Configuring Siebel eBusiness Applications > Configuring Tables and Columns >

About Extension Columns

An extension column is used to store custom attributes. There are three kinds of extension columns:

• Static extension columns. Extension columns are included in static extension tables for customer use. They are named ATTRIB_nn, where nn is a value between 01 and 47 (for example, ATTRIB_13). Modifying or deleting static extension columns is not recommended.
• Custom extension columns in an extension table. These are columns added by the developer to an extension table. They have the prefix X_ in their names.
• Custom extension columns in a base table. These are columns added by the developer to a base table. The relational database system that you use with Siebel applications determines whether or not this is allowed. When the database system supports custom extension columns in base tables, it may be preferable for performance reasons to add them there, rather than to an extension table. Performance may be affected if the extension columns are added to an extension table, because extra SQL is generated to join to the extension table.