In sequence diagrams, you create a combined fragment to represent a construct, such as optional, alternative, parallel, and loop. You group the messages and interaction fragments involved in the interaction in a combined fragment to compact and simplify complex interactions. Interaction fragments refer to the event occurrences, execution occurrences, interaction occurrences, and combined fragments in sequence diagrams.
You can create, move, and resize a combined fragment. When you delete a combined fragment or any of its operands, all messages and interaction fragments that are contained in the combined fragment are deleted from the model.