Sequence Diagrams

1
Sequence Diagrams

• 4-10-2002

2
Opening Discussion

• You will be presenting on the 24th. That gives
  you 2 more weeks to try to get a prototype
  implementation. The real key for the
  implementation is that it is going to tell you
  where your design needs work.
• Your presentation is going to focus primarily on
  your design, but the more implementation you
  have, the better.

3
Back to UML

• Today we are going to get back to talking about
  UML diagrams. We have discussed the Use Case
  diagrams for helping up with the analysis to
  figure out what users will be using various parts
  of our system and for what. We have also
  discussed class diagrams which show us the
  general layout of an object oriented design and
  help us see how pieces of code fit together.

4
Sequence Diagrams

• Today we are going to look briefly at Sequence
  Diagrams These diagrams are used for individual
  methods to show us the passing of messages in a
  method.
• In particular they show us the timing of how the
  different messages are passed (or methods are
  called if you prefer the terminology).

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Layout of a Sequence Diagram

• The basic layout of a sequence diagram has the
  objects that receive messages listed along the
  top. Often the objects are denoted by just a
  class name.
• The vertical axis has time advancing as you go
  down so the beginning of the method is at the top
  and the end is at the bottom. There is a time
  line down from each object as well.

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Calling of Methods

• When a message is passed to an object (a method
  invoked), we draw an arrow from the current
  method to a method on the line of that object.
  The arrow is labeled with the method name.
• Boxes along the line represent the method
  execution. They are typically given a size that
  corresponds to how long their execution should
  take. Returns are implicit.

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Asynchronous Messages

• If you have code that spawns threads so that
  messages can be processed in parallel you can
  denote that in a Sequence diagram with a half
  arrow.
• TogetherSoft has quite a few different options
  for the types of messages being passed. It will
  also generate Sequence diagrams from code.
  TogetherSoft shows an actor to initiate the call
  as well.

8
Look at Snipes Code

• To help show the flexibility of the design of the
  project, I am also implementing a client/server
  pair for the game Snipes. Snipes used to ship
  with all Novell LANs. In some ways it was the
  first 3rd person, multi-player shooter.
• Im not very far yet, but I will continue with it
  and on Friday at 230pm I will work on it as part
  of a series on Java I have been doing.

9
Meet in Groups

• As time allows Id like you to break apart into
  your groups and discuss your projects. You
  should be turning in UML diagrams and group
  evaluations for them to me today. Your final
  presentations are in 2 weeks.