This special input field type may be used when there are attributes that are hierarchically related in a parent-child relationship. For example, when the possible values of one attribute depend upon the value selected for the parent attribute. Location-related attributes, such as Continent, Country, Region and City are typical examples of where this type of input field may be used.
The UI displays a selectable drop-down list showing the available values for the first-level attribute. A range of values are displayed and the remainder can be accessed by scrolling up or down the list. Do the following:
- Click a first-level attribute value to select it.
A new drop-down list opens, which displays the appropriate second-level attribute values that are associated with the selected first-level value.
- Click a second-level attribute value to select it.
A new drop-down list opens, which displays the appropriate third-level attribute values that are associated with the selected second-level value.
- Repeat the above steps until attribute values have been selected for all levels of the drill down hierarchy.
Only one value can be selected at a time for each level, in this type of input field.
For a geographic location-related condition:
- The first-level drop-down list displays the continents: North America, South America, Africa, Europe, Asia and Australia.
- If Europe is selected, a second-level drop-down list displays the countries: Spain, France, Italy, Portugal, Germany, Netherlands, Sweden, Norway and so on.
- If Italy is selected, a third-level drop-down list displays the regions: Piedmont, Lombardy, Tuscany and so on.
- If Lombardy is selected, a fourth-level drop-down list displays the cities: Milan, Bergamo, Monza and so on.