IT Knowledge Base: Intensional and Extensional Documents

I ran across these terms while reading about Active XML. I wonder the correct meaning for these terms.

Quotes from scientists

When one door closes another door opens; but we so often look so long and so regretfully upon the closed door, that we do not see the ones which open for us. - Alexander Graham Bell
Physicists like to think that all you have to do is say, these are the conditions, now what happens next? - Richard Feynman
Yes, we have to divide up our time like that, between our politics and our equations. But to me our equations are far more important, for politics are only a matter of present concern. A mathematical equation stands forever. - Albert Einstein
The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane. - Nikola Tesla
Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas A. Edison
If I have ever made any valuable discoveries, it has been owing more to patient attention, than to any other talent. - Isaac Newton
Wonder is what sets us apart from other life forms. No other species wonders about the meaning of existence or the complexity of the universe or themselves. - Herbert W. Boyer
Philosophers say a great deal about what is absolutely necessary for science, and it is always, so far as one can see, rather naive, and probably wrong. - Richard Feynman

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