SRFDiff has been introduced in Siebel 8.1 and "Using Siebel Tools Version 8.1" > Chapter 12: Managing Repositories > Comparing Two Repository Files Using SRFDiff explains how to use it. There it mentions about "major schema version" and "minor schema version".
"major schema version" comes from S_APP_VER.DB_SCHEMA_VER column and "minor schema version" comes from S_APP_VER.DB_MINOR_VER column. They are inserted while Siebel Database is set up