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 document uses the following predicate calculus and set theory notation to explain concepts.
| This symbol … | Represents this phrase … |
|---|---|
| Predicate Calculus Notation | |
| iff | If and only if |
| ∀ | For all |
| ∃ | There exists |
| Set Theory Notation | |
∅ |
Empty set |
| ∪ | Union |
| ∩ | Intersection |
| ℵ | Infinitely large set Pronounced "aleph" |