Hello, Voblin, you wrote: EP>> data structures - too mathematics... V> we Take for an example database designing. We take the functional requirements and it is transformed them into a dial-up of entities and communications. There is there a mathematics? Somewhere there in depth, of course, yes, but it is is specific at the moment of designing of basis we it we are not soared at all. We are soared by, whether correctly we understood data domain. And it any more mathematics, and accounts department, office-work and other "lyrics". Also we are still soared by that to us the potential user forgot to tell. It too not the mathematics, and is faster psychology. We imagine crowd mentally not outstanding users and we try to estimate, as the system of moves, if instead of a normal use-case in their heads in the image any perversion. It too not the mathematics, and is faster social psychology. Especially that its section in which the broken windows are studied. V> Yes, the database structure is a technical application of predicate calculus, which unambiguously mathematics. But at designing of structure we at all are not engaged in this mathematics. We are engaged in everything, but only not mathematics. Are engaged, including mathematics. If to be able to think only of users - that is banal it turns out nothing - besides it it is necessary also to understand as it is all mechanically works, what mechanical glue all it communicates, to be able to apply and change all this abstract mechanics. That who thinks ONLY of users and "other office-work" is a customer, instead of the engineer or the designer. Even if not to know mathematical terms, and to name and use all these small screws and somehow in own way, intuitively - that it all the same the mathematician - rigid, abstract, mechanical system. Addition does not cease to be addition from that that adding does not know this word.