Standard precedence rules display the target dimension if the trigger dimension value or its descendants are in the navigation state. Leaf precedence rules display the target dimension only after descendants of the trigger dimension value have been selected.
There are two types of precedence rules, standard and leaf. The types differ in how the trigger dimension value is interpreted.
For the standard type, if the dimension value specified as the trigger, or any of its descendants, are in the navigation state, then the target dimension is displayed.
For the leaf type, only leaf dimension values (dimension values with no children) that are descendents of the specified trigger dimension value cause the target dimension to be displayed. The presence of the specified trigger dimension value in the navigation state does not cause the target dimension to appear. Hence, a leaf precedence rule requires that the trigger dimension value has children.
Example 10. Standard Rule Example
Color dimension with a child dimension value named
blue. We can construct a standard precedence rule
with
blue as the trigger dimension value and the
dimension
Shades of Blue as the target. Once the user drills
into
Color and selects
blue, the target dimension
Shades of Blue is displayed in the user interface.
For leaf type rules, we'll examine a hierarchical dimension named Country and a second dimension named State/Province. The Country dimension looks like this:
Logically, a user should choose a country before choosing a state or province. We can use a leaf precedence rule to suppress the display of the State/Province dimension until a leaf value in the Country dimension (an actual country as opposed to a continent) has been selected. To achieve this, a leaf precedence rule is constructed with the Country dimension root as the trigger and the State/Province dimension as the target. If the user drills into Country and selects an intermediate child dimension value (North America or Europe), the target dimension State/Province is not displayed. However, once the user has selected a leaf value from the Country dimension (United States, Canada, Mexico, England, Spain, or Italy) the State/Province dimension appears.
