"Layers"

[Scott.Fahlman@B.GP.CS.CMU.EDU]

I think it would help us all to follow these discussions if, when people
want to talk about "N-layer networks" for some N, they would make it clear
exactly what they are talking about.  Does N refer to layers of units or
layers of tunable weights?  If layers of units, are we counting only layers
of hidden units, or are we including the output layers, or both the input
and output layers?  I think I've seen at least one paper that uses each of
these definitions.  Unfortunately, there seems to be no universal agreement
on this bit of terminology, and without such agreement it requires a lot of
work to figure out from context what is being claimed.

Sometimes a researcher will carefully define what he means by "layer" in
one message -- I think Alexis Wieland did this -- but then launch into a
multi-message discussion spread over a couple of weeks.  Again, this makes
extra work for people trying to understand the discussion, since it's hard
to keep track of who is using what kinds of layers, and it's a pain to go
back searching through old messages.

Perhaps I'm the only one who is confused by this.  Does anyone believe that
there *is* a standard or obvious definition for "layer" that we all should
adhere to?  It would be nice if we could all adopt the same terminology,
but it may be too late in this case.

-- Scott