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== How Live Values work == Live values are special properties without a value that is persisted in the database. Instead, they get their current value frequently from a live value server, including a measurement quality indicator and a read time stamp, among other details. Live values can be used to display trends and current values (e.g., sensor values) from dynamic sources like process control systems (e.g., via OPC-UA). In {{UBIK}}, live value properties are defined by a special kind of [[MetaProperty]], a live value meta property. So, if you want to add a live value to a {{UBIK}} object, you first need to add such a meta property to the meta class of the object in question. You can get such a live value meta property from creating an instance of the [[MetaClass]] ''LIVEVALUE_METAPROPERTY''. This way, for example, you could define a property "temperature" on a meta class "cooling unit".  So, following this example, how do individual "cooling unit" instances know their specific "temperature" values? An individual live value property holds the answer: It actually ''has'' a persisted value - a reference to a so-called live value data point. Such a data point knows a live value server (providing access to a process control system for example), and an identifier of (or path to) a dynamic variable, e.g. representing a specific temperature sensor in the process control system. This means, for a specific "cooling unit" instance, we want to configure the correct live value data point as a value of the "temperature" live value property. Hence, we require a live value data point and a live value server. There is a {{UBIK}} plugin UBIK.Interface.Module.OPCUA which we can use for getting those. That module implements a specific kind of live value server, namely the OPC-UA live value server. It is represented by a meta class ''OPC_SERVER'', and instances thereof can be used to configure a connection to a specific OPC server. Similarly, there is a meta class ''OPC_DATAPOINT'' representing variable configurations. We want to have a data point instance with a link to a server instance (and a path to the variable we need). This data point instance must be set on the "temperature" property in our example. With the UBIK.Interface.Module.OPCUA plugin, {{UBIK}} will detect that there is a live value server and it will host a live value data service, supplying our "cooling unit" objects with their current "temperature" values.  ==Implementing Live Values in {{UBIK}} Studio==

# Navigate to the [[MetaClass]] ''OPC_SERVER OPC'' via the ''[[Class Browser]]''.<br/> [[File:OPCServer.PNG|330 px|border]]

# Navigate to the [[MetaClass]] ''OPC_DATAPOINT OPC'' via the ''[[Class Browser]]''.<br/> [[File:OPCDATAPOINT.PNG|330 px|border]]# Add a new instance (OPC Datapoint) to the [[MetaClass]] by using the [[Bulk Editor]]. Configure the correct path to the OPC variable represented by this datapoint. As ''REF_OPC_SERVER'' take the server created before in step 2.<br/> [[File:OPCDatapointInstance.PNG|770 px|border]]

#Add a new instance (Live Value MetaProperty) to the [[MetaClass]] by using the [[Bulk Editor]].#Add the newly created ''Live Value MetaProperty'', from step 6, to the ''Metaclass'' where you want to have the live Values to bee shown. #Add the created Datapoint from step 4 to an instance of the above ''Metaclass'' to which it concerns. <br/> [[File:AddDatapoint.PNG|770 px|border]]

*[[HowTo:Add a MetaProperty to a MetaClass]]