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October 1997

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Subject:
From:
Peter Willaert <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Wed, 8 Oct 1997 15:59:19 +0200
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Hello Ray,

Part numbering starts very easy for most companies. However,
over time it gets politically *very* loaded, especially if you
try to change it afterwards. So it's very wise of you to think
before you act.

We have been changing our PNS (part numbering system) recently,
and so learnt quite a few things, some of them I'm glad
to share with you. There's also some literature you could
try to get, especially in the domain of PDM (Product Data
Management).

Historically part numbers are used for 2 functions :

 1. identification
 2. classification.

The first one being obvious, the second  one because people want
to know something about the part or drawing they are referring
to.

To do the identification, a simple strategy like "next available number'
works great. However, because of the second req'mt, most people have a PNS that
somehow divides the available number space in segments, and assign
new part numbers in the  segment they 'belong'.  E.g. :

        1.xxxxxx.r are drawings
        7.xxxxxx.r are catalog parts
                7.100xxx.r are resistors
                7.200xxx.r are capacitors
        8.xxxxxx.r are manufactured parts (BOM's)

On top of that, people sometimes require that drawing numbers
and BOM's of the same part were identical (leading to the
familiar discussion of rev'ing a BOM because of a typo in the
drawing).

This approach can be dated back to times where there were
no computers to help people with their jobs.  However,
today, it is no longer a viable approach, because of the following
reasons :

1. computers have no problems with simple numbers. In fact,
they prefer them, because otherwise they have to do syntax checks
(is it a viable part number, etc).

2. computers are very good in managing relations between
objects.  So a computer will perfectly know (and never forget)
that drawing A belongs to part B, and vice-versa.

3. the big risk with putting classification into the PNS
is that over a longer time, your perception
of classification is prone to change.  Only very
simple classifications do not change over time, like drawing formats
(unless of course you go from ANSI to ISO), or the difference
between drawings and BOM's.  But as soon as you go deeper
in classification, your system gets very susceptible to
classification problems. E.g. think about the rise of SMT, which
has forced a lot of companies to code the same part twice.
Or a digital potmeter, is it a resistor or an EPROM ?
So the problem is : if you have to change your PNS because
of classification problems, you violate rule one, which says that
you never, never should change the ID of a single part or
drawing, or it will come back and haunt you for ever.

So my advice to you would be :

1. choose a ultra-simple numbering scheme e.g. 1 character to
discern between drawings (documents) and parts, followed by
as much digits as you can foresee (probably six will do), followed
by 1 or 2 revision characters.  This will identify uniquely
and safely every part, document, BOM, tool.

2. do not make a hard connection between part numbers and document numbers :
let the computer put the part number on the document automatically,
if you need to plot the document.

3. device a classification scheme that serves you right now (don't make
it too difficult), and for every classification code, make up a kind of
generic description that will fit most of the objects in the class.
(all MRP/PDM systems typically use a part number and a short description
of 20 to 60 characters). Manage these descriptions, and make sure that
all things that you want to classify together, have a similar description,
e.g.

RESISTOR, 0805, 100 OHM, 1%


In this way, if you do any kind of search for a part, you are sure that
all resistors will turn up (and you don't loose the misspelled ones).
Should the need arise, you then can always change the classification
scheme without touching the part numbers, and you can even automatically
modify the descriptions of existing parts to distinguish them from
newer parts.  In the example, you could e.g. add the dissipation.

This is in a nutshell what I have to say. Good luck !

Peter Willaert
Agfa-Gevaert

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