Object-oriented modeling Sequence diagrams

1. Object-oriented modelingSequence diagrams Karolina Muszyńska Based on: S. Wrycza, B. Marcinkowski, K. Wyrzykowski „Język UML 2.0 w modelowaniu SI”

2. Object Modeling • Dynamic view – sequence diagrams • role and types of sequence diagrams • basic concepts • advanced concepts • examples

3. Sequence Diagram –role • Sequence diagram is a kind of interaction diagram, describing interactions among system classifiers in the form of sequence of messages interchanged between them during a certain period of time. • Sequence diagrams are closely related to use case scenarios as they document their functionality. • Interaction is shown on the sequence diagram in two dimensions: • Horizontal - static dimension where the system classifiers taking part in the interaction are placed • Vertical – dynamic dimension, with the time line showing chronically arranged messages

4. Sequence Diagrams –types Depending on the degree of abstraction three types of sequence diagrams can be specified: Conceptual sequence diagram – using only basic concepts, for quick and general overview of the system interactions Generic sequence diagram – is the basis for software specification and uses all available concepts; this type of diagram includes the main and all alternative scenarios of a use case and it can be used for automatic generation of program code Instance sequence diagram – a diagram describing one particular scenario of a use case; there may be several instance diagrams for one generic diagram

5. Sequence Diagrams –basic concepts Classifier – abstract category of system modeling in UML (e.g. actor, object, interface, component, package, etc.) Message – describes a control flow in the system; it determines the sequence and place of execution of operations; messages are arranged according to the sequence of their appearance – the later they occur the lower they appear on the diagram Each classifier has a lifeline that represents its life time; the “X” mark at the end of the lifeline indicates the point at which the object ceases to exist in the system The execution specification shows time period during which the classifier performs an operation (processing, calculating, communicating with other classifiers or executing complex algorithms); the execution specification is initiated with an activation and ended with deactivation.

6. Sequence Diagrams –basic concepts Classifier(actor, object, interface, package) Lifeline Message

7. Sequence Diagrams –basic concepts Activation Deactivation Execution specification

8. Sequence Diagrams –advanced concepts Types of messages Creating and destroying objects Guard conditions Combined fragments with interaction operators Interaction occurrences

9. Sequence Diagrams – advanced concepts Message types: synchronous message – passes control from the sender classifier to the receiver classifier asynchronous message – does not pass control, does not wait for an answer from the receiver, may continue processing return message – indicates control return to the sender classifier after synchronous message and may also initiate a certain operation self message – message sent by the classifier to itself resulting in calling its own operation; self message is a certain kind of iteration, which creates a nested execution specification

10. Sequence Diagrams – advanced concepts Synchronous message Asynchronous message

11. Sequence Diagrams – advanced concepts Return message Self message

12. Sequence Diagrams – advanced concepts Other message types: lost message – message sent from a known sender to an unknown receiver (temporary message) found message – message whose sender is unknown (may be an external signal, stimulus) balking message – message which will not be handled by the receiver classifier if it cannot be handled immediately timeout message – similar to balking message although sender classifier is willing to wait for handling the operation for a specified period of time

13. Sequence Diagrams – advanced concepts Creating and destroying objects: „create” stereotype message – results in creation of an object, which is situated below the primary existing classifiers, corresponding with the time of its creation „destroy” stereotype message – results in destruction of an object

14. Sequence Diagrams – advanced concepts <<Create>> message <<Destroy>> message

15. Sequence Diagrams – advanced concepts Guard condition – a criterion connected with the message, on fulfillment of which depends the execution of a specified operation. If a condition referring to a certain message is not met the operation indicated by the message is not executed. Conditions are placed in square brackets before the message name Realization of a message can be conditioned by more than one condition

16. Sequence Diagrams – advanced concepts Guarding condition

17. Sequence Diagrams – advanced concepts Combined fragment – is a logically consistent area of interaction, a part of a sequence diagram characterized by specific properties defined by the interaction operator Interaction operator – specifies the functionality realized by the combined fragment Interaction operators:

18. Sequence Diagrams – advanced concepts Selected, most common operators: alternative (alt) – means a possibility to choose only one of all presented interaction operands within the combined fragment, depending on the condition assigned to the operand option (opt ) – means that the operand within the combined fragment will occur or will be omitted, depending on the condition interruption (break) – is a abbreviated form of alt with only one defined operand and when the combined fragment is executed other interactions are ignored iteration (loop) – means repeating the operand a specified number of times

19. Sequence Diagrams – advanced concepts

20. Sequence Diagrams – advanced concepts

21. Sequence Diagrams – advanced concepts

22. Sequence Diagrams – advanced concepts

23. Sequence Diagrams – advanced concepts Interaction occurrence – is a reference to a linked interaction diagram, placed within the base diagram Interaction occurrences are especially useful in case of extensive sequence diagrams, which refer to other diagrams defined earlier Interaction occurrence can be invoked either by a message or by time factor

24. Sequence Diagrams – advanced concepts Interaction occurrence

25. Building a sequence diagram Analysis of a selected use case and its scenarios Identification of classifiers taking part in the interaction Development of conceptual sequence diagram including (identified classifiers, messages and execution specifications) Development of a generic sequence diagram on the basis of the conceptual diagram by adding advanced concepts like: different message types, conditions, combined fragments, interaction occurrences Optional development of instance sequence diagrams for a selected generic diagram