A.11 Modelling guidelines

An AutomationComponent is either modelled as AML InternalElement as part of an AML InstanceHierarchy or as AML SystemUnitClass (SUC).

If the AutomationComponent is modelled as InternalElement (IE), it shall be either a direct or indirect instance of the SUC AutomationComponentType. If modelled as an SUC, it shall be a subclass of the SUC AutomationComponentType.

AutomationML does not have modelling rules, like mandatory or optional, that guide the creation of instances. Instantiating an SUC usually results in the creation of all InternalElements that are modelled as instance declarations on the type. However, since the UA modelling rules are present on the SUC of the OPC UA FX Libraries, engineering tools could do automatic postprocessing and delete the optional IEs from the type or let the user decide which optional IEs should be removed.

When making changes to an already existing AML InternalElement, two strategies can be followed:

  • Change the InternalElement directly. Here, every operation (add, change, delete) is possible as long as it does not violate a rule from the OPC UA standard. However, in these cases, the original instance is not kept.
  • Convert the InternalElement to an SUC, make the SUC a subclass of the SUC from which the InternalElement was created, and make an instance from this new SUC for further editing. This allows keeping the original InternalElement as an SUC in the type system. If this is done repeatedly, an instantiation step is followed by an SUC-conversion step, and the work history is available in the derivation chain of the modelled SUCs.

If an ObjectType, VariableType, DataType, or ReferenceType is used in an OPC UA FX Information Model that is not defined in the libraries listed in Annex B, Annex C, Annex D, and Annex E, a definition of the object type, variable type, data type, or reference type shall exist in an OPC UA FX Library, and this library shall be included in the Descriptor. The OPC UA FX AML Core Libraries are those libraries defined in this document.

For modelling of safety information for a Descriptor, the OPC UA FX AML Safety library shall be used (see Annex E).