Figure 17: A tree of frames and a few relations between the frames
Tree panes were created to show the interconnections among numerous frames. Each tree consists of nodes (that represent frames in the knowledge base) and arcs (that represent slots or relations). For example, the tree in Figure 17 shows some of the connections between Rose-Plant and other frames in the knowledge base. In this figure, Rose-Plant is the root, Rose-Plant, Hummingbird, Corolla, Petal, Calyx, Sepal, and Radial are the nodes, and parts, pollinated-by, and symmetry are the arcs.
Figure 18: The hierarchy of Rose-Plant showing where values for the (Rose-Plant parts) address are inherited from
Figure 19: The Configuration Menu for the Tree in Figure 18
To generate a tree, the user first clicks right in the white space of the tree pane. After choosing "Display Tree", the user enters the name of the root of the tree. Next, the user specifies the configuration of the tree in the next menu that appears. Figure 19 shows this menu with the configuration used to generate the tree in Figure 18. The following are some of the options on this menu:
• To the Left slots to display to the left of the root of the tree.
• To the Right slots to display to the right of the root of the tree.
• Slots Underneath slots to display below the nodes in the tree.
Figure 20: A compact tree (arc labels are attached to the frames)
Figure 21: An expanded tree (labels are attached to the arcs)
Figure 22: An expanded+ tree (arcs are shared by multiple frames)
• Tree Format specifies the format of the tree. Figure 20, Figure 21, and Figure 22 are examples of trees in these formats.
- compact puts all arc labels at the top of the tree nodes. This option is especially useful if the tree is large, since it can fit a large segment of the tree onto the screen at the same time. This keeps the user from having to depend too much on his/her Working Memory [Card:83].
- expanded puts the relation labels on the arcs, with an arc being drawn for each relation.
- expanded+ draws one arc for each relation.
Figure 23: A tree of the specializations of substance with Pretty-Print off
Figure 24: A tree of the specializations of substance with Pretty-Print on
• Pretty Print this option is used for compact and expanded trees only. Figure 23 and Figure 24 are examples of these two kinds of trees.
- NIL the nodes of the tree will only appear once. If a node is linked to multiple relations, then the relations will all be drawn to the node. This can sometimes make the tree look messy.
- T the tree can have multiple copies of the same node, such that each relation draws to its own copy of the node.
• Depth Level sets the depth of the tree.
- a number specifies how many levels the tree will be expanded to the left and the right.
- NIL indicates no restrictions will be placed on the expansion of the tree.