Parallel (Combined Fragment)   A parallel interaction operator (signified by the value of par) defines a combined fragment where the messages contained in the operands can be interleaved. It thus defines the set of traces that can occur at the same time or overlap with each other with respect to time.

Explanation

A parallel operator is a way of expressing that a number of traces can occur at the same time or be interleaved with each other. This is effectively saying that the traces do not depend on each other or affect each other. The traces that can be interleaved with each other are placed in one or more operands, and as long as the order of traces within each operand is honored the traces from different operands can be interleaved in any way. In our everyday lives this concept occurs regularly. For example when preparing for a trip there are many things that need to be readied and typically a number of people perform different tasks at the same time to prepare for the trip. An individual group of tasks may be required to occur in a sequence but a number of sets of task can all overlap saving time. At a programming level this could be represented by a number of threads or processes running concurrently.

Related Entries

Region (Combined Fragment)  Graphically Similar A combined fragment with an operator of critical region (region) is related to a combined fragment with an operator of parallel (par) because they are often used together. The parallel operator defines a number of operands that can be interleaved (overlapping in time) and the critical region is used to define a set of traces that must be executed atomically within the context of the lifelines that are enclosed within the fragment.