Section 1: Managing Files and Basic Tasks

• Loading a Graph from File
• Starting the Graph Layout Algorithm
• Saving the Status of a Graph
• Printing a Graph Visualization

Now we will load a graph for visualization. Graphs are stored in files with a .daVinci suffix, containing a so called term representation. This format only defines the structure of a graph, but has no layout informations such as the coordinate of a particular node. The term representation format is discussed in detail in the reference chapter. To load a graph, you need the file browser for selecting a file name. You can get a browser by selecting menu File/Open... (i.e. move the mouse pointer to the File pull down menu and press the right mouse button which will show the File menu. Then move the mouse pointer to the Open... menu entry by still pressing the right mouse button and finally release the mouse button when you are over the Open... menu entry). This will pop up the file browser for opening a graph.

The file browser has two different lists: One for the directories inside the current directory and one for the files in the current directory. The current directory is always displayed in the Selection field of the file browser. Now you can browse through the directories of the file system of your computer by double-clicking the list elements of the Directories view with the left mouse button (the left mouse button is used to select or manipulate objects visible on the screen, whereby the right button is used to choose from a menu). A double-click on '..', the first element of the directory list, will move to the parent directory. When there is not enough place to show all directories or files, then you can use the vertical scrollbars at the right side of the lists to move the focus. Finally, go into the example_graphs/ directory of the daVinci distribution. Ask your administrator if you are not sure about the location of the daVinci distribution on your file system.

When you are inside the example_graphs/ directory, click on the Types option button to select the Graph Files filter. This will remove all files without suffix .daVinci from the files view. Now double-click on file graph_example.daVinci to load this graph in daVinci. This finishing action will automatically close the file browser.

Starting the Graph Layout Algorithm

As you can see on the screen, all graph nodes are automatically placed on horizontal levels such that all (directed) edges between two nodes are pointing downwards. This is called a hierarchical visualization of a directed graph. Other styles of graph layout are currently not supported by daVinci. Background information about graphs can be found in the concept document.

Except of assigning nodes to levels, the graph layout algorithm is not used directly after loading a graph, to display it as soon as possible. By looking at the graph visualization, you can see that the layout is not as good as it can be. For example, several edges cross eachother, which makes the layout confusing and somehow unattractive. You can see the total number of edge crossings of the current graph layout by opening a statistic window with menu View/Graph Info.... Improving the graph layout can be done by reordering the nodes at each level such that the number of edges is reduced. daVinci offers an automatic graph layout algorithm for this task. Start this algorithm by using menu Layout/Improve All. After doing so, you will notice a significantly improved layout. You can read more about graph layout in the concept document.

In daVinci, a graph is drawn top-down by default, so edges are usually pointing downwards. You can choose one of the other three layout orientations (upwards, to the left or to the right) with menu Layout/Orientation. For example, try to rotate the layout by selecting menu Layout/Orientation/Left to Right.

Saving the Status of a Graph

Again, you need a file browser to save the current layout to a status file. One way to do so is by selecting menu File/Save As.... But at this time, we will use the icon bar of the base window for more comfort. Move the mouse pointer to the save button which looks like this:

Button of the icon bar to save a graph

In the file browser, you have to choose the file type you want to save by using the Types option button: Either Status Files (default) or Graph Files. Saving the current graph in term representation format by using type Graph Files does not make sense at the moment, because the structure of the graph is still the same, which means that you would get the same file as loaded before. So use the default type Status Files such that the title of the browser window shows "Save As Status".

The browser usually suggests a name for the file you want to save. The filename of the graph (term representation) you have loaded before is graph_example.daVinci, so the suggested filename is graph_example.status. Status files should usually have suffix .status. Unfortunately, the suggested filename already exists (as you can see in the Files view of the browser) and you do not want to overwrite it. By the way, the browser will ask the user before overwriting files. So choose a new name for your file by editing the Selection field of the browser. Click in the field to get a text cursor and erase the filename (but not the directory) with the Backspace key. Then enter a new filename, e.g. my_graph.status, and press the Save push button to start the saving operation.

If you do not have write permissions for the example_graphs directory of the daVinci distribution, then saving will fail and a notice window will appear. In this case, open the browser again to repeat this operation, but at this time choose another directory where you have permissions to write, for example your home directory.

Printing a Graph Visualization

But at this time, we will use the keyboard instead of the mouse for choosing this menu operation. Press the keys Alt and f simultaneously which is usually written as Alt+F. This will open the File menu. f is the underlined character (mnemonic) of the File menu, the keyboard equivalent for mouseless operation. After opening the menu with these two keys, you can navigate through all menus with the four cursor keys of the keyboard. By pressing Return, you select the currently highlighted menu entry. In an opened menu, you have another option to choose from a menu by pressing the mnemonic character (at this time without the Alt key!) of one of the menu entries. For example, when the File menu is open, you select Print... by pressing the p key. So the overall keyboard command to select this particular menu is Alt+F P (upper case letters are not significant here). You can read more about keyboard usage by following this reference.

After opening the print dialog window with one of the methods described above, you have the opportunity to set some options before the file will actually be printed. Lets asume you want to print the currently loaded graph on one of the PostScript printers in your network. First of all, you need to know the UNIX command used for printing PostScript files at your site. For example, if you usually use command