh Fan-inLow-to-medium Fan-inPortability

Desireable Characteristics of a Design ContLeannessStratificationStandard Techniques

5 Levels of Design

Level 1: The complete software systemLevel 2: Divisions into subsystemsLevel 3: Division into classesLevel 4: Division into data and routinesLevel 5: Internal routine design

Heuristics

Because Design is nondeterministic, Software Engineers must follow “rules of thumb”, more commonly known as Heuristics, in their approach to software design.

Some Common Heuristics

Find Real World Objects to base your ADT’s on.

Form Consistent AbstractionsEncapsulate Implementation DetailsInheritanceInformation HidingIdentify Areas Likely to Change and

Isolate them.Keep Coupling of Classes Loose

Common Design Patterns

Reduce Complexity by providing ready-made abstractions

Reduce Errors by institutionalizing details of common solutions

Provide Heuristic Value by suggesting Design Alternatives

Streamline Communication by moving the design dialog to a higher level

Other Heuristics

Aim for Strong CohesionBuild HierarchiesFormalize Class ConstructsAssign ResponsibilitesDesign for TestAvoid Failure

Other Heuristics

Choose Variable Binding (assigning values) time carefully

Make Central Points of ControlConsider using Brute ForceDraw a DiagramModularity

Design Practices

Iterate--Keep iterating at a design process until you arrive at the most optimal

Divide and ConquerTop-Down and Bottom-Up DesignExperimental PrototypingCollaborative Design

Capturing your Design

Insert design documentation into the code itself

Capture design discussion and decisions on a wiki

Write email summaries

Questions?