Documentation of the model is published on SpineModel.info, providing a explanation and information on how it can be applied. There is also a wiki-style catalog of items at the five different spine levels.
The Spine Model is an extension of Kent Beck’s framing of eXtreme Programming ideas as Values, then Principles, then Practices. We added the way Needs where modeled in Marshall Rosenberg’s Non-Violent Communication above Values. Then we added Tools on the bottom because that made sense. That formed the basis of the Spine Model structure, but the thinking and the way we apply it has been influenced by many people over time and it continues to evolve today.