Reading Comphernsive - schema meaning

shahar

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What is the meaning of the word schema in this passage:
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In Wikipedia, Page "Relational Algebra" in link:

I think it could besubstitute with the word "formula". Am I right?!
 
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More question that is in similar topic but off topic.
Can I use the word set inside of tuple, or more precisely set of variable so:
tuple = set ?
 
You mean "instead of", not "inside of".

To answer the question, no, a set has no order; a tuple is ordered. That is, the sets {1, 2} and {2, 1} are the same set; the (ordered) 2-tuples (1, 2) and (2, 1) are not. I suppose we have to ask the question, do we ever talk about unordered n-tuples? Wikipedia says no. (I notice the introduction there ends with the definition used in relational databases, which is apparently your context; there, each entry is in a distinct column, which is the same idea as ordering.)

As for your first question, I can't imagine that could be called a formula; on the other hand, it's unfortunate that the article doesn't define what it means by "schema", which doesn't seem to fit any usage I find. If anything, they seem to be using "schema" to mean an n-tuple of attributes.
 
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