Relational databases are based on the theory of relations as developed in set theory. Predicate calculus is often the most unambiguous way to express certain relational concepts. Occasionally this book uses the following predicate calculus notation to explain concepts.
|
This symbol … |
Represents this phrase … |
|
iff |
If and only if |
|
∀ |
For all |
|
∃ |
There exists |