RE: modeling, validating and documenting an xml grammar
All working systems are particular cases. General cases apply to general systems, but I find none of these. That's just the hissy way of saying, 'can' did not equal 'does' in my response. I am aware of the work of Codd et al, but also that mathematical proof is seldom required in a demonstration for a BAFO, but speed always is. Apart from performance issues which one can claim are not impacted, but which do depend on particular cases and particular implementations, what one expects of the engineers is that in cases of denormalization, there are no relationships being violated and no business rules or policies being violated. That is, for example in databases we build, it is important to have the name of the criminal or the business in the names table, but not necessarily their doctor or lawyer. Yes, that can result in an undetectable relationship but policy being what it is, until they become one of the two cited, they are not in the names tables. The same is true of agency employees. len From: Rick Marshall [mailto:rjm@z...] with all due respect len, this argument was dealt with comprehensively about 30 years ago. databases that aren't fully normalised will always be more efficient in particular cases, but not in the general case. moreover there's no mathematical proof of correctness when things aren't nomalised, whereas there is when they are. however there are considerable performance issues surrounding the optimisers in many of the popular rdbms's and their sql implemenations. nevertheless, the case in point here is how to support two simultaneous tree views. xml supports one easily, as in eg orders and the lines on the orders. but what if you want a second that is products and the orders they are on. one is quick and efficient, the other is very slow. but we discussed this in detail a long time ago. rick
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