Processes Step by Step

Model Design

Description of Behaviour (Life Cycles)

The active entities in our model are the van carrier(s) and the trucks. All trucks have the same "behaviour" in that they arrive at the terminal, queue for service by a van carrier, and finally leave the terminal again. Thus they can all be classed as one type of entity. The same holds true for the van carriers, respectively. We will represent each type of active entity by a different class of simulation process when we implement our conceptual model later.

We have identified the following types of entities:

• A van carrier is a server in our queueing system. It is a permanent entity, i.e. it is always part of the system, never entering or leaving.
• A truck requests service and can therefore be called a customer (or transaction) in our queueing system. It is a temporary entity, i.e. that it is not always present. It enters the system at some point in time, stays for a while, and then leaves again at some other point in time. In fact, there will be a constant "flow" of trucks through the system.

The second step in designing our model of the truck loading zone of a container terminal is to describe the behaviour of every type of entity. We need a clear idea of what these entities do and how they interact. So now it's your turn: Start with the van carrier and write down its tasks, then proceed with the truck. Or better still, draw a UML activity diagram depicting the life cycle of each entity type.