Precedence rules: Standard and leaf

Precedence rules provide a way to delay display of dimensions until they offer a useful refinement of the navigation state. They are defined in terms of a trigger dimension value and a target dimension, where a user’s selection of trigger dimension value reveals previously unavailable target dimension to the user.

Standard and leaf precedence rules

There are two types of precedence rules, standard and leaf. The types differ in how the trigger dimension value is interpreted.

  • For standard type, if dimension value specified as trigger, or any of its descendants values are in navigation state, then target dimension is displayed.
  • For leaf type, only leaf dimension values (dimension values with no children) that are descendants of specified trigger dimension value cause 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.

Standard Rule Example

For a standard auto parts implementation, we display Make and Model dimension for a car. When user selects Make, we will display Model dimension values. We can construct a standard precedence rule with Make as trigger dimension value and Model dimension as the target. Once the user drills into Make, target dimension Model is displayed in the user interface.

Leaf Rule Example

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:

  • Country
  • North America
  • Canada
  • Mexico
  • United States
  • Europe
  • England
  • Spain
  • Italy

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.

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