Message Orchestration with Fragments

Many systems are inherently complex and while simple Sequence diagrams are useful for conveying an overall picture of a piece of software or an electro-mechanical device they need to be augmented to allow sophisticated models of these more complex systems to be created. One of the options for modeling complexity in message flows is the Combined Fragment. These can be used to sequence messages differently, including being able to select particular messages in certain circumstances or to execute a message a number of times. There is a set of combined fragments that can be used and their operator determines the type of fragment. Enterprise Architect supports all the operators, allowing engineers to create diagrams that can adequately describe the complex engineering systems being modeled. Fragments can be added to a diagram directly from the Interactions toolbox page and can be positioned to overlay the appropriate group of messages.

The element placed on the diagram is a generic Fragment and will need to have its operator set. This can be achieved by selecting a value for the type in the Combined Fragment property sheet.

This will change the fragment to the appropriate type and allow, for example with the alt type, to set any number of alternative conditions that will determine which message will be fired.