1.
Software Design

2. 3 SWEBOK KAs covered so far^4
We’ve added one!
Software Requirements
Software Design
Software Construction
Software Testing
Software Maintenance
Software Configuration Management
Software Engineering Management
Software Engineering Process
Software Engineering Models and Methods
Software Quality
Software Engineering Professional Practice
Software Engineering Economics
Computing Foundations
Mathematical Foundations
Engineering Foundations

3. 3 SWEBOK KAs covered so far^4
Software Requirements
Software Design
Software Construction
Software Testing
Software Maintenance
Software Configuration Management
Software Engineering Management
Software Engineering Process
Software Engineering Models and Methods
Software Quality
Software Engineering Professional Practice
Software Engineering Economics
Computing Foundations
Mathematical Foundations
Engineering Foundations
Today’s topic

4. Software Design Subtopics
We’ll touch on a bunch of these today!

5. Much of SE involves designing—be it artifacts, procedures, etc.
What is design?
Create component or process
Not just code
With desired properties
Design objectives/constraints
Involves decision making
Design decisions
Much of SE involves designing—be it artifacts, procedures, etc.

6. What is design? Create component or process With desired properties
Not just code
With desired properties
Design objectives/constraints
Involves decision making
Design decisions
What are some for software components?

7. Some desirable properties for software components
Reusable
Understandable
Modifiable
Extensible
Maintainable
Readable
Reliable
Efficient (as in performance) …
Tradeoffs and prioritization may be necessary!

8. What is design? Create component or process With desired properties
Not just code
With desired properties
Design objectives/constraints
Involves decision making
Design decisions
How to make good decisions?

9. Making software design decisions
Design principles: High-level, fundamental advice
More general
Design patterns: Tried and true template solutions to common problems
More specific
Conform to principles

10. Making software design decisions
Design principles: High-level, fundamental advice
More general
Design patterns: Tried and true template solutions to common problems
More specific
Conform to principles
Example principle:

11. Making software design decisions
Design principles: High-level, fundamental advice
More general
Design patterns: Tried and true template solutions to common problems
More specific
Conform to principles
Let’s see an example pattern

12. Model-View-Controller (MVC) Architectural Pattern
Timeout!
What do we mean by “architectural”?

13. Two levels of software design
Architectural design: High-level structure of software system
Detailed design: Low-level design of individual components/modules/classes

14. Model-View-Controller (MVC) Architectural Pattern
Timeout!
What kind of diagram is this?

15. Data Flow Diagrams
components
flows

16. Model-View-Controller (MVC) Architectural Pattern
Being “architectural”, these components may contain many subcomponents (classes, etc.)

17. MVC Component Responsibilities
Timeout!
What do we mean by “responsibilities”?

18. Responsibility-Driven Design
Frames object design as deciding
How to assign responsibilities to objects
How objects should collaborate
What role each object should play in a collaboration

19. MVC Component Responsibilities
View: Responsible for UI (buttons, etc.)

20. MVC Component Responsibilities
Model: Business logic, domain objects

21. MVC Component Responsibilities
Controller: Translates UI actions into operations on domain objects

22. MVC Component Responsibilities
What principle does MVC follow?

23. MVC Component Responsibilities
What principle does MVC follow?

24. MVC Component Responsibilities
What good properties does this principle/pattern engender?

25. How Rails applies MVC

26. Browser sends HTTP request
How Rails applies MVC
Browser sends HTTP request

27. Router translates to action (method call)
How Rails applies MVC
Router translates to action (method call)

28. Controller performs actions on model
How Rails applies MVC
Controller performs actions on model

29. Model manipulates (CRUD) the database
How Rails applies MVC
Model manipulates (CRUD) the database

30. Model returns data to the controller
How Rails applies MVC
Model returns data to the controller

31. Controller passes data to view
How Rails applies MVC
Controller passes data to view

32. View creates HTML based on data
How Rails applies MVC
View creates HTML based on data

33. Controller sends HTTP response to browser
How Rails applies MVC
Controller sends HTTP response to browser

34. Must you write the entire model/view/controller?
How Rails applies MVC
Must you write the entire model/view/controller?

35. How Rails applies MVC Must you write the entire model/view/controller?
No. Rails provides a framework, and you extend it
But how?

36. Files to extend Rails app/views/… app/controllers/… config/routes.rb
app/models/…

37. Ch. 2 Example: config/routes.rb
“resources” line creates these routes

38. All controllers are part of this class hierarchy
Ch. 2 Example: app/controllers/microposts_controller.rb
All controllers are part of this class hierarchy

39. What kind of diagram is this?
Ch. 2 Example: app/controllers/microposts_controller.rb
Timeout!
What kind of diagram is this?

40. UML Class Diagram
classes
inherits
relation-ship

41. All controllers are part of this class hierarchy
Ch. 2 Example: app/controllers/microposts_controller.rb
All controllers are part of this class hierarchy

42. All model classes are part of this hierarchy
Ch. 2 Example: app/models/micropost.rb
All model classes are part of this hierarchy

43. Ch. 2 Example: app/views/users/index.html.erb
ERb is embedded Ruby –
Combines HTML & Ruby

44. How to “hook into” frameworks (like Rails)
Extend framework classes
Call framework methods
Put files in certain places
Follow naming conventions

45. MVC Question: What code would you change if you wanted to…

46. MVC Question: What code would you change if you wanted to…
… change the colors/style of your webapp?

47. MVC Question: What code would you change if you wanted to…
… change the colors/style of your webapp?
View code

48. MVC Question: What code would you change if you wanted to…
… change how sales tax is calculated?

49. MVC Question: What code would you change if you wanted to…
… change how sales tax is calculated?
Model code
(and maybe Controller)

50. MVC Question: What code would you change if you wanted to…
… add a survey form?

51. MVC Question: What code would you change if you wanted to…
… add a new survey form?
View, Controller, and maybe Model

52. MVC Question: What code would you change if you wanted to…
… add validation that a form input is a legal address?

53. MVC Question: What code would you change if you wanted to…
… add validation that a form input is a legal address?
Model mainly (but maybe Controller and maybe View)

54. MVC Question: What code would you change if you wanted to…
… change the behavior of an existing button?

55. MVC Question: What code would you change if you wanted to…
… change the behavior of an existing button?
Controller (maybe Model, maybe View)

56. What’s next?