The ReferenceDescription defined in 0 keeps the simple construct of a Reference and adds a Variable to provide additional information. This approach allows to handle the References natively without the need to access the additional information. An alternative approach is described in the next section.

One modelling construct to add information to References, is to provide an intermediate Object as proxy with additional information (see Figure A.1). The approach often makes sense. For example, to provide information about the physical cable connecting two devices represented as Nodes, another Node is added representing the cable, and both device Nodes are connected to the cable Node. The disadvantage of the approach is, that a Client cannot natively follow the Reference to the target directly, but always gets to the intermediate Object first and from there to the original target. Therefore, the ReferenceDescription uses an approach, where the Reference directly connects both Nodes without the need to deal with an intermediate Object.

Figure A.1 – Refinement of References by Proxy Object

Bibliography

[1] OPC 30010, OPC UA for AutoId Devices

[2] OPC 30120, OPC UA for IO-Link Devices and IO-Link Masters

[3] OPC 10000-100, OPC Unified Architecture – Part 100: Devices

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