Create custom index in Siebel

Create custom index in Siebel

1)From Bookshelf and from past experienc we understand custom index should be created in siebel tools first in Index object and Index column object and applied to the database and activated.(As explained in Book shelf configuring tables and columns).
2)Is the approcah of creating custom indexes for Siebel tables directly in the database(physical schema) without creating it thru siebel tools recommmended.could you also descibe the merits/demerits of this process versus approach 1

If Indexes are created directly in the RDBMS do we still have create them later in Siebel tools.If not how would the logical schema have this index.Also is that a concern that index is there in THE RDBMS and not in siebel tools