XDM and Atomic Types

Every XPath value is a sequence of zero or more items, as the XQuery and XPath Data Model (XDM) defines it. An item is a node (one of seven kinds), an atomic value of an XML Schema type, or a function, which in 3.1 includes maps and arrays. A single item and a sequence of one item are the same thing.

Of the fifty or so built-in atomic types, the everyday ones are strings, xs:decimal (exact, for money) and its subtype xs:integer, xs:double, xs:boolean, dates, times, durations and xs:anyURI. Saxon 726,956 's adaptive output shows each value's type:

xp '42' '4.2e0' 'xs:date("2026-10-01")' 'map { "id": "b1" }' \
   'data(//book[1]/pages) instance of xs:untypedAtomic' '//book[1]/pages + 1'

42                                     => 42
4.2e0                                  => 4.2e0
xs:date("2026-10-01")                  => xs:date("2026-10-01")
map { "id": "b1" }                     => map{"id":"b1"}
data(//book[1]/pages) instance of xs:untypedAtomic => true()
//book[1]/pages + 1                    => 3.13e2

The last two lines matter most for data work: without a schema, an element's value is xs:untypedAtomic, text that becomes whatever type an operation demands, and arithmetic makes it an xs:double, so 312 pages plus one prints as 3.13e2. A schema-aware processor that validated the catalog against an XSD (Schema-Aware XSLT) would type pages as xs:integer; Saxon-HE is not schema-aware, so cast explicitly (Casting and Constructors).

Data Types

• item() — the root type for any single value in a sequence.
  • function(*) — any function item
  • node()
    • attribute()
    • comment()
    • document()
    • element()
    • namespace()
    • processing-instruction()
    • text()
  • xs:anyAtomicType
    • xs:error (a union type)
    • xs:untypedAtomic
    • xs:boolean
    • xs:base64Binary (e.g. AAAAFFFF, groups of 4-digit HEX)
    • xs:hexBinary (e.g. AF12, 4-digit HEX)
    • xs:anyURI
    • xs:QName (e.g. ab12, no symbol, no intermediate space)
    • xs:NOTATION
    • xs:numeric (a union type)
      • xs:float
      • xs:double
      • xs:decimal
        • xs:integer
          • xs:nonPositiveInteger
            • xs:negativeInteger
          • xs:long
            • xs:int
              • xs:short
                • xs:byte
          • xs:nonNegativeInteger
            • xs:positiveInteger
            • xs:unsignedLong
              • xs:unsignedInt
                • xs:unsignedShort
                  • xs:unsignedByte
    • xs:string
      • xs:normalizedString
        • xs:token (e.g. a b c 1 2 $%^&*&*&3)
          • xs:language (e.g. abc — no space, no symbol, no digit)
          • xs:NMTOKEN (e.g. abc123 — no space, no symbol)
          • xs:Name (e.g. abc — one leading space only, no symbol)
            • xs:NCName
              • xs:ID
              • xs:IDREF
              • xs:ENTITY
    • xs:gYearMonth (e.g. 2014-05)
    • xs:gYear (e.g. 2014)
    • xs:gMonthDay (e.g. --05-31)
    • xs:gDay (e.g. ---30)
    • xs:gMonth (e.g. --06)
    • xs:date (e.g. 2015-08-31)
    • xs:time (e.g. 18:30:30)
    • xs:dateTime (e.g. 2015-03-04T12:00:00)
      • xs:dateTimeStamp (e.g. 2015-03-04T12:00:00Z)
    • xs:duration (e.g. P1Y2M3D)
      • xs:yearMonthDuration (e.g. P1Y2M)
      • xs:dayTimeDuration (e.g. P10DT6H30M30S)

• xs:anyType — the root of the separate XSD type hierarchy.
  • user-defined complex types
  • xs:untyped
  • xs:anySimpleType
    • xs:IDREFS
    • xs:NMTOKENS
    • xs:ENTITIES
    • xs:anyAtomicType

Date and Time Examples

xs:numeric(true())

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