XQuery

The Built-in Types

A wide array of atomic types is built into XQuery. These simple types, shown in Figure 11-1, represent common datatypes such as strings, numbers, dates, and times. The built-in types are identified by qualified names that are prefixed with xs, because they are defined in the XML Schema Namespace. You can use all of these built-in types in your queries whether or not the implementation is actually schema-aware, and whether or not you are using schemas to validate your source or result documents.

Figure 11-1. The atomic type hierarchy

Nineteen of the built-in types are primitive, meaning that they are the top level of the type hierarchy. Each primitive type has a value space, which describes all its valid values, and a set of lexical representations for each value in the value space. There is one lexical representation, the canonical representation, that maps one-to-one with each value in the value space. The canonical representation is important because it is the format used when a value is serialized or cast as a string.^[*]

For example, the primitive type xs:integer has a value that is equal to 12 in its value space. This value has multiple lexical representations that map to the same value, such as 12, +12, and 012. The canonical representation is 12. Some primitive types, such as xs:date, only have one lexical representation, which becomes, by default, the ...