[Erlich_Bachman]

Being able to refer to my car, or ship, or other vessel, as an identified single object, regardless of what parts have been changed - yes, I would say it is very useful thing for living with it and operating it.

> easy to copy and to rember

That's a very important, useful and valueable property of an abstraction, yes. Though certainly not the only important property.

Or do you want one that takes you hours to understand and that you have to remind yourself of it and re-learn every week?