Before jumping into joints Director/Ageia requires the user to create a constraint Descriptor. A constraint descriptor is a structure that stores the required parameters that are later on used to create Linear or angular Joints.
A constraint descriptor is of the following format (syntax and parameter list) :
ConstraintDesc(cname,rbA,rbB,POCA,POCB,stiffness,Damping)
were
Cname - name for the constraint , has to [...]

Similar to Angular Joints the way in which it is created, the only difference between them is that in Linear Joint the rest length is not restricted in movement but the angular rotation of the rigid body is.

The above diagram shows that the restlength is not restricted and the angle/orientation of the rigidbody is restricted [...]