Rule Designer checks for overlaps and gaps in decision tree conditions, and indicates problems using visual cues.
If there is an error or warning in a decision tree, the 
warning symbol identifies the affected nodes and branches.
When you save the decision tree, the errors and warnings also appear in the Problems view.
A decision tree that has a checking error cannot be executed, unless you disable checking.
The rules that make up your decision tree can be checked for gaps and overlap. You can specify your checking preferences at node level and at tree level.
Gaps
Rule Designer checks that the branches in the decision tree are uninterrupted. For example, if one branch defines the interval [21 - 30] and another branch defines the interval [33 - 40], an error is generated since the interval [31 - 32] is not accounted for.
Overlap
Rule Designer checks that no branches overlap in the decision tree. For example, if one branch defines the interval [21 - 30] and another branch defines the interval [28 - 40], an error is generated since the interval [28 - 30] overlaps in that node.
You cannot check dates for gaps and overlap.