Atomic Types match atomics (JSON leaf values: strings, numbers, booleans, nulls).

Atomic Types have a lexical space (a set of literals denoting the values), a value space (a set of actual values), and a lexical mapping which maps the former into the latter.

An Atomic Type can be either the topmost atomic, or a primitive builtin type, or a builtin type derived from a primitive type, or a user-defined type derived from any other Atomic Type (except atomic).

A Derived Atomic Type can be defined by restricting the value space of another Atomic Type by specifying atomic facets. A restriction can also be made with the general facets $enumeration and $constraints.