Use the various link buttons on the Diagram view toolbar to create links between elements. After you select a link from the Diagram view toolbar, the cursor changes to the pointer that follows if the location is valid for the start or destination of the link.
To draw a relationship link between elements:
On the Diagram toolbar, click the appropriate link button for the link you want to draw on the diagram. The button remains depressed.
In the Diagram view, click the source element.
Drag the link to the destination element. (If your destination element is outside the visible area, the Diagram view scrolls as you drag.)
Drop when the second element is highlighted.