Purchasing Concurrent Processes

Hello Every one,

I have few questions related to purchasing concurrent.

1- Purchasing Database Administrator

     a- What is the purpose of purchasing Database administrator?

     b. Is it mandatory to run this process?

     c. How to check if this process is running on daily basis on an instance?

2- Document Approval Manager

     a. What is the purpose of this concurrent?

     b. Is this concurrent forwarded the purchasing documents for approval?

     c. Then, what is for Workflow background Engine process?

I found above concurrent while going through the Purchasing User Guide R12, but I did not find any of these two concurrent scheduled in our R12 instance.