A type is a set of permissible values. The type integer is {-32000,…,-1,0,+1,32000}.
It is common and advantageous practice in programming to type constants and variables.
But typing tells us more:
- Structure (what we expect to find in it).
- Behaviour (what we expect to use in it).
- A basis for type checking.
- Is an expression type correct?
Basic primitive types:
- Integer
- Real
- Character
- String
- Boolean.
Type constructors e.g. array.
SQL has DDL, DML and a little of RDL.






