Siebel uses Denormalized Columns to improve the performance of query operation in view where data visibility is restricted using Siebel View modes like Organization, Position etc. Denormalized columns are generally created for columns most frequently used for query like Contact First Name, Last Name etc. These denormalized columns are created in Intersection tables of the base table with Position, Organization tables. This provides an added improvement while querying for commonly used fields in My Contacts or All Contacts (Organization Visibility) views.
For example in My Contact View, there would be a by default where clause on S_POSTN_CON table on Position Id. When user queries in the view for a particular first Name or Last Name, without the denormalized columns, SQL generated would have where clause on S_CONTACT as well as S_POST_CON table
By having the denormalized column, the SQL generated would have where clause only on Single table and performance of the query will be faster. For denormalized column, Siebel ensure that if you are updating the data using any standard Siebel method (UI, EIM, EAI) the value in denormalized columns are automatically kept in synchronization. But if you are updating any such columns using direct SQL (not supported by Siebel), these denormalized column do not get updated.