WEBDEV Concepts

Part 4: Advanced concepts 125 A collaboration diagram includes the following elements: • object : represents the different objects used. • actor : represents an element external to the system. A person, for example. • message : represents the messages exchanged between different objects. 2.8 State-transition diagram A state-transition diagram presents a sequence of states that an object goes through during its lifecycle. It describes how the states of an object or component change. A state is defined by its duration and stability. A transition represents the change from one state to another. A transition is triggered: • by an event. • automatically when no triggering event is specified. For example, the diagram below presents the different steps of a car wash: A state-transition diagram includes the following elements: • state : represents the value of the object attributes at a given time. • initial state : represents the state when the system is started. • final state : represents the state of the system at the end of the operation. • superstate : used to structure the diagram by specifying several distinction levels between the states. • history : represents the last active state of a superstate (or composite state). • entry/exit points : represent the states in a superstate. This allows you to link these states to other states that do not belong to the superstate. • transition : represents the change from one state to another. 2.9 Deployment diagram A deployment diagram shows the physical arrangement of devices (hardware/nodes) in a system as well as the relationships between the executables and these devices. For example, the diagram below represents the hardware used in a company: A deployment diagram includes the following elements: • node class : represents a class of a physical resource. For example: server, PC, printer, etc. • node instance : represents a physical resource. For example: server 3, printer 70, etc. • connection : depicts the communication path between two nodes. For example: ISDN or TCP/ IP link.