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From your domain model I can not see the relation between Pakket and Hoofdproces and Netwerk. It seems that Service is the key because a Hoofdproces can have multiple Services and Network also seems to have multiple services. So the selection list should only give all the services that are connected to both. I have not played with the Predifined filter app but that feat might already be out of reach. You could use a datasource microflow to retrieve all the services based on both selections. But again I can not see your complete domain model so I might be wrong here. Could you tell a bit more about how the enduser does it selection proces?