The below link was a great help in getting some idea : https://community.emc.com/message/3567#3567
For getting a documentum format for dos extension like (doc, ppt, docx, ppptx..) using this query :
Select name from dm_format where dos_extension = 'dosExtension
This will give only the format name like crtext, msw8...
For getting the description of a documentum format, you can do a query like this
SELECT r_object_id as rid, object_name, a_content_type from dm_sysobject WHERE CABINET('/Templates') and r_object_type ='objectType
For doing a reverse mapping of documentum format to dos extension
Select dos_extension from dm_format where name = 'documentumFormatName
DFS can do a search query using this query to get the values.