These properties would set automatically by PRPC when an interaction case gets created. These properties point to the current interaction-ID. The CurrentInteractionID was set in the 2 nd step of the Activity: CPMPerformDefaults which is the pyID of the interaction case. You can use refer these properties.
The CAParentID was set from the DT: CPMReferDeclarativeProperties where it will take the pyID of the primary page context and set it to the property: CAParentID.