Links that are blue and drawn with a square terminator indicate that only one instance of the data exists, and it is shared between the connected systems. In order to edit the details of that data, you must edit the cell on the upstream system connected by these links.

In the example shown in the figure below, the Geometry cell from system A is shared with the Geometry cell in system B, which is in turn shared with the Geometry cell of system C. To edit the geometry for any of these systems, you must initiate the edit operation from the Geometry cell in system A. You can either double-click the cell or right-click the cell and select Edit from the context menu.