Scor­pio News


May 1989 – Volume 3. Final Issue.

Page 39 of 43

Inverse Requirements

Something not strictly Gemini related is the more recent Dave’s Law of Inverse Requirements. Now a few years ago I got involved in the design of a database system for document retrieval using microfilm, the earlier examples of which were written for the Gemini, but it soon became apparent that business customers were far more happy with IBM type computers, but that’s beside the point. Anyway, we rapidly decided that five fields would be manageable and entirely adequate, whilst more wouldn’t, apart from that, the required information would be on the microfilm, and the database was simply a tool to allow access to it. We also soon found out that the bigger the company the more fields they wanted. That figures, as always, some bright sparks in the company decided that management information could be accumulated in the databases, thus defeating the aim of the system in the first place as the management info was on the film.

This is where the Law comes into play. It states that the larger the customer, the more fields that say they require, but in practice, the fewer fields they ultimately use. BAA wanted 13 fields – they insisted, and grumbled loudly when we asked, ‘What for ?’. They finally agreed to give it a go with the 5 fields supplied, with the rider that they would expect the number of fields to be expanded or they could sling it back and get their money back. You guessed it, the database is still growing after 3 years at 15,000 entries a month, using one field of 12 characters. Several other customers have exhibited the same behaviour. Strange isn’t it ?

I read an article once about the Great Murphy and how his Laws affect instrumentation engineers. The only one I remember was one about having dismantled and re-assembled a instrument, there would always be one nut and bolt left over. Any one who’s taken a car engine apart will know the feeling and will be lucky if it’s only one nut and bolt. None the less, the corollary was that having taken the instrument apart again to fit the missing nut and bolt, it will be discovered that nothing was missing in the first place, and that the nut and bolt came from one of the several instruments which was serviced yesterday. Oh I know, having dismantled and re-assembled many disk drives in my time – the number of times that particular Law has held true.

A couple of pages worth. Paul said don’t make it too long or he’d cut it, so I’d better stop here with one passing thought. Today is Sunday, and this afternoon I have done something nasty to my back. Having very painfully sat down at the computer, I now can’t get out of the chair. My brother says it’s good for a couple of weeks off work, and I guess the doctor will say the same tomorrow. But I’m on holiday next week. That’s Murphy for you, why can’t I be sick in the firm’s time ?

Oh yes, the answer to the question of the day, simple – it can’t be done, it’s a hardware problem !!

Page 39 of 43