Identifying

representing and implementing the variability in domain engineering have a direct and important effect on application engineering;they are the emphases of domain engineering.Especially

building the reasonable and flexible DSSA (Domain Specific Software Architecture) in domain design

separating fixed parts and variable parts of systems

assigning the system elements between the DSSA and components reasonably

and implementing the variability as components are the nucleus and key work of domain engineering.This paper discusses the corresponding solutions to the variability of object-oriented domain design

employing the research results of design pattern and object-oriented framework;and presents how to use these solutions to deal with the variability in the domain design of POS (Point-of-Sale) domain.