The Default Model Structure window shows the decision tree that determines what deterioration model to use for a particular type of road. "Type of road" means not only the type of road and how the road section is constructed, but also the condition attributes associated with that road section. Decision trees consist of parent nodes, child nodes, and the branches between them. The nodes are shown as boxes and the branches are the lines connecting the boxes. A parent node requires a user-selected decision variable and user-defined values to distinguish, and branch to, the parent's child nodes. The decision variables that may be used are selected in the Perf Class Variable column in the Setup PMS Analysis Columns window.
Each node of the tree represents the point at which a decision must be made. The tree then branches depending on the result of the decision. You select what decision variable is to be used in making the decision as well as the values for that variable that cause the different branches from the node to be selected. The tree is read from left to right, with the leftmost node representing the most general and the rightmost nodes the most specific.
The decision tree configured here is used in the Performance Models window, where a deterioration model is assigned to the rightmost nodes for each condition attribute.
When you right-click a node, the system displays a shortcut menu with the common commands along with the following special command:
- Edit Decision Var Limits: This command is only available for parent nodes (that is, those that have child nodes). After selecting this command, the system displays a dialog box in which you select the decision variable and values that will be used to determine which tree branch (performance model) will be followed.
