How to write use cases

Source: Steve's blogs http://soa-java.blogspot.com/

How to find use cases:
1. identify the system boundary
2. identify the primary actors
3. identify the goals of the primary actors
4. define use cases to satisfy those goals

Do:
• use UI-free style e.g. the student authenticates himself
• be terse
• uml (use case) diagrams are just supplements/optional
• focus on the users/actors and their goals than tasks
• use a verb as a name

Don't:
• UI specific e.g. the student fills his name in the username-inputbox at the right corner then clicks the OK button next to this inputbox
• describe the internal workings e.g. the system then performs this sql query: select .....

Consider tests:
• boss test: is your boss happy if you do this use case the whole day?
• elementary business process: add business value
• size test: a use case is seldom a single step

Contents:
• actors
• trigger
• preconsitions
• postconditions
• priority
• level: user-goal/sub-function/summary
• frequency
• type: interactive/batch/interface
• flow (basic flow, alternative flow, error handling flow): what the user does & system response, not how/why
• data dictionary (e.g. what the user enters in the UI):
   o field name
   o type (input,output)
   o required y/n
   o format: Numeric, texts, y/n, enums
   o validation
• special requests (e.g. browsers & resolutions, availability)
• storyboard: to show user expectation of system behaviour e.g. GUI information presented to the user/entered by users, actions/requests which users can perform, screenshots

If I forget something please comments :)

Reference:
Applying UML and Patterns by Larman