XML Schema Data Types

One of the biggest advantages XML Schema has over DTD is data types. DTD treats all content as text. XSD lets you declare that a price must be a decimal number, a date must follow the calendar format, and a quantity must be a positive integer. This prevents bad data from entering your system before processing even begins.

Two Categories of XSD Data Types

1. Simple Types

Simple types hold plain values — text, numbers, dates, booleans. They have no child elements and no attributes. Elements and attributes both use simple types.

2. Complex Types

Complex types contain child elements or attributes. They are covered in a separate topic. This page focuses entirely on simple types.

String Types

Type	Description	Example
xs:string	Any text, preserves all whitespace	Hello World
xs:normalizedString	Tabs and line breaks replaced with spaces	Hello World
xs:token	Normalized, leading/trailing spaces removed, internal spaces collapsed	Hello World
xs:Name	Valid XML name (letters, digits, hyphens, underscores)	product_id
xs:language	Language code per RFC 1766	en, hi, fr

Numeric Types

Type	Description	Example
xs:integer	Any whole number (positive or negative)	-5, 0, 42
xs:positiveInteger	Whole numbers greater than zero	1, 100, 9999
xs:negativeInteger	Whole numbers less than zero	-1, -50
xs:nonNegativeInteger	Zero and positive whole numbers	0, 1, 500
xs:nonPositiveInteger	Zero and negative whole numbers	0, -1, -200
xs:decimal	Any number with or without decimals	3.14, 299.99
xs:float	32-bit floating point number	3.14e2
xs:double	64-bit floating point number	3.141592653
xs:byte	Integer from -128 to 127	100
xs:short	Integer from -32768 to 32767	1000
xs:int	Integer from -2147483648 to 2147483647	50000
xs:long	Very large integer	9000000000

Date and Time Types

Type	Format	Example
xs:date	YYYY-MM-DD	2024-03-15
xs:time	HH:MM:SS	14:30:00
xs:dateTime	YYYY-MM-DDTHH:MM:SS	2024-03-15T14:30:00
xs:duration	PnYnMnDTnHnMnS	P1Y6M (1 year, 6 months)
xs:gYear	YYYY	2024
xs:gMonth	--MM	--03 (March)
xs:gDay	---DD	---15 (15th day)
xs:gYearMonth	YYYY-MM	2024-03

Other Useful Types

Type	Description	Example
xs:boolean	True or false value	true, false, 1, 0
xs:anyURI	A URL or URI	https://example.com
xs:base64Binary	Base64-encoded binary data	SGVsbG8=
xs:hexBinary	Hexadecimal binary data	48656C6C6F
xs:ID	Unique identifier in document	P001
xs:IDREF	Reference to an xs:ID	P001

Data Type Hierarchy Diagram

xs:anySimpleType
  |
  +-- xs:string
  |     |-- xs:normalizedString
  |     |     +-- xs:token
  |     |           +-- xs:language
  |     |           +-- xs:Name
  |     +-- xs:ID
  |     +-- xs:IDREF
  |
  +-- xs:decimal
  |     +-- xs:integer
  |           +-- xs:nonNegativeInteger
  |           |     +-- xs:positiveInteger
  |           |     +-- xs:unsignedLong → xs:unsignedInt → xs:unsignedShort → xs:unsignedByte
  |           +-- xs:nonPositiveInteger
  |                 +-- xs:negativeInteger
  |
  +-- xs:float
  +-- xs:double
  +-- xs:boolean
  +-- xs:date
  +-- xs:time
  +-- xs:dateTime
  +-- xs:anyURI

Using Data Types in a Schema

An online shopping order uses precise data types to prevent bad data:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:element name="order">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="orderID"    type="xs:positiveInteger"/>
        <xs:element name="orderDate"  type="xs:date"/>
        <xs:element name="customerName" type="xs:string"/>
        <xs:element name="totalAmount" type="xs:decimal"/>
        <xs:element name="isPaid"     type="xs:boolean"/>
        <xs:element name="deliveryURL" type="xs:anyURI" minOccurs="0"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

</xs:schema>

Valid XML

<order>
  <orderID>5001</orderID>
  <orderDate>2024-03-15</orderDate>
  <customerName>Divya Krishnan</customerName>
  <totalAmount>2349.50</totalAmount>
  <isPaid>true</isPaid>
  <deliveryURL>https://track.store.com/5001</deliveryURL>
</order>

Invalid XML — wrong data type

<order>
  <orderID>five thousand</orderID>  <!-- not a positiveInteger -->
  <orderDate>15-03-2024</orderDate>  <!-- wrong date format -->
  <isPaid>yes</isPaid>               <!-- not a boolean -->
</order>

Why Data Types Matter

A price stored as a string allows "free" or "call for price" to pass validation. A price stored as xs:decimal only allows numbers.
A date stored as xs:string allows "tomorrow" or "soon." A date stored as xs:date requires the exact YYYY-MM-DD format.
A quantity stored as xs:positiveInteger blocks zero and negative values automatically.

Key Points to Remember

XML Schema supports dozens of built-in data types for precise content control.
xs:string accepts any text; xs:integer accepts only whole numbers.
xs:date requires the YYYY-MM-DD format; xs:dateTime adds time after a T separator.
xs:boolean accepts true, false, 1, or 0.
xs:anyURI validates web addresses and URIs.
Data types prevent invalid data long before it reaches application logic.

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