This fall I took a Product Design and Development class at Babson. Our textbook for the course was Designing for Growth by Jeanne Liedtka and Tom Ogilvie. The book is a design thinking primer for MBAs and guided our semester-long design project. The design process asks four questions: "What is? What if? What wows? What works?"
You can read a preview of the first few chapters here. The graph below comes from chapter two.