The fact that it is possible to reference an interaction from
within several different sequence diagrams is much more important. This helps
avoid redundancies (i.e., several descriptions of the same interaction) and allows
you to reuse the interaction.
An interaction use is denoted with the interaction operator ref , similar to a combined
fragment. The name of the interaction is inside the fragment ( Figure 3.78 ).
There is another decomposition mechanism, in addition to the interaction use.
It allows us to decompose a single lifeline. It works like zooming into the lifeline.
The reference to the detailed sequence diagram is denoted in the header underneath
the name ( Figure 3.79 ).
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3.8.6 State Invariant
3.8 Interaction Diagrams
FIGURE 3-78
Example for an interaction use.
sd Read card
:Card :Card reader
Trigger card reset ref
ref Change protocol
Command1
Response1
sd Trigger card reset
:Card :Card reader :Card reader
RESET
opt
ATR
sd Change protocol
[Change protocol]
PTS Request
PTS Response
:Card
Defi nition
A state invariant is a constraint that refers to a lifeline, and which has to be
met at system runtime.
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