Some of the roots of the UP/RUP exist in the work of Barry Boehm and his spiral model. Its risk-driven and iterative approach influenced key UP/RUP contributors at Rational Corporation, including Philippe Kruchten, Grady Booch, Mike Devlin, Rich Reitman, and Walker Royce. Indeed, Royce collaborated with Boehm on research, writing, and projects. Boehm's well-known "anchor point" milestones [Boehm96] became the milestones that defined the boundaries between inception, elaboration, and construction. The Rational team created the UP/RUP in collaboration with customers, taking input from the "Rational Approach" they had developed through the 1980s and 1990s, and from the Objectory process they acquired from Ivar Jacobson. The core initial development was around 1995 98. The chief architect of the UP/RUP was Philippe Kruchten, an experienced architect or process leader on major applications such as the new Canadian air traffic control system, and a well-known architecture thought leader, e.g., [Kruchten95]. Although Rational had Rational Unified Process and a commercial product in mind from the start, they also wanted to communicate and promote the idea of a process more public domain and open a generalized Unified Process. This was consistent with their open Unified Modeling Language initiative. Hence, Ivar Jacobson wrote the first book to present this view, The Unified Software Development Process (1999) working from a draft of the RUP specification and product being developed by Kruchten's team. Since then, many books have been written under the appellation of simply "Unified Process" to signify similarity to the RUP and adoption of its major ideas (the best practices, the phases, the disciplines, and so forth), while not necessarily being strictly the Rational process.