In the Requirements Phase , Business Analysts usually do a Fit & Gap Analysis.
Fit is defined as a Requirement that can be achieved using Vanilla / OOTB Siebel
Gap is defined as a Requirement that cannot be achieved using Vanilla / OOTB Siebel
There are 3 Types of Gaps that Siebel Defines:-
Usage Gap is a gap that requires light to moderate configuration of standard siebel functionality
Functional Gap is a gap that needs to add a or significantly enhance standard siebel functionality
Capability Gap is a gap where there is no Siebel Solution