Requirements vs. specifications – an analogy

To illustrate my earlier post, and continuing the theme of teaching grandmothers to suck eggs, consider this analogy between buying a car and an application software package.

Joe goes into a number of car showrooms – he explains to the salesmen that he’s looking for a car for his family of four. He wants a fast car, one that’s reasonably economical, and he has a budget of £15,000. After viewing some of the cars, he takes a test drive in one which he likes – it accelerates fast and reaches 70 mph quickly, has two doors and four good seats, the salesman says it returns 30 mpg, and it only costs £14,000 with a manual gearbox. He asks about accessories, adds in a roof box and a towing bracket, and leaves the showroom with a quotation and a copy of the brochure for the car. On his way home he sees that several of his neighbours have purchased the same model of car, but doesn't speak to any of them about their cars.

After a quick discussion with his wife Joe decides to buy the car, it is duly delivered and after a couple of weeks he returns to the showroom complaining that with the roof box in place he’s not getting 30 mpg, and when he tows the caravan, he’s not getting the acceleration nor the speed that he expected. Even worse, his two 6ft teenagers can’t get into the back seats easily, and his wife can’t drive it because she can only drive automatics.

The garage quickly falls back on its contract of supply – which is against the specification included in the brochure supplied with the quotation – and which specifies the conditions for the quoted fuel consumption and performance, and included measurements of the rear seat sizes and doors. The fault lies with Joe - a purchaser who failed to involve all the users (his wife and children), failed to define fully his requirements (his family and the caravan), and failed to check the specifications contained in the brochure before he ordered the car. He also failed to recognise that if you use a product in a non-standard way or change the specification (e.g. adding a roof box, or towing a caravan), it can dramatically change the expectations of how the product will perform.

The car salesman does however, point out to Joe that there is a 4-door version of the car, with a bigger engine and automatic gearbox, that would tow the caravan easily – and an estate version that would remove the need for the roof box. However, it costs £20,000 and is not so economical to run.

So Joe decides to live with his new car........