Siebel Apply and Activate

All of us know, when we do any schema level changes then we have to do Apply & Activate. This post will help you to understand what exactly happens when we do Apply and Activate. 

The Apply and Activate buttons appear in the Table and Index sections of Siebel Tools. They are a means to synchronize the logical and physical schema and also to alert other users that changes have been made to the schema.
The logical schema is stored in the S_TABLE, S_COLUMN, S_INDEX and S_INDEX_COLUMN tables in the Siebel database. The physical schema is defined in the RDBMS (IBM DB2, Microsoft SQL Server or Oracle) that is being used.
Developer does the changes in logical schema i.e. in repository. In order to those changes to be propagated to physical schema two things must happen,

1)     Siebel tools must create DDL statement corresponding to repository level change and fire that sql to the  database.This is exactly what happens when we click Apply button.

2)     Next step is to press activate button. When you click activate button, Schema version information stored in table S_APP_VER changes.

All Siebel components gets information about physical schema from diccache.dat file which resides in siebel server bin directory. This file also contains information about schema version.
Every Siebel component compares schema version information in diccache.dat file with schema information in S_APP_VER table before using schema definitions in deccache.dat file.
So in case you have any new changes and if you have Applied and Activated those changes using Siebel tools, schema version information in S_APP_VER table and dicache.dat will not match and Siebel will recreate diccache.dat file. Newly created diccache.dat file will have latest schema changes. So every time you do any change in logical schema (Repository) you have to perform Apply & Activate.