OPC UA Source System: Structures Tab

Use

You use this tab to select structured data types. A structured data type describes a data type that consists of several components. The component in the OPC UA environment corresponds to a field.

You can use structured data types as follows:

• In conjunction with retrieve and store queries (see: Query Destination System.)

• As subscription items

For more information about functional limitations, see Functional Limitations.

In order that structured data types can be used, the OPC UA agent instance needs to request data type information from the server at runtime. This task is only performed semiautomatically in SAP PCo in the current release. It is technically possible to request this information if required, in other words, whenever the PCo OPC UA agent instance wants to store or retrieve at runtime. However, because the PCo UA agent instance communicates with an OPC UA server using mass queries, it doesn’t make sense to check after such a query if all the data types have been recognized correctly, because this would lead to client-server roundtrips.

Instead, at design time you need to specify which structured data types you want to be used at runtime. You do this using the browse dialogs on the Structures tab. The type information is loaded for the data types that you select here after the agent instance has started and can be used at runtime.

Activating the Function

To activate the function, you select the checkbox Support for Structured Data Types on the Session tab (see also: OPC UA Source System: Session Tab).

Procedure

1. Choose the Add New Structured Data Type pushbutton.

   The Browse OPC UA Structures dialog box appears in which you can browse the address space of the server. There are two tabs:

   • Variables tab

     You can navigate here to a node that you want to read at runtime or to which you want to write at runtime.

   • Types tab

2. If you select a node with the node class Variable, the following information is displayed for the selected node in the lower part of the dialog box:

   • Node ID

     The ID of the node is displayed. The ID consists of ID type, namespace URI, and identifier.

   • ID of the relevant data type

   • Data type

     The data type is displayed in the status bar. Here you can see which data type the node is:

     • Simple data type, for example, string, double, or integer

     • Object data type

     • Structured data type

   You can only select nodes here that correspond to an instance of a structured data type. From a technical viewpoint, this means that the data type structure is derived from the node with the ID ns=0; i=22. Data types from the namespace of the OPC Foundation (http://opcfoundation.org/UA/, this is the namespace with the index 0) should already be known and cannot therefore be selected.

3. Hierarchies of structured data types and abstract structured data types are supported. However, you must explicitly select all concrete data types that can occur at runtime. (See: Example: Configure Derived Data Types.)

4. Select a node and confirm with OK that you want the data type that belongs to this node to be used at runtime.

   The node is added to the list of data types that are to be used.

5. Instead of selecting the data type using an instance, you can also select the type directly on the Types tab. To do so, switch to the Types tab.

   This tab displays the type hierarchy on the OPC UA server below the structure data type. The details for the node type are displayed in the lower area of the dialog box.

6. Browse the tree on the Types tab until you find the data type you want. Select it and choose OK.

7. Once you have selected the types, you can display your selection in a hierarchical view on the Structures tab by choosing Show Structured Data Types Hierarchy.

   Your chosen data types are selected.

8. If you want to use structured OPC UA data types, which you have configured here, in a tag-based notification, you can import the OPC UA data types into the PCo data type repository and thereby generate the PCo data types that correspond to the OPC UA data types. (See also: Import OPC UA Data Types into the PCo Data Type Repository.)