Diego's version:

diego_datamapper.rb

class User
	include DataMapper::Resource
	has n, :projects
end

class Project
	include DataMapper::Resource
	
	belongs_to :user, :key => true
	has n, :steps
end

class Step
	include DataMapper::Resource

	belongs_to :project, :key => true
	has n, :images
end

class Image
	include DataMapper::Resource
	
	belongs_to :step, :key => true
	has n, :notes
end

class Note
	include DataMapper::Resource
	
	belongs_to :image, :key => true
	has n, :comments
end

class Comment
	include DataMapper::Resource
	
	belongs_to :note, :key => true
end