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Navigating in the State Space
The SDL Explorer provides the possibility to interactively walk around in the behavior tree of an SDL system. This is also known as manually navigating in the state space. A dedicated graphical tool, the Navigator, is available in the Explorer to facilitate manual navigating. However, it is possible to use manual navigation without using the Navigator tool.
The Navigator is intended to be used in three different situations:
- When learning how a state space exploration tool like the Explorer works, the Navigator is a convenient tool for interactively investigating the behavior tree of an SDL system.
- When using automatic state space exploration, there is sometimes a need to start the exploration from a different starting point than the system start state of the SDL system. In this case, the Navigator can be used to walk to a suitable system state, from which the automatic exploration can be started.
- When investigating a report generated during automatic exploration, the Navigator can be used to check the alternative behaviors that are possible on the path to the reported situation.
To open the Navigator tool, use one of the following methods:
- Select Show Navigator from the Commands menu.
- In the button module Explore, click the Navigator button.
- Enter the command Show-Navigator.
The boxes shown in the Navigator represent the behavior tree transitions leading to and from the current system state. They are labelled
Up 1 (for the transition leading to the current state) and Next 1, Next 2, etc. (for the transitions leading from the current state).
To close the Navigator, click the Close quick button in the tool bar.
Moving Up in the Behavior Tree
To move one level up in the behavior tree, use one of the following methods:
- In the Navigator, double-click the Up node, or select Up 1 from the pop-up menu available on the Up node.
- In the button module Explore, click the Up button.
- Enter the command Tree-Walk 1.
To move more than one level up in the behavior tree at once:
- Enter the command Tree-Walk, followed by the number of levels to move up.
To move to the current root of the behavior tree, i.e. the top of the current path, use one of the following methods:
- In the Navigator, select Up to top from the pop-up menu available on the Up node.
- In the button module Explore, click the Top button.
- Enter the command Top.
Moving Down in the Behavior Tree
To see the possible Next nodes when the Navigator is not opened, enter the command List-Next. This gives a numbered list of all transitions leading from the current state.
To move one level down in the behavior tree, use one of the following methods:
- In the Navigator, double-click one of the Next nodes, or select Goto from the pop-up menu available on the Next nodes. This will follow the branch one step.
- Enter the command Next, followed by the number of the Next node, i.e. the number of the transition to execute.
To move more than one level down in the behavior tree at once:
- Enter the command Random-Down, followed by the number of levels to move down. For each level, a transition is chosen at random.
- Enter the command Continue-Until-Branch, or in the Navigator, select Continue from the popup menu available on the Next nodes. This will follow the branch several steps until there are more than one transition possible
Moving Along the Current Path
The current path can be seen as the path in the behavior tree that has been explored last. It is set up when going to a report (see Going to a Report) and when interactively walking down the behavior tree.
The transitions making up the current path are labelled with three asterisks "***" in the nodes in the Navigator. However, no such marking is present when the transitions are listed with the List-Next command.
To move up along the current path, use the Up or Top commands as described in Moving Up in the Behavior Tree (above).
To move one level down along the current path, use one of the following methods:
- In the Navigator, double-click the Next node labelled with three asterisks "***", or select Goto from the pop-up menu available on this node.
- In the button module Explore, click the Down button.
- Enter the command Down 1.
To move more than one level down along the current path at once, enter the command Down, followed by the number of levels to move down.
To move to the bottom of the current path, use one of the following methods:
- In the button module Explore, click the Bottom button.
- Enter the command Bottom.
Redefining the Current Root
The current root of the behavior tree is initially set up to the system start state. The current root is automatically redefined to the current state when using MSC verification (see Verifying an MSC). It can also be redefined as an effect of changing explorer options (see Affecting the State Space).
In addition, you can at any time redefine the current root to either the current state or back to the system start state. To do this, enter the command Define-Root. Select or enter Current to redefine the current root to the current state. Select or enter Original to redefine the current root to the system start state.
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