Software Engineering I
Sept 27, 2013 Notes

Last time: Use Cases

This time: More use cases, examples, extensions and generalizations

Use case: Open File

Related use cases:
Generalization of:
-open file by typing name
-open file by browsing

Steps:

1. Choose open command  <-- actor action
2. Display file open dialog <-- system response
3. Specify file name <-- actor action
4. Confirm selection <-- actor action
5. Remove dialog from display <-- system reponse


Use case: Open file by typing name

Related use cases:
Generalization: open file

Steps:
1. Choose open command <-- actor
2. Display file open dialog <-- system
3. a. Select text field <-- actor
   b. Type file name    <-- actor
4. Click open  <-- actor
5. Remove dialog from display <-- system


In class exercise:

Open file by browsing

Use case: open file that does not exist

Related use cases:
Extension of: Open file by typing name

Steps:

4. Click open <-- actor
4. a. Indicate file does not exist <-- system
   b. Correct file name <-- actor
   c. Click open <-- actor
   d. Return to 4. a. if file does not exist <-- system
5. Remove dialog from display <-- system

Use case: Browse for file (inclusion)

Steps:

1. If desired file is not found, select directory <-- actor
2. Display directory <-- system
3. Repeat 1 until file is displayed <-- actor
4. Select file <-- actor


Modeling process

  We need to choose use cases to focus on during the modeling process.

  - One or a few use cases are often indentified as _central_.

  - Ex: Airline Reservation System
      Reserve a seat on a flight

  - System can often be built around a central use case
 
  - Some use cases are high risk

    + Known problems with implementation

    + Ex: Navigation system

       - Enter navigation mode

       - Speak now

 - Some have high political/commercial value

    + Impress people

Benefits of Use Cases

  - Drive development process

  - Help define scope of system

  - Help plan development process

      # of use cases helps to indicate project size

  - Help to develop and validate requirements

  - Help to define test cases

  - Help structure manuals

Do's and Don't's 

  - Do validate use cases
  - Do investigate what might not be covered by use cases
  - Add innovative use cases

  - Don't just follow what has been done before
  - Don't add extraneous use cases

Scenarios - instances of use cases


Requirements gathering

  - Observation
  - Interviewing
  - Brainstorming
  - Prototyping

Observation

  - Read documentation, discuss requirements
  - Watch users at work (shadowing)
  - Look out for subtle, but important, details
  - Important for large systems because it helps with planning/design

Interviewing

  -plan what to do
  -interview lots of stakeholders
  -spread out over time
  -prepare questions

  -get specific details
    -determine stakeholder's vision
    -alternative ideas
    -minimum acceptable system
    -have the stakeholders draw diagrams
    -ask about other information sources