organization levels

[Alain Grumbach]

A couple of weeks ago, I sent this mail :
%   Being working on hybrid symbolic - connectionist systems,
%   I am wondering about the notion of "organization level",
%   which is underlying hybrid models.
 
%   A lot of people use this phrase, from neuroscience, to cognitive
%   psychology, via computer science, Artificial Intelligence :
%   (Anderson, Newell, Simon, Hofstadter,Marr, Changeux, etc).
 
%   But has anybody heard about a formal description of it ?
%   (formal but understandable !)
 

Thank you very much ...
	Hendler, Olson, Manester-Ramer, Schrein, Cutrell, Bovet,
	Tgelder, Sejnowski, Sanger, Sloman, Rohwer
... for your answers. I shall try here a summary of these answers
and put forward a framework of a formal point of view.

1. Answers :
1.1  Points of view :
A lot of phrases are used to qualify level hierarchy, denoting 
quite different points of view :
	organization levels
	description levels
	abstraction levels
	analysis levels
	integration levels
	activity levels
	explanation levels
To name each level, a lot of words are used, which, of course, should
be associated with some of hierarchy phrases :
	computational, algorithmic, implementational
	sensors, synapses, neurons, areas
	task, implementation, virtual machine
Several hierarchy structures are mentioned :
	linear
	tree
	oriented graph without circuits
	oriented graph with circuits (from processing point of view only)
	
1.2. References :
Many references are given : Steels, Fodor, Fox, Honavar & Uhr,
Jacob, Churchland & Sejnowski, Bennett & Hoffman & Prakash
the last one : Bennett & Hoffman & Prakash, being a formal theory dealing
with levels. Unfortunately I have not read it yet, as it concerns the ninth
chapter of a book; R. Rohwer will write a more direct condensed version
of it.

2. Sketch of an organization level description :
2.1 Intuitive issues :
2.1.1 Who ?

First it must be emphasized (or remembered) that an organization level
hierarchy consists in a point of view of an OBSERVER about an OBJECT,
a PHENOMENON, etc. It is not an intrinsic caracteristic of the object,
the phenomenon, but a property of the situation including the observer
(his culture) and the observed entity (from an epistemologic point of view).

2.1.2 What ?
I say above that the organization level concerns an object, a phenomenon.
Let us give some examples:
	a book, a house
	an image, a sentence, this mail
	a processing unit : computer, engine, tv, living being, etc
	a set of  objects, processing units (society, ant colony)
	etc
Some of them live in interaction with an environment (processing units),
others are static, closed entities (book, house).

2.1.3 "Level" , "Organization", "Hierarchy" :