For Each Use Case:
1) Identify the Actors
Actor: Someone or something that interacts with, or uses, the system to achieve a desired goal
An actor may be: A user of the system. Describe the user by their role An individual who is not an user (customer, client, etc) The System under Discussion (SuD). Describe it as “the system” Another system (external entity)
2) Identify the Goal
Goal: The aim, or purpose – Goals summarize system functionality in terms of use from a business perspective
Identify the Goal: From the high-level scenario By brainstorming By asking “What does this Actor want to do?”
3) Define the Pre-Conditions
Pre-Condition: Something that must happen before the Use Case can start; something that must be in place before the Use Case can start
Identify Pre-Conditions by asking: “What must be in place for the Use Case to begin?” “How do you know you need to do this?”
4) Define the Post-Conditions
Post-Conditions: The result, or successful outcome of the Use Case
Identify the Post-Conditions by asking: “What is the successful result of this process or Use Case?”
5) Describe the Main Flow
Main Flow: Also known as Primary Scenario A single thread of events The simplest sequence – everything goes right Ideally, no branching – make a note of relevant variations Starts with pre-conditions and ends with post conditions
Describe the Main Flow by asking: “What must happen to achieve the goal / outcome?” “What does the actor need to do next?” “What might happen next?” “What do you need to do to get from the trigger to the outcome?”
6) Describe the Exceptions
Exceptions: Created to describe the failure situations Things that may go wrong in the Use Case
Discover exceptions by asking: “What could go wrong?”
7) Describe the Alternate Flows
Alternate Flows: Created to describe the variations to the Main Flow Results in successful outcome Also referred to as scenarios Listen for “sometimes”, “maybe”, and “it depends”
Discover alternate flows by asking: “What might affect this Use Case?”
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