B.6 StateMachine Extensions for ChoiceStates and Guards

B.6.5 ExpressionGuardVariableType

The ExpressionGuardVariableType provides, in addition to the human-readable semantic from its GuardVariableType, a machine interpretable representation on the semantic.

The GuardVariableType is formally defined in Table B.21.

Table B.21 – ExpressionGuardVariableType Definition

Attribute	Value
BrowseName	ExpressionGuardVariableType
DataType	LocalizedText
ValueRank	−1 (−1 = Scalar)
IsAbstract	False
References	Node Class	BrowseName	DataType	TypeDefinition	Modelling Rule
Subtype of the GuardVariableType defined in B.6.4.
HasProperty	Variable	Expression	ContentFilter	PropertyType	Mandatory

The mandatory Property Expression provides a ContentFilter, that shall be evaluated on the Object the StateMachine belongs to. This is a machine-readable semantic of the Guard. If the ContentFilter evaluates to “True”, the Guard is “True”, otherwise the Guard is “False”.

The ContentFilter for ExpressionGuardVariableType is restricted to basic operators (see OPC OPC 10000-4 for details).

The ContentFilter can reference any Variables defined on the StateMachineType and are validated on the instance of the StateMachine. If the definition of the Variable is not owned directly by the StateMachine but for example some other type, the StateMachine instance shall reference that Variable.