The Link tools 
are used to trace links between objects.
A link is made up of two points or more: a starting point, a final point and possibly intermediate points. When a link is selected, the selection marks appear on each point of the link.
When you click on one of these selection marks you can change the position of the intermediate corresponding point by moving the mouse with the left button pressed, then releasing the button at the desired position.
But there is a restriction for the extreme points of the link: the new position of the point must always be inside the attached link, or else this position will be invalidated.When you click on a link (outside the selection marks) and you move the mouse with left button pressed, the link breaks and an intermediate point is created at the same place where the button is released.
The link is created when each end has been defined. The starting point corresponds to the first valid click, i.e. the first click performed on an object; all the previous invalid clicks are ignored. The final point is defined by clicking another object, compatible with the starting object.
All the rejected clicks are considered as intermediate points of the link. They correspond to clicks outside of objects or clicks on invalid objects. When each end has been validated, the link is then traced between the two objects linked, either by means of a single line, or by means of a broken line connecting all the intermediate points.
The link currently created can be cancelled by pressing the Esc key or by clicking with the right button of the mouse (which invalidates the link creation mode).
The graphical links correspond to 4GL instructions:
Single link
Toward a transaction: corresponds to 4GL instruction PROCESS.
Toward the end of the program: corresponds to 4GL instruction TERMINATE.
Double link
Between two transactions: corresponds to 4GL instruction EXECUTE.
Between a transaction and an interactive program: corresponds to 4GL instruction CALL.
Between a transaction and a batch program: corresponds to 4GL instruction CALL.
Loop link
Looped on a transaction: corresponds to 4GL instruction PROCESS (this link is used to recall the same transaction after updating the fields).
Click below for further information about:
the CALL 4GL instruction.
the EXECUTE 4GL instruction.
the TERMINATE 4GL instruction.
the PROCESS 4GL instruction.