Overview -> Tutorial -> About Scaling, Abstractions, and Navigation

Section 3: About Scaling, Abstractions, and Navigation

This tutorial section covers the following exercises:

Get an Overview with Scaling

First you need to load a graph in daVinci by using menu File/Open.... We suggest to use file graph_example.daVinci in the examples directory of the daVinci distribution again (refer to section 1). Afterwards, start the graph layout algorithm with menu Layout/Improve All.

Scaling is a feature to reduce the size of a probably large graph visualization for getting an overview. In a scaled graph, some details are dropped (e.g. the text of nodes is not drawn), but all the other interactions are still available. So for example, you can even use fine tuning in a scaled drawing of a graph. One way to reduce the scale is by selecting menu View/Fit Scale to Window. Do this right now! A new (maximal) scale is calculated and set such that the graph is completely visible in the base window. Of course, this modifies the scale only if the graph is larger than the base window.

Now open the scale dialog by using menu View/Scale.... In this window you can set the scale to any rate between 1% and 100%. Simply move the slider to some arbitrary values and observe the effect on the visualization. Pressing button Fit to Window in the dialog is the same as selecting the menu you have just used before. You cannot magnify the graph this way (i.e. there is no scale >100%), but you can use a larger font for magnification as it is discussed in the previous tutorial section. Before going to the next exercise, set the scale back to 100% (there are different ways to do so, for example by clicking on the Large label in the scale dialog) and afterwards finish the dialog by pressing the Close push button.

Using Abstractions to simplify a Layout

Interactive abstractions are used to hide particular parts of a graph that may be uninteresting or confusing. Abstractions are temporary operations that can be undone at any time. Select some node in the graph that has at least one child node. Now you can fade out the subgraph of this node by selecting menu Abstraction/Hide Subgraph. After doing so, the children of the node are removed from the visualization and the selected node is drawn with an icon showing a pair of scissors to emphasize the applied abstraction:
Node with a hidden subgraph You can restore the subgraph of the selected node by using menu Abstraction/Show Subgraph. Make sure to select a node with a hidden subgraph, otherwise the show operation is not available. Try to hide three or four large subgraphs. You can see that the position of the other nodes is not affected by this operation, to reserve the place until the subgraph is shown again. So maybe a lot of unused space is present in the visualization after hiding some subgraphs. Take advance of this space by selecting menu Layout/Improve Spacing which will result in a more compact layout. Now you can restore the original layout by using menu Abstraction/Restore all Subgraphs to restore all subgraphs. Because the place of the subgraphs is occupied after compactification, the layout may not look as it looked before the abstractions, but with the new incremental layout introduced in daVinci V2.1 you'll get a quite good layout compared to the messy one you got in former versions.

Another abstraction is hiding all the edges of a selected node: Both the incoming (from the parent nodes) and the outgoing edges (to the child nodes). The three operations for edge abstractions are also available in the Abstraction menu. After hiding the edges of a selected node, they are removed from the graph visualization and the node is drawn with a rectangular border to emphasize the applied abstraction:

Node with hidden edges

Navigation Features to browse in a Graph

For the last exercise we will come to the operations of the Navigation menu. First, select an arbitrary node in the graph. To see the parent-, sibling- or child nodes of the current selection (the siblings are the children of all parents of a particular node), choose one of the first three menu entries of the Navigation menu, e.g. Navigation/Select Children. This will clear the current selection and the corresponding set of parent, sibling or child nodes is selected, depending on the choosen operation. You can even select more than one node before using these operations to find all of their parents, siblings or children (the Using the Mouse document explains how to select more than one node at a time).

A very useful feature is the navigator dialog which appears after using menu Navigation/Navigator.... Select exactly one node in the graph and press one of the four arrow buttons of the navigator dialog to go to the next node in the corresponding direction. This way you can easily browse a graph by hopping from node to node. The speed of animation, used for scrolling to the new focus point, can be adjusted with menu Options/General Settings.... You can also use the cursor keys of the keyboard to trigger navigation, so usually you do not need the navigator dialog. Check button Structural Navigation is explained on the navigator dialog help page of the user interface documentation.

Finally we will search for nodes with a specified text by using the find dialog. Select menu Navigation/Find... to pop up this window. Now enter the substring you are looking for in the Find field. If you have loaded file graph_example.daVinci, then for example type a 6 and press the Find push button afterwards. This will search for a node with a text containing the 6. Press Find again to go to the next match.

After playing a little bit with these features, close both the find- and navigator dialog by selecting the Close button, if not already done.

End of section 3
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daVinci V2.1 Online Documentation - Page update: June 15, 1998