Interaction DiagramsUML Specifies a

Interaction Diagrams
UML Specifies a number of interaction diagrams to model dynamic aspects of the system
Dynamic aspects of the system
Messages moving among objects/classes
Flow of control among objects
Sequences of events

Dynamic Diagram Types
Interaction Diagrams - Set of objects or roles and the messages that can be passed among them.
Sequence Diagrams - emphasize time ordering
Communication Diagrams - emphasize structural ordering
State Diagrams
State machine consisting of states, transitions, events and activities of an object
Activity & Swimlane Diagrams
Emphasize and show flow of control among objects


Sequence Diagrams
Describe the flow of messages, events, actions between objects

Show concurrent processes and activations
Show time sequences that are not easily depicted in other diagrams
Typically used during analysis and design to document and understand the logical flow of your system

Rules of thumb
Rarely use options,loops,alt/else
These constructs complicate a diagram and make them hard to read/interpret.
Frequently it is better to create multiple simple diagrams

Create sequence diagrams for use cases when it helps clarify and visualizae a complex flow

Remember: the goal of UML is communication and understanding

Summary
Sequence diagrams model object interactions with an emphasis on time ordering
Method call lines
Must be horizontal!
Vertical height matters! “Lower equals Later”
Label the lines
Lifeline – dotted vertical line
Execution bar – bar around lifeline when code is running
Arrows
Syncronous call (you’re waiting for a return value) – triangle arrow-head
Asyncronous call (not waiting for a return) – open arrow-head
Return call – dashed line

In class exercise
Draw a sequence diagram for:
In Beauty and the Beast kitchen items came to life. Draw a sequence diagram for making a peanut butter and jelly sandwich if the following objects are alive: knife, peanut butter jar (and peanut butter), jelly jar (and jelly), bread, plate. I may or may not want the crusts cut off. Don’t forget to open and close things like the jars, and put yourself away, cleanup, etc…