Populate fields based on Assignment Group in Incident

Hi all,

I have two scenarios on the incident form.

1. I need to set category field mandatory based on specific Assignment Groups
2. For those specific Assignment Groups and Configuration items are not (ABC,XYZ) then description field should be mandatory.

First I created system properties to fetch the sys_id of Assignment Groups and ci. and have used display business rule to fetch system properties values and i have used scratchpad value in on Change Client Script ,but it is not working properly anyone can help me on this, thanks