A Combined Fragment reflects one or more aspects of interaction (called interaction operands) controlled by an interaction operator, with corresponding boolean conditions known as interaction constraints. The Fragment displays as a transparent window, divided by horizontal lines for each operand.
This Sequence diagram illustrates the use of Combined Fragments in modeling a simplified purchasing process. A loop fragment represents iteration through an unknown number of items for purchase, after which the cashier requests payment. An alternative fragment represents the payment options, the fragment being divided to show the two operands cash and credit card. After the fragment completes its trace, the cashier gives a receipt to the customer, under the fulfilled condition that payment requirements were met.
The order of interaction fragment conditions can be changed directly on the diagram:
- Select an interaction fragment with more than one condition defined; up and down arrows appear on the right hand side of the each condition.
- Click on the appropriate arrow to change the order.
OMG UML Specification
The OMG UML specification (UML Superstructure Specification, v2.1.1, p.467) states:
A combined fragment defines an expression of interaction fragments. A combined fragment is defined by an interaction operator and corresponding interaction operands. Through the use of CombinedFragments the user will be able to describe a number of traces in a compact and concise manner.