Specification of Reactive Hardware/Software Systems - Electronic ...

11.4 Essential Specification Modelling 357
Sender
process
Single message flow
Message with reply flow
Continuous flow
Interrupt message flow
Interrupt with reply flow
Buffered message flow
Receiver
process
Figure 11.15: Overview of Message Flow Symbols
Single message flow
This type typically models initiative of a concurrent entity. By sending without waiting
an object can continue with its operations. Control objects can use single message flows
to activate other objects. This type of flow should be avoided for the modelling of
sequential composites.
Message flow with reply
This type typically models sequential collaboration. The sender waits until the receiver
sends a reply. Concurrency boundaries typically indicate that this type of flow must be
chosen for internally collaborating objects. In the case of concurrent objects a message
that induces a reply can be modelled by separate single message flows for initial message
and reply.
Continuous flow
This type typically models that a receiver does not have to wait for a rendezvous. The
sender is always prepared to perform a rendezvous. It has a new message available
after the acceptance of each previous message. The sender must be a concurrent object
to be able to do this.
Interrupt message flow
This type typically models a message that can interrupt the current operations of an
object. The sender does not have to wait for a rendezvous. The sender can continue its
activities after sending.
Interrupt with reply flow
This type also models a message that can interrupt the current operations of an object.
The sender does not have to wait for a rendezvous to send the interrupt. The sender
must wait for a reply that must be produced by the receiver as a response to the interrupt.