AgileAlliance published in 2001 a manifesto with the principles that all software development projects should use.
In the meantime a current is emerging that states that PMI principles and the agile Project Management are in some way incompatible.
What the author doesn’t seem to understand is that the PMBOK presents the tools and techniques that a PM can use for his/her project but ultimately is up to the PM to decide how to do the work (communicate with the team verbally or written, build iteratively or in one big bang approach).
There is also a miss conception of what is the project management process and the project life cycle. The last is the set of specific phases that constitute a project to improve management and this is dictated by the specific application area (in this case software dev). The first one must adapt to help attain the project goals.