Sequence Diagrams

4-10-2002

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.

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.

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).

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.

Calling of MethodsWhen 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.

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.

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.

I’m not very far yet, but I will continue with it and on Friday at 2:30pm I will work on it as part of a series on Java I have been doing.

Meet in Groups

As time allows I’d 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.