Diagram Styles
Diagram styles are OmniGraffle documents that define an appearance you can apply to an outline or a diagram. There are infinite ways to represent the same data; a diagram style helps you indicate just how you want the data to be represented.
The main situations when diagram styles come in handy are when you write an outline with OmniGraffle's outline view (use the Diagram Style pop-up menu below the outline) or when you import an OmniOutliner file (use the importing dialog that appears). In these situations, the diagram style translates text items into visible objects. Several diagram styles come with OmniGraffle; try using the outline view with various diagram styles to see their effects.
To create a diagram style, just create a simple, one-canvas, one-layer OmniGraffle document containing some interconnected objects styled the way you want. A diagram style should be a strictly tree-like structure; this means the connection lines should create a hierarchy without doubling back on themselves. If you intend to import OmniOutliner files with multiple columns, you can use a group of shapes, rather than a single shape, to represent each item. In this case, you should put a text label on each object so that you can associate columns with them when opening the OmniOutliner file.
When you apply a diagram style, the items of the outline are put into a diagram that matches the diagram style's shapes, connection lines, and automatic layout settings. Items at each level of the outline become shape objects matching objects at the same level of the diagram. If the outline has more levels than the outline style, the deeper items use the styles of the deepest level of the outline style.