Figure 13 depicts the main ObjectTypes of this specification and their relationships. The drawing is not intended to be complete. For the sake of simplicity only a few components and relations were captured so as to give a rough idea of the overall structure of the IEC 61131-3 Information Model.
Figure 13 – OPC UA IEC 611313 ObjectTypes Overview
The boxes in this drawing show the ObjectTypes used in this specification as well as some elements from other specifications that help understand the overall context. The upper grey box shows the OPC UA core ObjectTypes from which the OPC UA Device Integration Types are derived. The Device Integration model and its Types in the second level are used as base for the IEC 61131-3 ObjectTypes. The grey box in the third level shows the IEC 61131-3 ObjectTypes that this specification introduces. The components of those ObjectTypes are illustrated only in an abstract way in this overall picture. The grey box in the lowest level represents examples of sub types defined by vendors or Controller programmers.
Typically, the components of an ObjectType are fixed and can be extended by subtyping. However, since each Object of an ObjectType can be extended with additional components, this specification allows extending the standard ObjectTypes defined in this document with additional components. Thereby, it is possible to express the additional information in the type definition that would already be contained in each Object. Some ObjectTypes already provide entry points for server specific extensions. However, it is not allowed to restrict the components of the standard ObjectTypes defined in this specification. An example of extending the ObjectTypes is putting the standard Property NodeVersion defined in OPC 10000-3 into the BaseObjectType, stating that each Object of the server will provide a NodeVersion.
It is not the objective to map all IEC 61131-3 constraints to the OPC UA Information Model, but to define an OPC UA Information Model which is capable to hold at least all possible data of one or more IEC 61131-3 compliant Ctrl Configurations.
A Ctrl Configuration compliant to IEC 61131-3 represents the special case of a complete engineered Controller with an OPC UA server providing access to all data of one or more IEC 61131-3 compliant Ctrl Configurations. In general, an OPC UA server may provide incomplete Ctrl Configurations, e.g. during the engineering process or because not all data shall be accessed from outside.
Examples for Object and Variable instances of the vendor or controller programmer specific types are shown in Figure 14. The Root and the Objects Folder are Nodes defined by OPC 10000-5. The Objects Folder is the main entry point for Object instances.
Figure 14 – OPC UA IEC 611313 Object Instance Example