display IF a record is selected

[JohnLute]

I have a subform that functions as a bill of material. For example 1
"Finished Good" with many "Resources". The subform contains a "Facility"
subform that records the Facility(s) where a Resource may be used. The
Facility subform contains a "Line" subform that records the Production
Line(s) where a Resource may be used at a given Facility. This results in
records accordingly:

[Finished Good] 12345 > [Resource] 812345 > [Facility] 01 > [Line] 16

What I'd like to do is code the field [Line] so that when it's selected it
will display only the Line ID's relative to the record in [Facility]. Here
are the two subform fields:

txtFacilityID
SELECT tblFacilities.txtFacilityID, tblFacilities.FacilityName,
tblFacilities.City, tblFacilities.StateOrProvince FROM tblFacilities ORDER BY
tblFacilities.txtFacilityID;

LineID
SELECT tblFacilitiesLineIDs.LineID, tblFacilitiesLineIDs.Description,
tblFacilitiesLineIDs.txtFacilityID, tblFacilities.FacilityName,
tblFacilities.City, tblFacilities.StateOrProvince FROM tblFacilities INNER
JOIN tblFacilitiesLineIDs ON tblFacilities.txtFacilityID =
tblFacilitiesLineIDs.txtFacilityID;

I assume that I need to code LineID's Before Update Event...?

Thanks for your help!