Use Advanced Combobox (MasterBox) controls to filter a combo box. For example, instead of selecting a street in a long list showing all streets of all cities, select the city first. Then select the street from a shorter list.
In a feature class form, the advanced combo box is controlled by the combo box. For example, the advanced combo box has no relation to any attribute of the form. It is related only to the combo box. If you browse, you will always see the corresponding values, such as city, district, or street. If you change any of these values, the corresponding location is emptied.
Set the properties in a Master Box properties window. Click 
in any master box property row to open this window.
Advanced Combobox Properties Example
- Detail Control: FID_STREET
- Master Table: LM_CITY
- Detail Table:
- Master Attribute: FID
- Detail Attribute: FID_CITY
- Display Attributes: NAME
- OrderBy: NAME
Example: Multi-relation Advanced Combobox: City ->District -> Street ->Location
Target: To assign a location (house number) to a building with the help of a combo box (BUILDING.FID_LOCATION <- LM_LOCATION.FID).
The user does not want to select the location from the table LM_LOCATION. He wants to select the city first, then the district and street, and finally the location. Each drop down list will contain only the pre-selected items.
In this example, the user can restrict the selection of the location by city, district, and street.
The following relations exist: There are several cities; every city has several districts and every district has streets and every street has locations (house numbers).
LM_LOCATION { FID, ..., Number, FID_STREET }
LM_STREET { FID, ..., Name, FID_DISTRICT }
LM_DISTRICT { FID, ..., Name, FID_CITY }
LM_CITY { FID, ..., Name }
PARENT_TABLE_NAME.PARENT_COLUMN_NAME
-> CHILD_TABLE_NAME.CHILD_COLUMN_NAME
LM_CITY.FID -> LM_DISTRICT.FID_CITY
LM_DISTRICT.FID -> LM_STREET.FID_DISTRICT
LM_STREET.FID -> LM_LOCATION.FID_STREET
LM_LOCATION.FID -> BUILDING.FID_LOCATION
The above relations must be defined in TB_RELATIONS. Now you can configure the master boxes for the feature class form Building. Master boxes are created for the FID_LOCADTION combo box.