Annex B (informative) Use cases ToC Previous

B.4 Get list of available device parameters ToC Previous Next

B.4.2 Use case: Get attributes of a device parameter ToC Previous Next

Use Case Get attributes of a device parameter  
Description    OPC Client has the UI windows for displaying the device details information.   The UI window displays parameter names, its’ engineering units and values (if the parameter is readable).   When OPC Client displays the value of a parameter, the value is displayed according to the “display format“, which is described in the DD.If the OPC Client also has the parameter-write-function and if the parameter is writable, an UI-element for writing the value to a parameter is displayed.  
Stakeholder Mass Configuration  
Preconditions    Topology and device node are available in OPC UA Server   Device is connected to the OPC UA Server.   OPC Client gets the parameter list of a device from OPC Server.To display the parameter name and its value, OPC Client tries to get the detail information of each parameter.  
Post conditions    On the OPC client, user can see the parameter names, and can see the detail information for each parameter.    Detail Information of parameter:the data type, the label name, the minimum value, the maximum value, the engineering units, writable, readable, the enumeration list, the display format, the edit format.  
Actors Engineer, Expert, Observer, Plant Asset Manager  
Trigger Whenever a user needs the attributes of parameters for further access.  
  Step Action
  1 OPC Client requests to get the attributes of a parameter of a device to OPC Server.
  2 OPC Server gets the attributes of the parameter which is specified by OPC Client from the device DTM.
  3 OPC Client displays the parameter name to use the label name, and the engineering units.
Exceptions Step 1, The specified parameter does not exist in the device.  
Notes    To use the attributes of a device parameter which is gotten by this use case, OPC Client can work as follows.   [For read parameter]   OPC Client can recognize a parameter is readable or not, and then OPC Client gets the value of the parameter via OPC Server from the device.   OPC Client displays the corresponding label with the value if the data type of a parameter is the enumeration, otherwise (if the data type is not the enumeration) OPC Client displays the value according to the “display format“.   [For write parameter]OPC Client can recognize a parameter is writable or not, and then OPC Client can check the entered value whether the data type, and the minimum value and the maximum value of the entered value are correct or not when user tries to write a value to a parameter.  
Open Issues    

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