Outline view
The outline view gives you a quick way to enter lots of data, and an alternate way to look at outline-like diagrams. To open the utility drawer, click its toolbar icon or select it from the View menu. Then click the Outline tab at the top of the drawer to switch to the outline view.
The outline view shows any shapes you've created on the canvas, arranged hierarchically according to the lines that connect them. Likewise, as you enter text into the outline, shapes are automatically created and connected on the canvas with corresponding text.
To start working with the outline view, just click an existing item, or double-click in an empty area to create a new item. While you work in the outline view, the following keys can be used to create and arrange items:
Press Return to create a "peer" of the currently selected item. Peers appear on the same indentation level in the outline, and, if they are beyond the top level, have connections from the same parent object in the diagram.
Press Tab to indent the currently selected item, making it a "child" of the item above it in the outline. A connection line is drawn in the diagram from the parent object to the child object.
Press Shift-Tab to outdent the currently selected item, making it a peer of what used to be its parent.
Press Escape to switch between selecting an item and editing the item's text.
There are also keyboard shortcuts especially for quickly building outlines. Check the Keyboard Shortcuts file in the Help menu for details.
An item can be dragged around the outline view by its handle, the dot or triangle to the left of each item. Dragging an item with children brings its children with it. While you drag an item, a black line appears to show the location and indentation level the item will have when you drop it.
A group of objects on the canvas is shown as a single item in the outline, surrounded by brackets. Click the right-side bracket with the arrows to see the objects inside and edit their text.
Click the plus button at the bottom of the outline view to add an item. Select an item and click the minus button to remove it. The gear menu replicates the Outlining submenu of the Arrange menu.
There are two checkboxes for controlling how the diagram behaves in reaction to your editing the outline. Select Auto lay out diagram to have OmniGraffle arrange the shapes in the diagram every time you create or move an item in the outline view. The arrangement is based on the current settings in the Automatic Layout inspector. Select Auto restyle objects to conform to the outline style selected in the pop-up menu above.
The pop-up menu, at the very bottom of the drawer, contains the available diagram styles. While you edit the outline, objects in the diagram are created to match the objects in the diagram style. A preview of the selected diagram style appears above the pop-up menu. If you change the diagram style, objects already on the canvas change to match the new style, unless they have been styled manually. You can force manually styled objects to conform to the diagram style by selecting them and using the command Edit ‣ Outlining ‣ Apply Diagram Style.
While the outline view is handy for entering lots of information quickly, an outline can't always perfectly represent the relationships in a complicated diagram. Objects with more than one parent, lines connected to other lines, and ancestry that reverses its direction ("I'm my own grandpa!") are all examples of the kinds of things a simple outline can't properly show. In these cases, the outline view tries its best to be accurate. If your diagram is not strictly tree-like, you should probably not rely on the outline view very much.