Despite my "a picture paints a thousand words", I'm still having trouble understanding your data.

For example, in the following two lines, only the presence of a part no for the last manufacturer distinguishes them. Doesn't that make the second a duplicate of the first with missing information? Ie. redundant? 

NGK_STK.  NGK_P/N  NGK ALT  ACCEL  AC_DELCO  AUTOLITE  BECK/ARNLEY
1027      AP9FS    N/A      N/A    84TS      32        176-5178
1027      AP9FS    N/A      N/A    84TS      32        N/A

[download]

There appears to be a significant column of information missing from the above table?

I could imagine that the above data represents the recommendations by the different manufacturers for the plugs in their range that would be applicable to two difference vehicles. Say the first is the normally aspirated version of some mark, and the second is the turbo-charged version. And whilst most of the manufacturers recommend the same plug for both, the BECK/ARNLEY plug is unsuitable for the latter variant. And, they have no suitable alternative in their range.

My point is, that whilst plugs from different manufacturers may be interchangable for a given vehicle, each manufacturers plugs have different ranges of operating parameters, which means that plugs from two different manufacturers are not interchangable for all applications.

The upshot is, the reason you are having so much trouble coming up with a normalisation schema, is because the key field--the vehicle--is missing from your table. Any attempt at normalisation based upon grouping of part numbers without taking the vehicle into consideration is at best doing your customers a dis-service. It could pursuade them to purchase plugs that are unsuitable for their particular vehicle, that might have limited life due to (say) overheating. Or worse, that could damage their engines by (say) holing their pistons by burning too hot.

At worst, it could be dangerous.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

In reply to Re^3: Organizing and presenting a cross-reference by BrowserUk
in thread Organizing and presenting a cross-reference by oko1

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