I think Albert doesn't understand the state of his own mind let alone the state of data.
Albert,
What is domain of attribute (column) "AGE" in an employees table?
I'd say 18-65 ages. If a scalar is UNKNOWN, is it "totally unknown" or
just "partially unknown"? I'd say partially, since we exactly know that
250 years old man cannot be an employee in our company.
You said:
The problem with your explanation here is that you are mixing database level concepts and business level concepts. Just because you create a column on your database that is called age, this will simply be a numeric datatype. The database has no concept of what "age" is and doesn't know that 250 would be an unreasonable value. The domain of reasonable values is something that is determined by business logic that is applied at a level above the database level. As far as the database is concerned if a value isn't entered for the age then it is just "unknown", not "partially unknown" or "totally unknown", just plain old "unknown". You obviously have some understanding of programming concepts but obviously a total lack of understanding or confusion when it comes to systems design concepts.
I'd really be happy to convince you that I DON'T THINK that you don't understand the state of YOUR mind. I really DON'T THINK that. I KNOW that. And I'm going to explain this to you. Just consider an example from yesterday, not yours, but very illustrative to show that the overall confusion on this thread is constantly being made by people who don't understand what they are talking about .
Sundar M:
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I'd say that (x - x) is always zero regardless of whether x is KNOWN or UNKNOWN
Suppose x is ∞, Would you say infinity(∞) - ∞ is zero?
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I answerd:
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Saying "x is infinity" is wrong. We can say then
LIMIT (x - x) = 0
x -> ∞
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Sundar M:
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Well, you can argue with this guy.
http://www.netscape.com/viewstory/2007/01/07/math-proof-infinity-subtracted-from-infinity-does-not-equal-to-zero/?url=http%3A%2F%2Fwww.philforhumanity.com%2FInfinity_Minus_Infinity.html++&frame=true
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I answerd:
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I've just done it. Guy is OK. Here is his conclusion:
"Woops! It is impossible for infinity subtracted from infinity to be equal to one and zero. Using
this type of math, we can get infinity minus infinity to equal any real number. Therefore, infinity
subtracted from infinity is undefined."
Hence we should write the equation as I've already shown:
LIMIT (x - x) = 0
x-> oo
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As you see, the person, who knows NOTHING about Infinitesimal and Integral theory and calculus was trying to force discussion about it, and, of course, fell short of it - own pitfall (trap). The only result: the thread was expanded with 2 additional petties and nonsenses. Total confusion.
So, please, don't do the same.
I was not talking about database level concepts and business level concepts. And therefore I couldn't mixed them. I know that a database (software) cannot guess our thoughts. What I was talking about has nothing to do with it. So, please!
Regards
Albert