I guess there is not need for introduction to Audit Trail but here it is anyway. Audit trail has changed drastically from Siebel 7.X to Siebel 8.X.
In addition to the enhancements there has been one major change in the way data is stored in the Audit Trail.
In earlier versions of Siebel you could find 1-to-1 mapping of fields on UI and columns on database for Audit Trail.With Siebel 8.X Audit Trail information is stored in the encoded format to improve the overall performance for the application. So, there is no column storing Old Value and New Value. It is all dumped in encoded format in a column called AUDIT_LOG The Audit Trail business component “Audit Trail Item 2” is a VBC which decodes information and then display it in UI. Here is a screenshot showing the how the data is store in S_AUDIT_ITEM
I was able to find a nice article in Oracle Support explaining how to decode Audit Trail information. So, if you guys are interested, follow this link and you can download small PDF explaining the details.