Step 7 to Step 8
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Use Case Modeling – Step 7: Structuring Use Cases
After elaborating on the use cases, we find that the Place Order, Register New Member and Archive Membership use cases have a common behavior; they all involve finding the member record from the system. Hence, the inclusion use case Find Member Record is created to cover this common behavior. The revised use case diagram is shown in Figure 4 below.
Figure 7 – The Revised Use Case Model
The revised descriptions of the Place Order use case and the Find Member Record use case are shown in Table 6 and Table 7 respectively.
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Use case name: |
Place Order |
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Use case ID: |
UC 100 |
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Super Use Case: |
|
|
Actor(s): |
Customer Service Assistant |
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Brief description: |
A Customer Service Assistant places an order and then submits it for processing. |
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Pre-conditions: |
The member must have registered with the system. |
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Post-conditions: |
The Customer’s order will be directed to the order processing department for processing. |
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Flow of events: |
Include (Find Member Record). The Customer Service Assistant selects “Place Order”. A new order form and order ID are then generated and displayed. The Customer Service Assistant selects items from the catalog and adds them to the order. Customer Service Assistant submits the order for processing. The system records the order and forwards it to the Order Processing Clerk. |
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Alternative flows and exceptions: |
At any time the Customer Service Assistant can decide to suspend the ordering process and come back to it later, or decide to cancel the order. |
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Priority: |
High |
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Non-behavioral requirements: |
The system should be able to handle 20,000 new orders per day. |
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Assumptions: |
|
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Issues: |
Is there any limit on the amount of an order? |
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Source: |
User Interview Memo 21, 8/6/09 |
|
Use case name: |
Place Order |
Table 6 – Revised Description of the Place Order Use Case
| Use case name: | Find Member Record |
| Use case ID: | UC 10 |
| Brief description: | A member record is requested. |
| Post-conditions: | A membership record is returned. |
| Flow of events: |
The Customer Service Assistant finds the member record by entering the member’s ID or name. The system displays a list of members which match the information entered by the Customer Service Assistant. The Customer Service Assistant selects the required member record. The system then displays the details of that member. |
| Alternative flows and exceptions: |
No member record is found for the customer. |
Table 7 – Description of the Find Member Record Use Case
Developing Instance Scenarios
A use case specifies all possible ways of using a system functionality to achieve a user goal. Sometimes, it is necessary to write some examples (instance scenarios) to illustrate the execution of a complex use case. Instance scenarios are easier for the user to understand, and they are very useful for clarifying any ambiguity in the use case description. The instance scenarios can also serve as test cases for system testing.
A sample instance scenario of the Place Order use case is shown in Table 8.
| Parent use case name: | Place order |
| Parent use case ID: | UC-100 |
| Instance name: | A sales order form is received but the membership number is missing. |
| Instance ID: | UCIS-100-1 |
| Environmental conditions and assumptions: | The name (Peter Chan) and signature of the member are available in the system. |
| Inputs: | A sales order form |
| Instance flow description: |
The Customer Service Assistant enters ‘Peter Chan’ to find the member record. The system then displays a list of members which match the member’s name. The Customer Service Assistant repeatedly selects a member record. The system displays the signature of the member when a member record is selected. The Customer Service Assistant selects “Place Order”. A new order form and order ID are then generated and displayed. The Customer Service Assistant selects items from the catalog and adds them to the order. The Customer Service Assistant submits the order for processing. The system records the order and forwards it to the Order Processing Clerk. |
| Outputs |
The sales order is placed. |
Table 8 – An Instance Scenario of Place Order
Use Case Modeling – Step 8: Prioritizing Use Cases
Table 9 shows an informal ranking of some of the use cases of the mail order system.
| Priority Rank | Use Case | Reason |
| High | Process Order | Directly improves the efficiency of the business process and affects the system architecture. |
| High | Place Order | Same as above |
| High | Find Member Record | Included as part of the Place Order use case. |
| Medium | Order Goods | Ordering goods is less often than processing order but still is one of the major business processes. |
| Medium | Deliver Goods | Can improve the control of stock level of goods. |
| Low | Update membership record | Small impact on the system architecture. |
| Low | Register New Member | Same as above. |
Table 9 – Priority Ranking of Use Cases
Figure 8 – Priority Ranking of Use Case in VP.