Set Theory
Itzik Ben-Gan is one of this book’s authors. That’s a fact, and database systems like SQL Server 2008 help us identify facts and separate them from fiction. Here are some other facts about who is and who isn’t one of this book’s authors: Dejan Sarka is one; Bill Gates is not.
In the language of sets, we can describe the set of authors of this book, and we can use the language of set theory to express facts.
If we name the set of authors of this book A, we can write A = {Itzik Ben-Gan, Lubor Kollar, Dejan Sarka, Steve Kass}. We call A a set, and we call the four authors elements, or members, of A. The statement that Itzik is one of the book’s authors can be expressed as Itzik∈A.
Note
As we’ll soon see, there should always be some universal ...
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