System Views (SV) [Physical, Specification or Solution Views]

SV-10b Resource State Transition Description v1.2

The Resouce State Transition Description is a graphical method of describing a resource (or function) response to various events by changing its state. The diagram basically represents the sets of events to which the Resources in the Architecture will respond (by taking an action to move to a new state) as a function of its current state. Each transition specifies an event and an action.

Background:

The explicit time sequencing of functions in response to external and internal events is not fully expressed in SV-4. SV-10b can be used to describe the explicit sequencing of the functions. Alternatively, SV-10b can be used to reflect explicit sequencing of the actions internal to a single function, or the sequencing of functions with respect to a specific resource.

Usage:

Data objects:

The data in an SV-10b can include:

Representation:

Detailed Product Description:

Statechart diagrams can be unambiguously converted to structured textual rules that specify timing aspects of events and the responses to these events, with no loss of meaning. However, the graphical form of the state diagrams can often allow quick analysis of the completeness of the rule set, and detection of dead ends or missing conditions. These errors, if not detected early during the solution analysis phase, can often lead to serious behavioural errors in fielded capabilities, or to expensive correction efforts.

The Resource State Transition Description (SV-10b) relates events to resource states and describes the transition from one state to another.

SV-10b views state transitions from a resource perspective, with a focus on how the resource responds to stimuli (eg triggers and events). As in the Operational State Transition Description (OV-6b), these responses may differ depending upon the rule set or conditions that apply as well as the resource’s state at the time the stimuli is received.

The Figure below provides a template for a simple SV-10b. The black dot and incoming arrow point to initial states (usually one per diagram), while terminal states are identified by an outgoing arrow pointing to a black dot with a circle around it. States are indicated by rounded corner box icons and labelled by name or number and, optionally, any actions associated with that state. Transitions between states are indicated by one-way arrows labelled with event/action notation, which indicates an event-action pair, and semantically translates to: when an event occurs, the corresponding action is executed. This notation indicates the event that causes the transition and the ensuing action (if any) associated with the transition.


Generic State Transitions Diagram

Composing state transition provides a model of states known as a statechart.


State Chart

Depending upon the architecture project’s needs, the SV-10b may be used separately or in conjunction with the Resource Event/Trace Description (SV-10c).

SV-10b is based on the statechart diagram. A state machine is defined as “a specification that describes all possible behaviours of some dynamic model element. Behaviour is modelled as a traversal of a graph of state Nodes interconnected by one or more joined transition arcs that are triggered by the dispatching of series of event instances. During this traversal, the state machine executes a series of actions associated with various elements of the state machine.”

SV-10b relates states, events, and actions. A state and its associated action(s) specify the response of a resource or function, 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.

SV-10b can be used to describe the detailed sequencing of functions described in SV-4. However, the relationship between the actions included in SV-10b and the functions in SV-4 depends on the purposes of the Architecture and the level of abstraction used in the models. The explicit sequencing of functions in response to external and internal events is not fully expressed in SV-4. SV-10b can be used to reflect explicit sequencing of the functions, the sequencing of actions internal to a single function, or the sequencing of functions with respect to a specific resource.


Example SV-10b

States in an SV-10b View Product may be nested. This enables quite complex models to be created to represent resource behaviour.

Page version 1.2, dated 1st July 2008

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