Describing Details of the Happy Path
Now the use-cases have been defined, along with their primary, alternate, and exception pathways. For the Inception phase, we have one more task to do regarding use-cases: describe the details of the happy path. We do this for the happy path (or any other pathway) by outlining the necessary steps to implement the pathway's functionality. As with the previous caveat regarding use-cases, use-case pathways derive from a what perspective, not a how perspective.
A detailed description is necessary so that we can better understand the complexity that might be involved in realizing the use-cases. We need this level of understanding also to estimate both the incremental release strategy and the accompanying time and cost components. The detailed steps of the happy pathway for the Process Orders use-case (A customer calls and orders a guitar and supplies, and pays with a credit card) are identified as follows:
Customer supplies customer number.
Customer is acknowledged as current.
For each product the customer desires:
3.1 Product ID or description is requested.
3.2 Product description is resolved with its ID if necessary.
3.3 Quantity is requested.
3.4 Item price is calculated.
Extended order total is calculated.
Tax is applied.
Shipping charges are applied.
Extended price is quoted to the customer.
Customer supplies credit card number.
Customer's credit card is validated.
Inventory is reduced.
Sale is finalized.
The detailed steps for the pathway are meant to be at a relatively high level. Notice that there are no specific references to technology in the form of, for example, “button clicks” or “scanning.” The details we describe for the pathway will be determined by both the features identified in the charter and any assumptions made about the use-case. Section 4 of the use-case template is a place to document some of the user-centric requirements, as well as throughput requirements. However, it is best to hold off on the user interface portion until the project is closer to producing more design-oriented artifacts. Appendix D contains a complete listing of the detailed steps for the happy path of each use-case.
Most projects seem to work well with the outline format of the use-case details. One reason for this, as cognitive psychologists have known for years, may be that people remember things as outlines in their brains. The processes of driving to the store or fixing your car, for example, are series of predetermined outlines stored away for recall. Another option for documenting Section 3 of the use-case template is the UML activity diagram. We will explore this diagram in Chapter 7; for now, suffice it to say that it is as close to a flowchart as you can get.