XML Schema Complete Reference, The

6.7. Simple Types

A simple type specifies a value range. An element type or attribute type may specify a simple type to impose a range of values on a corresponding XML instance. In the simplest case, a built-in datatype imposes the value range. Frequently, a simple type derived from a built-in datatype provides further constraints. A constraining facet on the derived simple type specifies a restriction of the value range. Multiple constraining facets may apply to a single simple type.

6.7.1. Built-in Datatypes

The built-in datatypes fall mostly into three categories: strings, numbers, and dates. Each of these categories has multiple specific datatypes. For example, a date might or might not include the time. Alternatively, perhaps the only ...