OCUP2F 07 Sequence Diagram

Module 7. Sequence Diagram⌘

Interactions are units of behavior of an enclosing Classifier.
Interactions focus on the passing of information with Messages between the Connectable Elements of the Classifier.
4 interaction diagrams in UML 2.5:
- Sequence diagrams - sequence in which messages are exchanged
- Communication diagrams - relationship between the participants
- Timing diagrams - state changes of the participants relative to the time
- Interaction overview diagrams - order of interactions in an activity-like notation

Participants are represented by lifeline - a rectangle and a dashed line
Messages are represented by arrows between lifelines
Lifeline describes the time-line for a process, where time increases down the page
The entire diagram represents one interaction

Connectable Element

a set of instances
can be considered as objects of the specified type
lifelines (participants) represent connectable elements (properties)
If the referenced part has a multiplicity > 1, then the lifeline may have selector that specifies which particular part is represented by this lifeline

Occurrence Specification represents a moment in time at the beginning or end of a message or at the beginning or end of an execution.
The semantics of an Interaction is given as a trace (a sequence of event occurrences).

Specification of the execution of a unit of behavior within the lifeline.
Sending and receiving messages determine start and end of execution specification.

Synchronous message (filled arrowhead):
- caller waits until called behavior terminates
- reply message is represented by dashed line with either an open or filled arrow head
Asynchronous message (open arrowhead):
- caller doesn't wait but continues after call, no reply
Found message (open arrowhead originating from a filled circle):
- receiver known, sender not known
Lost message (open arrowhead pointing to a filled circle)
- sender known, receiver not known
Create message (dashed line with open arrowhead pointing to header of lifeline):
- new lifeline is created at this point in the diagram
Delete message (open arrowhead):
- object destruction, stop (destruction of an object is represented by a cross on the lifeline)

Sequence of event occurrences (trace) is defined by <eventoccurrence1, eventoccurrence2, ...,eventoccurrence-n>
send event is denoted by an exclamation mark (!p)
receive event is denoted by question mark (?p)
A valid sequence for the interaction: < !p, ?p, !q, ?q >
It's not the only valid sequence!

Send event before receive event
The order of events along one lifeline is relevant.
The position of one event relative to an event on another lifeline is insignificant.