A combined fragment is a logical grouping, represented by a rectangle, which contains conditional structures that affect the flow of messages on a Sequence diagram. You can use combined fragments to describe control and logic structures in a compact and concise manner.
A combined fragment contains Interaction Operands and is defined by an Interaction Operator. The type of combined fragment is determined by the Interaction Operator.
The Combined Fragment symbol is available on the Draw toolbar of a Sequence diagram in SysML or UML 2.5.
You may specify the Interaction Operand on the CombinedFragment tab in the Combined Fragment definition.
A Combined Fragment can also contain nested Combined Fragments or Interaction Uses containing additional conditional structures that affect the flow of messages.
Interaction Operators include:
▪seq – Weak Sequencing.
▪alt – Alternative multiple fragments, where only the one whose condition is true will execute.
▪opt – Optional: the fragment will execute only if the guard condition is true.
▪par – Parallel: each fragment will run, in parallel.
▪strict – Strict Sequencing.
▪loop – Loop: the fragment will execute over and over in a loop, with the guard condition specifying for how long.
▪critical – Critical Region.
▪neg – Negative: the fragment visualizes an invalid interaction.
