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110 P.-O. Siebers and F. Klügl

Table 6.8 Relevant sequence diagram components
Component Symbol Description
Lifeline Named element which represents an individual participant
in the interaction
Message From sender to receiver
Message Return message
Execution Represents a period of time in which the participant is
active
Message Self message
Loop Wrapper for representing loops (has one compartment)
Alternative Wrapper for representing alternatives (has as many
compartments as alternatives exist)

Interface DataBase
User1 User2
1: Ask for information
1.1: Ask for information
1.2: Reply
1.3: Reply

2: Ask for information
2.1: Ask for information
2.2: Reply
2.3: Reply

alt
[random (depending on archetype)]
3: Start communication
4: Reply communication

[random (depending on archetype)]
5: Start communication

6: Reply communication

Fig. 6.7 Initial sequence diagram for the use case “observe others” [drawn with Visual Paradigm]

are users and units that provide information. Users interact with information units
and with each other. Information units interact with the users and with each other.
Creating this diagram sparked a discussion if we should consider a database that
stores historic information in our model or not. It is currently not represented in the