1 © Wolfgang Pelz 2000-04UML2 UML Part Two. 2 © Wolfgang Pelz 2000-04UML2 Chapters Four & Twelve Interaction Diagrams

© Wolfgang Pelz 2000-04UML2 1

UMLPart Two


Chapters Four & TwelveInteraction Diagrams


Interaction Diagrams

• models that describe how groups of objects interact (collaborate)

• class and use case diagrams are useful at capturing the structural nature of a system design in a generalized way

• interaction diagrams capture dynamic behavior applicable to timing or sequencing requirements


Use Case & Interaction Diagrams• scenario - a specific instance of a use case, that is,

a particular path through system functionality• a single use case represents many related yet

distinctly different scenarios• typically, an interaction diagram captures the

behavior of a single scenario• Two forms of interactive diagrams: sequence and

collaboration/communication


Sequence• boxes at the top are participants (objects);• vertical lines are time lines; • horizontal directed lines are messages;• unless specifically noted, only sequence (location

on the time line) is important, not exact times• an activation rectangle in the lifeline indicates a

focus of control (activation) during which an object is performing an action, either directly or through another object


Notation (UML 1)


Sequence Diagram Example


Some Elaborations• Usually objects have concurrent life spans so they

are aligned at the diagram’s top.• If an object is created, its lifeline starts with the

receipt of a << create >> message.• Destruction can be explicitly noted with X.• Sequence diagrams are good at visualization of

how objects interact, but not good at showing details of algorithms, such as loops.


Another Sequence Example


Some More Elaborations• Messages are function calls in traditional programming and events in

event-driven programming.• Messages may carry parameters.• A dished line indicates a return, used to carry a return message or just

indicate the end of a group of sub-actions. • Self-call: sending messages to one self (message lines direct back to

the same life line)• Found messages: messages not originated from any participants.• Synchronous messages: messages return only when done, block the

flow of execution, no more messages from the same participant until a synchronous message is done.

• Asynchronous message: messages returns immediately, do not block the flow of execution.

• Guards are conditional expressions in square.


… and Another


alternatives in Sequence Diagrams


Time Constraints


Some More Elaborations

• Centralized control: one participants doing all the processing (traditional sequential programming).

• Distributed control: processing is split among many participants (OOP and event-driven).


Notations (UML 2)

• A participant was just an object in UML 1, but can be more than that (e.g. a group of objects) in UML 2.

• No more underline below the name in UML 2.

• : needs to be there with the class name in UML 2.

aParticipant:Class :ClassaParticipant


Interaction Frames

• New in UML2• Notations for loops, conditions and other

detail algorithms.• Common operators for Interactive Frames:

alt (alternative), opt (optional), par (parallel), loop (loop), region (critical region), neg (negative), ref (reference), sd (sequence diagram).



Collaboration (UML 1.x)Communication (UML 2.x)

– an interaction diagram that utilizes message numbering instead of a time line; emphasizes structural organization of objects that send and receive messages


Sequence Example (again)


Corresponding Collaboration Diagram


Which to Use?

• Choose sequence diagram when only the sequence of events needs to be shown and collaboration among the objects are priority.

• Choose a collaboration/communication diagram when the objects and their links facilitate understanding the interactions (you don’t have to put all objects at the top and make the lines all vertical or horizontal).

• Collaboration diagrams have relatively fixed notation and numbering scheme.


Links and Messages


Parameters and Return Values


Iteration and messages to “this”


Message Sequencing


Threads and Mutual Exclusion

• Letters in the numbering indicate different threads of control.

• Threads can be mutual exclusive if they are guarded by exclusive conditions.


Mutually Exclusive Paths


Sequence Diagram


Corresponding Collaboration Diagram


Another Collaboration Diagram


Exercise

• Draw the sequence diagram corresponding to the previous collaboration diagram


Making a Collaboration/Communication Diagram

• create a separate diagram for each system operation under development

• if the diagram doesn’t fit on an ordinary sheet of letter paper (A size), split into small diagrams

• Flat numbering (1,2,3..)is easy to keep track. Nested numbering (1.1.1.2.3.1, 1.1.1.2.2.4) can be confusing.

• use design by contract and use case descriptions to design a system of collaborating objects


Other Notations

• {tagged value} - in a class - a property either predefined or defined by the user to hold additional information about elements

• {constraint} - outside a class - applied to the role of the link

• active object - executes concurrently with its own thread of control

Documents

1 © Wolfgang Pelz 2000-04UML2 UML Part Two. 2 © Wolfgang Pelz 2000-04UML2 Chapters Four & Twelve Interaction Diagrams