I have two products A and B under the root product.When i try applying constraints between A & B ,the entire assembly is getting re aligned with the constrained part. How do i avoid this and enable 1 to 1 constraint between A & B.
This is inherent to the Instance / Reference nature of CATIA's standard assembly constraint methodology.
If you want to manipulate components of a sub-assembly independent of its containing parent, you should make the sub-assembly flexible (Right Click on the Instance > Object > Flexible/Rigid Sub-assembly). This will allow the positions of each instance in that sub-assembly to be manipulated in the context of the root assembly. Keep in mind, this will not affect the original positions in the sub-assembly (open in new window to visualize). If maintaining the new positions in the reference assembly is desired, use the 'Propagate Position to Reference' command.