title: OPC UA - Client - Milo - Best Practice - Subscription to Data Change
body: <p>I started a OPC UA project using the Milo project to create a OPC UA Client. I am still very new to OPC UA. Right now I am stuck looking for the best practice to read values from several Nodes after a data change of one specific node.</p>
  
  <p>The information model looks like this:
  <a href="http://i.stack.imgur.com/oN5Ar.png" rel="nofollow">RfidSensorType</a></p>
  
  <p>On my server i will have several objects of this RfidSensorType. The client creates a subscription on the CurrentAtTag Node to listen for data changes. </p>
  
  <p>My Question:
  When the value of CurrentAtTag is changed a callback function will be called in my client which contains the UaMonitoredItem and the DataValue of the CurrentAtTag. 
  In my application i need to process (at the same time) also the values of Station, IOLPort and CurrentValue which are changed at that moment too. 
  How can i access those values within the callback from CurrentAtTag?</p>
  
  <p>My only solution is: Using a synchronous read request within that callback
  -> Is that an legit approach?</p>
  
  <p>My Research:
  1) TriggeringService 
  I've seen that a TriggerigService exists, which monitors items will send reports only if one specific node changes it values. 
  Problem: This will call several callsbacks and noz just one..i need all the informations at the same time to further process them..</p>
  
  <p>2) Event Monitoring
  In event monitoring one can select "Event fields" which will be returned for each Event notificaiton. I am not sure if i could select the CurrentAtTag, Station, IOLPort and CurrentValue...</p>