If you want to filter objects across various feature classes, you will need projections.
For example: Filter all trenches that contain ducts of a certain duct type
1. Open the Duct form and filter for a duct type.
2. Right-click on the form to open the context menu and start the projection.
3. Start the projection from the duct to the trench–duct assignment.
4. The form for the trench–duct assignment is opened.
5. Right-click on the form to open the context menu and start the projection to the trench.
6. The trench form is opened with all trenches in the filter that contain a duct of this type.
Additionally, there may also be ducts of another type in this trench!
After filtering for a specific duct type in the duct form (see point 2), a named projection can also be accessed directly.
The trench form immediately opens with all trenches of the desired duct type in the filter.