Annex B (informative) Use cases ToC Previous

B.7 Read parameters ToC Previous Next

B.7.1 Use case: Read offline data ToC Previous Next

Use Case Read offline parameters  
Description A software or user requests device parameter (the last set values) from a DTM. The OPC UA client collects this information by reading device parameter from the offline set provided according to the FDT OPC UA information model.  
Stakeholder    
Preconditions Device node is available in OPC UA Server and the Client already knows the ParameterIds of the Parameters to read (may have been retrieved according to use case B4.2).  
Post conditions Client knows the current value of device parameters  
Actors Engineer, Expert, Observer, Operator  
Trigger Whenever the data is needed  
Frequency    
Description    
  Step Action
  Preparation The OPC Client selects the respective device node and the parameter set of the device.
  1 OPC Client executes Read-Service (one or multiple times) with the list of identifiers for the respective device parameters (list of ParameterIds) and the list of AttributeIds for Value and (at least once) for DateType.
  2 OPC Server retrieves the requested attributes (e.g. value) of the parameter which are specified in the Read-Request from the DTM (instance data set) and returns them to the client.
  5 OPC Client displays the parameter value (or uses it otherwise).
Exceptions Step 1, The specified parameter does not exist in the device.  
Requirements    
Notes    
Open Issues    

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