Xpath for filter based on association

I'm using the Predefined filter app and want to add a filter to my listview. I don't understand how the XPATH system works and the more I read about it the less I understand. What XPATH constraint do I need to filter a listview filled with Pakket based on Hoofdprocess and Netwerk? A servicepakket could belong to two networks and thus adding an attribute to filter it that way would not work. It'd be even more of a mess for Dienstenpakket.  
1 answers

You might want to watch this webinar: http://ww2.mendix.com/expert-webinar-deep-dive-into-xpath.html

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?