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 be unique
rbA - Rigid body A ( created via createrigidbody() )
rbB - Rigid body B ( created via createrigidbody() )
pocA - point at which the joint is created within rigid body A’s coordinate
pocB - point at which the joint is created within rigid body B’s coordinate
float Stiffness - Value of the stiffness of the constraint
float damping - Value of the damping of the constraint.