Explain of Interaction Operators in UML?

来源于：EA 中的 Interaction Operators Enterprise Architect User Guide

Operator	Action
alt	Divide up interaction fragments based on Boolean conditions.
opt	Enclose an optional fragment of interaction.
par	Indicate that operands operate in parallel.
loop	Indicate that the operand repeats a number of times, as specified by interaction constraints.
critical	Indicate a sequence that cannot be interrupted by other processing.
neg	Assert that a fragment is invalid, and implies that all other interaction is valid.
assert	Specify the only valid fragment to occur. This operator is often enclosed within a consider or ignore operand.
strict	Indicate that the behaviors of the operands must be processed in strict sequence.
seq	Indicate that the Combined Fragment is weakly sequenced. This means that the ordering within operands is maintained, but the ordering between operands is undefined, so long as an event occurrence of the first operand precedes that of the second operand, if the event occurrences are on the same lifeline.
ignore	Indicate which messages should be ignored during execution, or can appear anywhere in the execution trace.
consider	Specify which messages should be considered in the trace. This is often used to specify the resulting event occurrences with the use of an assert operator.
ref	Provide a reference to another diagram. The ref fragment is not created using the method described in the Create a Combined Fragment topic. To create a ref fragment, simply drag an existing diagram from the Project Browser onto the current diagram.

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·	Combined Fragments

·	Create a Combined Fragment

OMG UML
Specification

The OMG UML specification
(UML Superstructure
Specification, v2.1.1, p. 468-471)
states:

The semantics of a CombinedFragment is
dependent upon the interactionOperator as explained below.

Alternatives

The interactionOperator alt
designates that the CombinedFragment represents a choice of behavior. At most
one of the operands will be chosen. The chosen operand must have an explicit or
implicit guard expression that evaluates to true at this point in the
interaction. An implicit true guard is implied if the operand has no
guard.

The set of traces that defines a choice
is the union of the (guarded) traces of the operands.

An operand guarded by else
designates a guard that is the negation of the disjunction of all other guards
in the enclosing CombinedFragment.

If none of the operands has a guard
that evaluates to true, none of the operands are executed and the remainder of
the enclosing InteractionFragment is executed.

Option

The interactionOperator opt
designates that the CombinedFragment represents a choice of behavior where
either the (sole) operand happens or nothing happens. An option is semantically
equivalent to an alternative CombinedFragment where there is one operand with
non-empty content and the second operand is empty.

Break

The interactionOperator break
designates that the CombinedFragment represents a breaking scenario in the sense
that the operand is a scenario that is performed instead of the remainder of the
enclosing InteractionFragment. A break operator with a
guard is chosen when the guard is true and the rest of the enclosing Interaction
Fragment is ignored. When the guard of the break operand is false,
the break operand is ignored and the rest of the enclosing
InteractionFragment is chosen. The choice between a break operand without a
guard and the rest of the enclosing InteractionFragment is done
non-deterministically.

A CombinedFragment with
interactionOperator break should cover all
Lifelines of the enclosing InteractionFragment.

Parallel

The interactionOperator par
designates that the CombinedFragment represents a parallel merge between the
behaviors of the operands. The OccurrenceSpecifications of the different
operands can be interleaved in any way as long as the ordering imposed by each
operand as such is preserved.

A parallel merge defines a set of
traces that describes all the ways that OccurrenceSpecifications of the operands
may be interleaved without obstructing the order of the OccurrenceSpecifications
within the operand.

Weak Sequencing

The interactionOperator seq
designates that the CombinedFragment represents a weak sequencing between the
behaviors of the operands.

Weak sequencing is defined by the set
of traces with these properties:

1.	The ordering of OccurrenceSpecifications within each of the operands is maintained in the result.

2.	OccurrenceSpecifications on different lifelines from different operands may come in any order.

3.	OccurrenceSpecifications on the same lifeline from different operands are ordered such that an OccurrenceSpecification of the first operand comes before that of the second operand.

Thus weak sequencing reduces to a
parallel merge when the operands are on disjunct sets of participants. Weak
sequencing reduces to strict sequencing when the operands work on only one
participant.

Strict Sequencing

The interactionOperator strict
designates that the CombinedFragment represents a strict sequencing between the
behaviors of the operands. The semantics of strict sequencing defines a strict
ordering of the operands on the first level within the CombinedIFragment with
interactionOperator strict. Therefore
OccurrenceSpecifications within contained CombinedFragment will not directly be
compared with other OccurrenceSpecifications of the enclosing
CombinedFragment.

Negative

The interactionOperator neg
designates that the CombinedFragment represents traces that are defined to be
invalid.

The set of traces that defined a
CombinedFragment with interactionOperator negative is equal to the set of traces
given by its (sole) operand, only that this set is a set of invalid rather than
valid traces. All InteractionFragments that are different from Negative are
considered positive meaning that they describe traces that are valid and should
be possible.

Critical Region

The interactionOperator critical
designates that the CombinedFragment represents a critical region. A critical
region means that the traces of the region cannot be interleaved by other
OccurrenceSpecifications (on those Lifelines covered by the region). This means
that the region is treated atomically by the enclosing fragment when determining
the set of valid traces. Even though enclosing CombinedFragments may imply that
some OccurrenceSpecifications may interleave into the region, such as with
par-operator, this is prevented by defining a region.

Thus the set of traces of enclosing
constructs are restricted by critical regions.

Ignore / Consider

(p. 473) The interactionOperator
ignore designates that there are some message types that are not shown
within this combined fragment. These message types can be considered
insignificant and are implicitly ignored if they appear in a corresponding
execution. Alternatively one can understand ignore to mean that the
messages that are ignored can appear anywhere in the traces.

Conversely the interactionOperator
consider designates which messages should be considered within this
CombinedFragment. This is equivalent to defining every other message to be
ignored.

Assertion

The interactionOperator assert
designates that the CombinedFragment represents an assertion. The sequences of
the operand of the assertion are the only valid continuations. All other
continuations result in an invalid trace. Assertions are often combined with
Ignore or Consider.

Loop

The interactionOperator loop
designates that the CombinedFragment represents a loop. The loop
operand will be repeated a number of times.

The Guard may include a lower and an
upper number of iterations of the loop as well as a Boolean expression. The
semantics is such that a loop will iterate minimum the 'minint' number of times
(given by the iteration expression in the guard) and at most the 'maxint' number
of times. After the minimum number of iterations have executed, and the boolean
expression is false the loop will terminate. The loop construct represent a
recursive application of the seq operator where the
loop operand is sequenced after the result of earlier
iterations.

The Semantics of Gates

The gates of a CombinedFragment
represent the syntactic interface between the CombinedFragment and its
surroundings, which means the interface towards other
InteractionFragments.

The only purpose of gates is to define
the source and the target of messages.