Hi Robert,
if you go to table level, you find ties between the logged tasks/events in table POC_D_PRE_BA. The relationships between the activities are just a projection out of this.
Instead of creating your own views, you may also check our predelivered calc views in the SAP HANA Live package for EhP4. It comes bundles with HANA and you find the definition of the views here: Process Observer - SAP HANA Live for EHP4 for SAP ERP - SAP Library
Regards,
Bernd