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InteractionUse (from Fragments ) on page 508
PartDecomposition is a description of the internal interactions of one Lifeline relative to an Interaction.
A Lifeline has a class associated as the type of the ConnectableElement that the Lifeline represents. That class may have
an internal structure and the PartDecomposition is an Interaction that describes the behavior of that internal structure relative
to the Interaction where the decomposition is referenced.
A PartDecomposition is a specialization of InteractionUse . It associates with the ConnectableElement that it decomposes.
 PartDecomposition s apply only to Parts that are Parts of Internal Structures not to Parts of Collaborations .
 Assume that within Interaction X, Lifeline L is of class C and decomposed to D. Within X there is a sequence of constructs
along L (such constructs are CombinedFragment s, InteractionUse and (plain) OccurrenceSpecifications). Then a corresponding
sequence of constructs must appear within D, matched one-to-one in the same order. i) CombinedFragment covering L are matched
with an extra-global CombinedFragment in D. ii) An InteractionUse covering L are matched with a global (i.e., covering all
Lifeline s) InteractionUse in D. iii) A plain OccurrenceSpecification on L is considered an actualGate that must be matched
by a formalGate of D.
 Assume that within Interaction X, Lifeline L is of class C and decomposed to D. Assume also that there is within X an
InteractionUse (say) U that covers L. According to the constraint above U will have a counterpart CU within D. Within the
Interaction referenced by U, L should also be decomposed, and the decomposition should reference CU. (This rule is called
commutativity of decomposition.)
Decomposition of a lifeline within one Interaction by an Interaction (owned by the type of the Lifeline ’s associated ConnectableElement ),
is interpreted exactly as an InteractionUse . The messages that go into (or go out from) the decomposed lifeline are interpreted
as actual gates that are matched by corresponding formal gates on the decomposition.
Since the decomposed Lifeline is interpreted as an InteractionUse , the semantics of a PartDecomposition is the semantics of
the Interaction referenced by the decomposition where the gates and parameters have been matched.
That a CombinedFragment is extra-global depicts that there is a CombinedFragment with the same operator covering the decomposed
Lifeline in its Interaction. The full understanding of that (higher level) CombinedFragment must be acquired through combining
the operands of the decompositions operand by operand.
PartDecomposition is designated by a referencing clause in the head of the Lifeline as can be seen in the notation section
Lifeline (from BasicInteractions , Fragments ) on page 511.
See also Figure 14.20.
If the part decomposition is denoted inline under the decomposed lifeline and the decomposition clause is the keyword strict,
this indicates that the constructs on all sub lifelines within the inline decomposition are ordered in strict sequence (see
CombinedFragment (from Fragments ) on page 487 on
the strict operator).
Extraglobal CombinedFragment s have their rectangular frame go outside the boundaries of the decomposition Interaction.
The name of an Interaction that is involved in decomposition would benefit from including in the name, the name of the
type of the Part being decomposed and the name of the Interaction originating the decomposition. This is shown in Figure
where the decomposition is called AC_UserAccess where ‘AC’ refers to ACSystem, which is the type of the Lifeline and UserAccess
is the name of the Interaction where the decomposed lifeline is contained.
In Figure 14.20 we see how
ACSystem within UserAccess is to be decomposed to AC_UserAccess, which is an Interaction owned by class ACSystem.
Figure 14.21 we see that
AC_UserAccess has global constructs that match the constructs of UserAccess covering ACSystem.
In particular we notice the extra global interaction group that goes beyond the frame of the Interaction. This construct corresponds
to a CombinedFragment of UserAccess. However, we want to indicate that the operands of extra global interaction groups are
combined one-to-one with similar extra global interaction groups of other decompositions of the same original CombinedFragment .
As a notational shorthand, decompositions can
also be shown inline. In Figure 14.21 we see that the inner
ConnectableElement s of :AccessPoint (p1 and p2) are represented by Lifeline s already on this level.
Changes from previous UML
PartDecomposition did not appear in UML 1.x.
Issue 8784 - add ReceiveOperationEvent and ReceiveSignalEvent metaclasses