The HasGuard ReferenceType is a concrete ReferenceType and can be used directly. It is a subtype of HasComponent.

The semantic of this ReferenceType is to point from a Transition to a Guard. The Guard indicates if the Transition can be used or not (see GuardVariableType). A Transition can only be used, if the Guard is "True". A Transition can point to several Guards. In that case, all Guards need to be "True" before the Transition can be used. If there is no Guard, the Transition can always be used (considered as if all Guards are "True").

The SourceNode of this ReferenceType shall be an Object of the ObjectType TransitionType or one of its subtypes. The TargetNode shall be a Variable of the VariableType GuardVariableType or one of its subtypes.

The representation of the HasGuard ReferenceType in the AddressSpace is specified in Table 21.

Table 21 – HasGuard ReferenceType

Attribute	Value
BrowseName	HasGuard
InverseName	GuardOf
Symmetric	False
IsAbstract	False
References		NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the HasComponent ReferenceType defined in OPC 10000-5
Conformance Units
Base Info Choice States