Products with new features need to be introduced on the market in a rapid pace and organizations need to speed up their development process. The ordinary way to develop products, one at a time, is not time efficient enough and is costly. Reuse has been suggested as a solution, but to achieve effective reuse within an organization a planned and proactive effort must be used. Product lines are the most promising technique and it increases productivity and software quality and decreases time-to-market. This paper describes the architecture of product line engineering process and also addresses what the design issues of product line architecture are and how a UML profile looks like for a product line by referring to the basic aspects of a case study, CelsiusTech in its Naval Product Line, SS2000.