You can hide or show relationship lines of all types on any diagram as follows:
Hiding all relationship lines of a particular type
1 Select View > Hide/Show relationship line(s), or right-click the diagram workspace and then click Hide/Show relationship line(s). This opens the Hide/Show relationship line(s) dialog. The dialog presents all relationship line types on the diagram, with a check box next to each type.
2 To hide a particular relationship line type on the diagram, select the checkbox next it.
3 Click OK.
Hiding or showing lines connected to selected nodes
If you select node symbols before invoking the feature then only lines connected to those symbols will be shown or hidden, as the instructions will explain. If you do not select node symbols then a comment in the instructions makes the option known to the user.