cdef class Module:
	def __init__(self, name, provides=set(), requires=set(), common=set()):
		'''
		* Modules are identified by their name which has to be unique within the Aggregate's namespace.
		* The provides sequence contains keywords which are copied into Aggregate's _provided list.
		  Two modules providing the same export can't be linked into the same Aggregate.
		* The requires sequence contains keywords that have to be already present in the Aggregate's
		  _provided list before linking.
		* All names in the Module's namespace that don't begin with an underscore will be exported
		  into the Aggregate's namespace.
		* If you want to call one method on multiple modules, these modules must all export the method name
		  in their 'common' set. Otherwise a name collision is raised. Their methods will be called in the
		  same order in which the modules were linked.
		'''
		
		self._top = None
		self._name = name
		self._provides = set(provides)
		self._requires = set(requires)
		self._common = set(common)