A class lets you apply a set of design rules to multiple nets; you assign a bunch of nets to a class, and then set a design rule for the class. A DDR databus is a good example where you have to match the length between all the nets in the data bus.
How do you do it - I believe you need the ARS (Advanced Rule Set) option. <Setup><Design Rules> and you'll see the Class button in the first dialog box.
Unions - look in PADS Layout help - "Unions are user-created part associations that have a strict relationship with each other, such as distance, rotation angle, top, or bottom side. A common example is placing a filter capacitor to reside on top of an IC. When a selected union is moved or placed, the physical relationship between the parts, or union members, remains unchanged."
thanks for your reply but the thing is when i select group of components after that when i did right click union options is desiabled what can i do ??? i thinks i have not licence for that ,is there any alternate option is available
Clusters and Unions do require the Clusterplacement option. It was added to all base configurations in v9.0, but was still an add-on feature in v2005.
As jduquette mentioned in a prior post, the Class option is a part of the Advanced Rule Set.