The document discusses handling variations in emerging software design, emphasizing the importance of emergent design, which accommodates unforeseen changes without excessive costs. It outlines practices and principles from extreme programming and design patterns that support effective design and implementation strategies. Recommendations are provided for maintaining design quality while managing variations through various approaches.

2. Handling Variations
in Emerging Designs
Remus Langu
Endava
7th of November 2015

3. Agenda
Nature of Software Development
Emergent Design
Support Practices & Principles
Alternatives in Approaching Variations
Evolutionary Paths
Summary

4. The Nature
of Software Development

5. The Nature
of Software Development

6. Emergent Design
• a way of designing that allows for change,
even unforeseen change, without excessive
costs
• Evolutionary Design/Continuous Design
• based on disciplines, practices, principles,
patterns, wisdom

7. Emergent Design

8. Emergent Design

9. Support Practices
from Extreme Programming
• Refactor Code as Needed
• Write Clearly
• Don’t Do More than You Need
• Programming by Intention
• Write Tests First

10. Lessons Learned
from Design Patterns
• Avoid Redundancy
• Pull Out Things that Vary
• Separate Use from Construction
• Favor Composition over Class Inheritance
• Encapsulate by Convention and Reveal by
Need

11. Support Principles
• S.O.L.I.D.
• You Aren't Gonna Need It
• Don't Repeat Yourself
• Keep It Short and Simple

12. Alternatives
in approaching variations

13. Procedural Approach

14. Object-Oriented Approach (1)

15. Object-Oriented Approach (2)

16. Analogies
between the Two Approaches

17. IF with One Branch
vs. Proxy Pattern

18. IF with One Branch
vs. Proxy Pattern

19. IF with One Branch
vs. Proxy Pattern

20. IF with One Branch
vs. Null Object Pattern

21. IF with One Branch
vs. Null Object Pattern

22. IF with One Branch
vs. Null Object Pattern

23. IF with Two Branches
vs. Strategy Pattern

24. IF with Two Branches
vs. Strategy Pattern

25. IF with Two Branches
vs. Strategy Pattern

26. Which One to Use,
Why, When and How?

27. It depends on different forces

28. Contextual Forces
What domain problem we need to solve?
• business rule variation?
• optionally add some new functionality?
• multiple additional functions, but which and
how many we add varies?
• variation using another variation in a varying
way?

29. Implementation Forces
How to proceed with the implementation?
• Apply the support practices
• Follow the support principles
• Pay attention to the fundamental qualities
like: no redundancy, strong cohesion, correct
coupling, readability, focus & testability

30. Consequent Forces
What will happen once we decide an
approach?
• What is the cost & benefit (gain & loss)?
• Pay attention to testing issues - there is a
deep synergy between testability and good
design.
• Do we get a better design, an under-design
or an over-design?

31. Consequent Forces
Testability is an important consequence of
Good Design

32. Evolutionary Paths

33. From Programming by Intention
to Strategy
Step 1: Add a behaviour using Programming
by Intention

34. From Programming by Intention
to Strategy
Step 2: Pull out what needs to vary using
delegation

35. From Programming by Intention
to Strategy
Step 3: Separate Construction from Use

36. From Programming by Intention
to Strategy
Step 4: Pull out what needs to vary using
inheritance & OCP

37. From Programming by Intention
to Strategy
Step 5: Encapsulate the new variation with
Strategy pattern

38. From Strategy to Adapter
to Façade
Add foreign variation by encapsulating
interface with Adapter

39. From Strategy to Adapter
to Façade
Add foreign variation by encapsulating
interface with Façade

40. Summary
Handling variation in emerging designs
• is done with patterns that encapsulate the
variation
Emergent Design
• allows for unforeseen changes with minimal
costs
• prevents the quality decay of design and code
• avoids under-design & over-design

41. Recommendations

42. Handling Variations in Emerging Designs
Remus Langu
Endava
7th of November 2015
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