The process of displaying the ancestors or descendants of a given node in the XGinseng display is called ``describing the node''. Nodes may be described in four different ways, each corresponding to one of the description buttons -- , , , and . Describing a node's descendants means displaying those nodes dominated by the selected node and drawing all the arcs between them. Similarly, describing a node's ancestors means displaying those nodes that dominate the selected node and drawing the arcs.
The two operations display those nodes that directly dominate (or are dominated by) the selected node. That is, these nodes are at one end of an arc that has the selected node at the other end. For completeness, ancestor nodes are fully described: All of the first generation descendants of an ancestor node are displayed, which ususally means that nodes that do not directly dominate the selected node are also displayed. Suppose that, in Figure 6.3 you selected on node m9. Then the ancestor node m10! is created and displayed, but the node 0 is also displayed for much of the meaning of m10! depends on node 0 being visible.
The two operations recursively call the selected display operation on the nodes they've built. Thus, continues downward in the network displaying the descendants of the selected node's descendants, then their descendants, and so on until base nodes (nodes with no descendants) are displayed. Likewise, continues upward in the network describing the ancestors of the ancestor nodes, then their ancestors, until undominated nodes are displayed.
Figure 6.3: Node m9 after having its 1st generation ancestors and descendants
displayed.
Executing a Describe Command. The four describe commands are invoked in exactly the same way: First you pick the function you want to perform, then you pick the node on which you want to perform it. Thus, first click with the left mouse button on one of the four describe commands - , , , or . The selected button will be displayed in reverse video to highlight your selection. Then click with the middle mouse button over the node you want to describe. Wait for the nodes to appear in the Display window -- if a large number of nodes need to built this process may take some time. When the selected button returns to its normal coloring the process is complete. If the selected node cannot be described in the chosen manner, then a message will be displayed in the Dialogue Box. For example, in Figure 6.3 node m10! happens to be undominated in the current SNePS network. If either or is called on m10!, the message will indicate that m10! has no ancestors.
Aborting a Describe operation. If you click on a describe button (causing it to be displayed in reverse video) and then decide not to describe any node in this fashion, you can abort the operation by clicking with the right mouse button over any node in the Display window. The button will return to its normal coloring and you may continue with no change in the display.