Action type indicates an action routine described by a dive number. Sub-action type is a component of action type, where each combination of the presented sub-action types can produce an action type, where different action types can share the same sub-action type. In Figure 2, the green branch denotes different kinds of take-offs; the purple, yellow, and red branches represent the somersaults with three positions (i.e., straight, pike, and tuck) in the air, respectively, where each branch contains different somersault turns; the orange branch indicates different twist turns in the air, combined with somersaults; the light blue denotes entering the water. In Figure 3, the action-level labels describe temporal boundaries of valid action routines, while the step-level labels provide the starting frames of consecutive steps in the procedure.