Potentially, not only one ObjectType needs to be defined, but many. In this case, consider creating base ObjectTypes for common semantics and substructures.

On the other hand, it is not practical to have a very deep type hierarchy with many levels. In addition OPC UA only supports single inheritance (multiple inheritance is not supported), thus an ObjectType can be derived from only one supertype so the type hierarchy can only be organized by one aspect.

If additional aspects need to be added, composition must be used. Composition can be either done by:

• an AddIn (see OPC 10000-3), having an Object as substructure defined by an ObjectType providing a standardized BrowseName (DefaultInstanceBrowseName) and adding the aspect as defined by the AddIn-ObjectType or by
• an Interface (see OPC 10000-3), defining a substructure that is directly deployed (without grouping Object) on the ObjectType.

Composition allows definition of an aspect that can be deployed on various places in the type hierarchy, or even only on specific instances.

Therefore, subtyping should be used to refine the main characteristic of Objects of the ObjectType, and additional aspects should be defined by composition.

For example, the type hierarchy may define different types of devices (SensorType as common base type and derived a TemperatureSensorType, FlowSensorType, etc.) whereas additional aspects like the capability to lock an Object are defined by AddIns or Interfaces and added to the types.

However, even the above-mentioned example can lead to problems without multiple inheritance, as a device may support measuring temperature and flow. In this case, also the characteristic to measure a temperature and a flow should be modelled by composition (see PA-DIM for an example).