1. Jan 15, 200391. 3913 Ron McFadyen1 Ch 9. Use-case model: drawing System Sequence Diagrams Iteration: a simple cash-only success scenario of Process Sale beginning a wide-and-shallow design and implementation touches on many major architectural elements begins with a expansion of the Use Case Model with a System Sequence Diagram to clarify the input and output system events

2. Jan 15, 200391. 3913 Ron McFadyen2 Simple cash-only Process Sale scenario 1. Customer arrives at a POS checkout with goods and/or services to purchase 2. Cashier starts a new sale 3. Cashier enters item identifier 4. System records sale line item and presents item description, price, and running total Cashier repeats steps 3-4 until indicates done 5. System presents total with taxes calculated 6. Cashier tells customer the total and asks for payment 7. Customer pays and System handles payment...

3. Jan 15, 200391. 3913 Ron McFadyen3 System Sequence Diagram a picture showing actors and systems, lifelines, messages, time for a particular scenario for SSDs we will be ignoring an “activation box” that is normally placed on a lifeline :Cashier :System an arbitrary cashier a cashier object the software system to be developed We’ll see it as a black box

4. Jan 15, 200391. 3913 Ron McFadyen4 Sequence Diagram object-oriented systems perform tasks by interacting with each other through the passing of messages a sequence diagram is an interaction diagram that emphasizes the messaging sequence A sequence diagram illustrates the dynamic behaviour of a system of objects The arrow we utilize ( ) is for procedural or synchronous messages – where the sender sends a message, transfers control to the receiving object, and waits for a response To indicate a return message and the explicit return of control, we use Ch 15 discusses interaction diagrams more fully

5. Jan 15, 200391. 3913 Ron McFadyen5 System Sequence Diagram :Cashier :System Message at Time1 from :Cashier to :System Response at Time2 from :System to :Cashier Earlier events are above later events in the diagram time travels downward Time1 earlier than Time2: Time1 < Time2 message response

6. Jan 15, 200391. 3913 Ron McFadyen6 Figure 9.1

7. Jan 15, 200391. 3913 Ron McFadyen7 Figure 9.3 There are 4 system events shown here. The cashier will interact with the system in 4 ways. The events are given operation names: makeNewSale, enterItem, endSale, makePayment.