Requirements: In requirements, types of variability can exist in product line includes: a requirement
may be mandatory or optional for all or some of the end-products, a requirement might depend on
other requirements, a requirement may be incompatible with other requirements, and a requirement
may have variations in details. Each item listed in the specific context of practical difficulties, and
requirements analysis techniques used in traditional development cannot be implemented in all these
variations. There is no systematic process for identifying and managing conflicts of requirements in
the case that the requirements are written in natural language. Formal specification languages that
were provided for this purpose are very complex and difficult for non-experts