Software product line has emerged as an attractive phenomenon within organizations dealing with software development process. It involves assembly of products from existing core assets, commonly known as components, and continuous growth in the core assets as production proceeds. Organizations trying to incorporate the concept of software product line to reduce development time and cost require certain rules to be followed for successful development and management, they also require a direct procedure to evaluate the current maturity level of the process. In this work certain rules for developing and managing a software product line are put forward. Additionally, a fuzzy logic based software product line process assessment tool (SPLPAT) has been designed and implemented on the basis of developed rules for software product line process assessment. SPLPAT can be used to assess the process maturity level of software product line, and it provides an opportunity to handle imprecision and uncertainty present in software process variables. Four case studies were conducted to validate the framework, and results show that SPLPAT provides a direct mechanism to evaluate current software product line process maturity level within an organization. The results of the developed software product line process assessment approach were compared with the existing CMM-level of the organization in order to evaluate the reliability of the presented approach and to find out how effectively an organization can execute software product line process when it has already achieved a certain CMM level.