Interfaces are ObjectTypes that represent a generic feature (functionality), assumed to be usable by different ObjectTypes or Objects. The Interface model specifies the rules and mechanisms to achieve this.

The “InterfaceTypesObject (see OPC 10000-5) has been defined so that all Interfaces of the Server are either directly or indirectly accessible browsing HierarchicalReferences starting from this Node.

Rules for the definition of Interfaces:

Rules for applying Interfaces:

If the rules cannot be fulfilled (e.g. name collisions) the ObjectType cannot apply the Interface, i.e. it shall not reference the Interface with a HasInterface Reference of a subtype.

The rules apply for each referenced Interface. As a consequence, an ObjectType cannot reference two Interfaces using the same BrowsePath for Nodes that are not similar Nodes or have TypeDefinitionNodes that are not compatible (compatible means they have either the same TypeDefinitionNode or one TypeDefinitionNode is the subtype of the other TypeDefinitionNode).

Figure 8 illustrates example Interfaces:

  • ISerializeServiceType, an Interface to convert the Object and its components into a stream of bytes.
  • ITransactionServiceType, an Interface to perform a sequence of changes to the Object as a single operation.
  • ILocationType, an Interface to specify the installation location of the Object.


Figure 8 – Examples of Interfaces

The following examples illustrate the application of these Interfaces. In Figure 9 the example Interface ILocationType is applied to the XYZ-DeviceType ObjectType. It also illustrates the overriding of Property “Address” by changing the ModellingRule from Optional to Mandatory. Figure 10 in addition shows how to use the ISerializeService Interface on the instance only. Figure 11 shows an Interface hierarchy where InstanceDeclarations of the referenced Interface and its parent type(s) are applied (the fully-inherited InstanceDeclarationHierarchy).


Figure 9 – Example: Interface application to an ObjectType


Figure 10 – Example: One Interface applied to an ObjectType another one to the instance


Figure 11 – Example: Interface Hierarchy

Clients can detect the implementation of Interfaces by filtering for the HasInterface Reference into the Browse Service request.

On instances, the Browse Service will return elements derived from an Interface together with elements of the Node’s base type. Clients can also use the TranslateBrowsePathsToNodeId Service with BrowseNames of Interface members to get the NodeId of these members directly.

In the example in Figure 10Address” with the starting node MD002 can be used to request the NodeId of this Property.

On Object instances, some Nodes of an Interface may not be available if defined with ModellingRule Optional.