1. Agenda Schedule Assignment 2 Due Next week [Nov 25 th ] Quiz No 04 – SSDs & Sequence Diagrams Today Review last week Review ICE-08 from last week Sequence Diagrams (Continued) View & Data Layers Cohesion & Coupling Sheridan Object Oriented Methods 1

2. Moving from System Sequence (SSD) to Full Sequence Diagrams Design phase requires details on how to program To this point we have: List of all the things the system must be able to do. [Use Cases] Defined how each use case works. [Activity diagrams/narratives] Identified all the things the system must keep track of. [Classes] Real World Example: What it does. [Wash clothes] How it does it. Adds water & agitates Rinses Spin dries Drains water Look at how the Washer System is designed. It’s composed of various parts (objects) Sheridan Object Oriented Methods 2

3. Sheridan Object Oriented Methods 3 Review ICE-08

4. Sheridan Object Oriented Methods 4

5. Review ICE-08 Sheridan Object Oriented Methods 5

6. Review ICE-08 Sheridan Object Oriented Methods 6

7. Sheridan Object Oriented Methods 7

8. Review ICE-08 Sheridan Object Oriented Methods 8

9. Quick Review of Last Week Constructing Sequence Diagrams Select the Use Case Identify Object responsibilities Create the Design Class Diagram Identify the domain class object that has responsibility for the use case. (it receives the first message from the controller) Identify the other classes that must collaborate with the primary object class to complete the use case. Sheridan Object Oriented Methods 9

10. Next Step… Build the Sequence Diagram Add a > object Add the > objects Sequence the messages Sheridan Object Oriented Methods 10

11. Layered Design [1] Smaller systems View layer Business logic layer SQL statements are included in the methods of the domain classes Sheridan Object Oriented Methods 11

12. Layered Design [2] Larger systems View Layer Business Logic Layer Data Access Layer Sole responsibility is to execute database SQL statements Get the results and provide the information to the business logic layer Sheridan Object Oriented Methods 12

13. Data Access Layer Two ways to instantiate a Customer object in memory from a data base. Approach 1 Using the constructor of each domain object Approach 2 Using the data access layer object. Sheridan Object Oriented Methods 13

14. Sheridan Object Oriented Methods 14 Approach 1

15. Sheridan Object Oriented Methods 15 Approach 2

16. Example – eCommerce System Use Case: “Cancel Order” [1] Sheridan Object Oriented Methods 16

17. Example – eCommerce System Use Case: “Cancel Order” [2] Sheridan Object Oriented Methods 17

18. Example – eCommerce System Use Case: “Cancel Order” [3] Sheridan Object Oriented Methods 18

19. Final Step:- Add View Layer Sheridan Object Oriented Methods 19

20. “Pick-Up Car” Sequence Diagram Sheridan Object Oriented Methods 20

21. Sheridan Object Oriented Methods 21

22. Some Fundamental Design Principles Coupling Measures how closely classes are linked Cohesion Measures the consistency of functions in a class Sheridan Object Oriented Methods 22

23. Coupling & Cohesion -Fundamental Design Principles Coupling – qualitative measure of how closely classes in a design class diagram are linked Number of navigation arrows in design class diagram or messages in a sequence diagram Loosely coupled – system is easier to understand and maintain Cohesion – qualitative measure of consistency of functions within a single class Separation of responsibility – divide low cohesive class into several highly cohesive classes Highly cohesive – system is easier to understand and maintain and reuse is more likely Sheridan Object Oriented Methods 23