If you are coming from EBS then this post will help you to understand the difference of security model in these two application.
here is quick comparison chart all the major security features of Oracle Application (EBS) and Fusion Application side by side.
|Authorization||AOL security model
RBAC (This is optional add-on)
|FMW OPSS (this is same as RBAC)|
|Security platform||Proprietary||FMW OPSS|
|Segregation Of Duties (SOD)||No explicit functionality||Predefined SOD policies
Application Access Controls
|Technology||Prepackaged eBiz specific
configuration and management
|Management of security
|HR specific data security||Security Groups||Security Groups|