P5 – Resource States

The P5 Resource States View describes how Resource Types change state in response to events and other stimuli.

Concerns Addressed

• Systems Engineering.
• Safety Cases.

Background

A P5 View identifies the states a Resource Type can be, the allowable changes between those states, and the triggers that cause the state changes.

Usage

• Definition of states, events and state transitions (behavioural modelling).
• Identification of constraints.

Representation

• UML state diagram (preferred).

Detailed View Description

The P5 View relates events to Resource Type states and describes the transition from one state to another from a resource perspective, with a focus on how the Resource Type responds to stimuli (e.g. triggers and events). As with the L5, Logical States View, these responses may differ depending upon the rule set or conditions that apply, as well as the Resource Type’s state at the time the stimuli is received.

Figure 3-65 provides a template for a simple P5 view.

Figure 3-65: Simple P5 Generic State Transitions Diagram

Composing state transitions provides a model of states known as a state chart, as shown in Figure 3-66.

Figure 3-66: Example P5 State Chart

A state and its associated action(s) specify the response of a Resource Type to events. When an event occurs, the next state may vary depending on the current state (and its associated action), the event and the rule set or guard conditions. A change of state is called a transition. Each transition specifies the response based on a specific event and the current state. Actions may be associated with a given state or with the transition between states.

Figure 3-67: Example P5 View

States in the P5 View may be nested. This enables quite complex models to be created to represent resource behaviour.

Key Elements and Their Relationships

Meta-Model

The detailed meta-model and element list for P5, Resource States, is at paragraph 4.5.6.