Software Engineering System Modeling Chapter 5 (Part 1) Dr.Doaa Sami Modified from Sommerville’s originals

10 A. Context Models

Context Models 11  Context models normally show that the environment includes several other automated systems. However, they do not show types of relationships between the systems in the environment and the system that is being specified.

Context Models (Example) 12  In developing the specification for MHC-PMS system, you have to decide if the system should focus exclusively on collecting information about consultations (using other systems) or it should collect personal patient information.  Advantage of relying on other systems for patient information is that you avoid duplicating data.  Disadvantage is that using other systems may make it slower to access information. MHC-PMS cannot be used if these systems are unavailable.

The Context of the MHC-PMS 13

14 B. Interaction Models

15 1. USE CASE Diagrams

Use Case Notation  Example: ATM banking system. 24 System boundary Actor ATM Withdraw cash Check balance Customer Use cases

<<extend>> 27  An extension is a significant exception to the normal case.  Use an extend link to show that one use case may add functionality to another use case under certain circumstances.  Major variation: If you have an alternative path in the use case, especially when something goes different from what does plan.  Optional sub-goal: If you have parts of the use case that would be optional to implement or execute to meet the actor’s goals. Doing so clarifies the relationships between actors and their goals. It also emphasizes that you may deliver these optional goals in later releases.

<<extend>> 28  The arrow should point at the main, extended use case.  For example, the Login use case of a typical Web site can involve Register New User - but only when the user does not already have an account

<<include>> 29  Used to indicate that one use case includes the functionality of another use case.  Some use cases may share one or more common steps  The arrow should point at the more detailed, included use case.

Generalization 30  Generalization between Use Cases means that the child is a more specific than the parent; the child use case inherits all attributes and associations of the parent use case, but may add new features.  Children of the same parent are all specializations of the parent.

Generalization 31

Generalization 32

Use Case Specification Outline Example 35 Use Case: Withdraw Money Actors: system user Precondition: 1. The Customer has selected a language to use. 2. The Customer is a member of a bank. 3. The Customer has placed their credit card into the ATM machine. 4. The Customer has verified their account with PIN number. Trigger: Customer selects withdraw money from the transaction options list. Flow of events: 1. The use case starts when the Customer selects withdraw money from the transaction options list.. 2. The system then checks this chosen amount against Customer’s current account balance. 3. The system shows a confirmation message that the withdraw money transaction was successful. 3.1. If the Customer does not have sufficient funds for the withdraw amount a message is displayed and they are requested to supply a different withdraw money amount. 4. The system then counts up money notes to the value of the withdraw amount and places it in the cash dispenser. 5. The system ask the user if they need a receipt 5.1. If the Customer selects “No” then a transaction receipt is not printed. 5.2. If the Customer selects “yes” then a transaction receipt is printed. 5.2.1 if there is no papers, a message is displayed “Sorry receipt cannot be printed”. Post condition: 1. The system has updated the Customer’s account balance if a transaction was successfully completed. 2. The system has ejected the Customer’s account card if no other transactions were required.