1. Dr.Basem Alkazemi bykazemi@uqu.edu.sa http://uqu.edu.sa/bykazemi

2. Introduction Software design is the process of decomposing a system into components and define the sequence by which these components operate.

3. Design Characteristics It is a problem solving activity It is a process that rakes requirement document as input and produces design document as output Describes the system abstractly Usually represented in UML Involves the definition of business process Reflects system architecture

4. Design Properties Abstraction Data abstraction Procedure abstraction Control abstraction Modularity Coupling Cohesion Information Hiding Interfacing Encapsulation Complexity Structure Size System Architecture Components Dependencies Interaction (Data, Control)

5. Design Methods (1) Functional decomposition System is decomposed into components that each one provides part of that overall functionality of the system. Components functionality may also be decomposed into sub-components that constitute the overall functionality of a component and so on. Every component must define its basic functionality regardless of any other concern.

6. Design Methods (1) Functional decomposition Top-Down design: start at the system level and decompose it into its components. Bottom-up design: start with components and compose them together to form a complete working system Middle-out design: approach mixes the previous two, where system structure is defined and functional components are incorporated into that structure.

7. Layered System Structure

8. Design Methods (2) Data Flow Design External entities: source or destination of a transition. Denoted as Processes: transform of data. Denoted as Data Flows: the movement of data. Denoted by Data Stores: passive storage of data lies between two processes. Denoted by

9. Design Methods (2) Data Flow Design Example: DFD of simple compiler

10. Design Methods (3) Jackson Structured Programming (JSP) Defines the internal working components of a program Distinguishes between elementary & compound components Compound components Control Structure Types Sequence Iteration Selection

11. Design Methods (3) Sequence : Definition: establish the sequence of execution of processes. Notation: Example:

12. Selection : Definition: represents the different routs of control signal. Notation: Example: Design Methods (3)

14. Iteration: Definition: identify processes that execute in loops. Notation: Example: Design Methods (3)

15. Additional JSP notations Passing values (I/O) Design Methods (3)

17. Exercise: Design a program using JSP that calculates the sum of numbers from 1 to 1000.

18. JSPDesign

19. Flowchart Design

20. Design Methods (4) Object-Oriented Design o Identifies: Objects Attributes & services Relationships between objects o Types: Static structure Dynamic structure

21. Object-Oriented Design Static structure Class Diagram: is a graph in which nodes are objects & edges are relationships. Relationships types: Generalization- Specialization Association Composition

22. Object-Oriented Design Generalization-Specialization

23. Object-Oriented Design Association

24. Object-Oriented Design Composition

25. Object-Oriented Design Dynamic structure 1. State-machine diagram (STD): expresses the possible states of objects and the transitions between the different states.

26. STD Example: ATM

27. Object-Oriented Design Dynamic structure 2. Sequence Diagram: describes the interaction between objects at run-time as it expresses messages passed between objects.

28. Example: ATM Validation Process

29. Summary Design is a problem solving activity that takes requirement document as an input to produce design document as an output Design methods can be classified into: Functional based Data based Control based System Architecture based