Editing XPath 2.0 (section)

== Type system ==
[[File:XQuery and XPath Data Model type hierarchy.png|thumb|The [[XQuery and XPath Data Model|XDM]] type hierarchy]]
The type system of XPath 2.0 is noteworthy for the fact that it mixes [[strong typing]] and [[weak typing]] within a single language.

Operations such as arithmetic and boolean comparison require atomic values as their operands. If an operand returns a node (for example, <code>@price * 1.2</code>), then the node is automatically ''atomized'' to extract the atomic value. If the input document has been validated against a schema, then the node will typically have a type annotation, and this determines the type of the resulting atomic value (in this example, the <code>price</code> attribute might have the type <code>decimal</code>). If no schema is in use, the node will be untyped, and the type of the resulting atomic value will be <code>untypedAtomic</code>. Typed atomic values are checked to ensure that they have an appropriate type for the context where they are used: for example, it is not possible to multiply a date by a number. Untyped atomic values, by contrast, follow a weak typing discipline: they are automatically converted to a type appropriate to the operation where they are used: for example with an arithmetic operation an untyped atomic value is converted to the type <code>double</code>.