In PubSub configuration, how to config the publisher to publish only changes on data values|OPC UA Standard|Forum|OPC Foundation

Hi, we are trying to limit the publish messages, and hoping the publisher only sends out messages when there's a change in the dataStore. 

I see there's a parameter for PublishingInterval in WriterGroupDataType, and the reference (6.2.5.2) mentions "Event based DataSets". But I'm not sure if that's the right one to go after, since we still want to publish the data value, not the event.

There's also another parameter, KeyFrameCount in DataSetWriterDataType, and the reference (6.2.3.3) mentions "For non-cyclic PublishedDataSets, like PublishedEvents, that provide event based DataSets, the value shall be 0". I'm wondering how to publish delta frame of the dataStore. I tried setting KeyFrameCount to 0, which didn't change the publisher behavior.

Hope someone here can have insight about it. Thank you very much!