Is it possible to add additional labels to an arrow, like the relational arrows have multiple text fields?
Not currently, but you're welcome to add it as a feature request.
I haven't found a way to add a label to an existing arrow, but I did find a way to create labeled arrows using one of the built-in UML shapes.
- First, locate the set of UML shapes at the left panel. It is listed by default (if you cannot find it, click on "More shapes..." and make sure that "UML" is enabled). Among the 24 UML shapes, there are several kinds of arrow/label combinations. For example, if you want to get a line with a label, choose "Generalization" shape.
- Drag the generalization arrow to your painting. The result will be a line with two endpoints and a text label with an orange dot. This orange dot is the anchor of the label, if you move the arrow, the anchor and the text will move along.
- If you want to style the arrow differently, just click on the arrowhead icon in the toolbar and select a different arrowhead. E.g. if you want to remove the arrowhead, pick the top option ("None").
- The label text can be changed by clicking on the label. It can even be moved by moving the orange dot around. The label will still be positioned relative to the arrow.
- The appearance of the line can be customized as well. The format menu allows you to change the line width, line style (dashed / dotted / solid / ... ), color and many other properties.