These are the shortcut keys when working within the diagram:

• Pressing F5 will reload the diagram.
• Pressing Ctrl+F4 will close the diagram.
• Pressing Ctrl+T in the diagram will select the node in the tree that corresponds to the diagram.
• Pressing Ctrl+W when in the diagram will bring up the Walker diagram.
• Pressing Ctrl+F will bring up the search function in the diagram.
• Pressing the Ctrl key and then using the mouse wheel will enable you to zoom in and out from the mouse cursor.
• Pressing the Alt key and then clicking with the left mouse and dragging will enable panning, as with the toggle hand in the diagram toolbar.
• Pressing F2 when a column is selected will allow you to rename the column.
• Pressing F2 when a table is selected will allow you to rename the table.
• Pressing Ctrl+A will select all objects in the diagram.
• Pressing Ctrl+X will cut the current selection.
• Pressing Ctrl+C will copy the current selection.
• Pressing Ctrl+V will paste the current clipboard contents.
• Pressing Delete will delete the selected item.
• Pressing Ctrl+S will show the Save diagram as dialog (refer to Saving Diagrams for details).
• Pressing Ctrl+P will show the Print dialog
• Pressing Ctrl+Shift+Left mouse will draw on the diagram.
• Pressing Ctrl+Shift+C clears drawing from the diagram.
• When a relationship is selected pressing Ctrl + [ brings the FK table into view. 
• When a relationship is selected pressing Ctrl + ] brings the PK table into view. 

Also see Repository Tree Shortcut Keys for details.