Software Engineering I
Nov. 1, 2013 Notes

Interaction and sequence diagrams

1. Sequence Diagrams

  - Covered using previous notes

2. Communication Diagrams

  - Shows several objects working together
  - Similar to an object diagram, but shows communication as links instead of
    associations
  - Similar to sequence diagram, too

  +--------------+ 1: Create  +-------------+ 2:addToSchedule +---------+
  |:CourseSection| ---------> |:Registration| --------------> |:Student |
  |--------------|------------|-------------|-----------------|-------- |
  +--------------+ <--------  +-------------+                 +---------+
              3: addToRegistrationList

Communication Links
  - Exist between two objects whenever it is possible to send a message from
    one to the other
  Made possible:
  - By associations
  - Also by receiving object stored in a local variable of the sending method
    which is tagged with the local object
  - Also if a reference to the receiving object has been received as a
    parameter of an earlier message to the senter (tagged with <<parameter>>)
  - Or if the receiving object is global (tagged with <<global>>)
  - Or when objects communicate over a network (<<network>>)

Use sequence diagrams when:
  - Reader needs to see the order in which messages occur
  - Building an interaction model for a use case and you need to decide which
    steps to show
  - Showing details of messages
  - Need to show loops, optional sequences, etc.

Use communication diagrams when:
  - You are deriving interaction diagrams from a class diagram

  Do so because

  - They are the same as the object diagram, except they include communication
    links

  - They help to validate the class diagram

State diagrams
  - Used to express dynamic information about a system

  - We try to start only one state diagram in each top level diagram

  - Starting state is represented by a black dot (a * these text diagrams)

  - Ending state is represented by a black dot enclosed in a circle ( a (*) in
    these text diagrams)

  Example: Tic Tac Toe

          +----------+
  * --->  | X Turn   |-----------> (*) X Wins
          +----------+------+
              |   ^         |      
              |   |         +----> (*) Tie
              V   |         |
          +----------+------+
          | O Turn   |------------>(*) O Wins
          +----------+

  - Transitions may be named to indicate how they occur