Chains are manipulated using inverse kinematics (IK) and forward kinematics (FK). The method used depends on what part of the chain you manipulate.
IK is a goal-oriented way of animating: you move the effector (end) of a chain in place and Softimage calculates the angles at which the previous joints in the chain must rotate in order for the bone or end of the chain to reach its goal. This process is called solving.
IK is an intuitive way of animating because it's how you traditionally think of movement. For example, when you want to grab an apple, you think about moving your hand to the apple (goal-oriented).
It's also a quick way of creating poses which you can then animate, keying either the effector's translation or the bones' rotation values. For more information, see Animating with Inverse Kinematics.
FK allows for complete control of the chain's behavior because you rotate each joint's position. Only the angle of the selected joint is affected; all other joint angles are preserved. Positioning a skeleton's hand to grab an apple means rotating each joint in the arm, from the shoulder to the wrist and fingers.
However, using FK allows you to create many types of movements that may not be possible to animate with IK alone. For more information, see Animating with Forward Kinematics.
Kinematics and Transformations
Before you start animating your character, it is important to understand how animating transformations work in Softimage. There are several issues related to local and global animation, as well as animating transformations in hierarchies (such as skeletons). For information on these topics and more, see Animating Transformations [Animation].
You cannot key the global position or orientation of bones; however, if you wish to animate a bone globally, you can prevent the bone from inheriting its parent's position or rotation. To do this, open the bone's Local Transform property page and deselect the appropriate Constrain option (Position or Orientation). See Animating Transformations in Hierarchies [Animation] for more information.
