How xs:totalDigits Restricts XML Numeric Precision

The xs:totalDigits facet in XML Schema Definition (XSD) restricts the absolute precision of a numeric data type by defining the maximum number of decimal digits permitted. This article explains how xs:totalDigits operates, which data types it applies to, how it handles both integer and fractional components, and how it pairs with other facets like xs:fractionDigits to enforce strict data validation rules.

How xs:totalDigits Works

The xs:totalDigits facet places an upper limit on the total count of digits in a numeric value. This count includes all digits present in both the integer part (before the decimal point) and the fractional part (after the decimal point).

• Applicable Types: It applies to xs:decimal and all built-in types derived from it, including xs:integer, xs:long, xs:int, xs:short, xs:byte, and non-negative/positive variants. It does not apply to xs:float or xs:double, which follow IEEE floating-point representations.
• Facet Value Requirement: The value assigned to xs:totalDigits must be a positive integer (xs:positiveInteger), meaning it must be greater than zero.
• Zero Handling: Leading zeros before the whole number and trailing zeros after a decimal point (which do not alter the mathematical value) are generally normalized during validation, but any significant digit contributes toward the limit.

Example Usage in XSD

The following schema defines a custom type for a price element that allows a maximum of 5 total digits:

<xs:simpleType name="PriceType">
  <xs:restriction base="xs:decimal">
    <xs:totalDigits value="5"/>
  </xs:restriction>
</xs:simpleType>

Valid Values

• 12345 (5 integer digits, 0 fractional digits = 5 total)
• 123.45 (3 integer digits, 2 fractional digits = 5 total)
• 1.2 (1 integer digit, 1 fractional digit = 2 total)
• 0.1234 (0 leading non-zero digits, 4 fractional digits = 4 total)

Invalid Values

• 123456 (6 digits exceeds the limit of 5)
• 1234.56 (6 total digits exceeds the limit of 5)
• 0.123456 (6 fractional digits exceeds the limit of 5)

Interaction with xs:fractionDigits

xs:totalDigits is frequently combined with xs:fractionDigits to control exact structural formatting for financial or measurement data:

<xs:simpleType name="MonetaryAmount">
  <xs:restriction base="xs:decimal">
    <xs:totalDigits value="7"/>
    <xs:fractionDigits value="2"/>
  </xs:restriction>
</xs:simpleType>

In this configuration: * xs:totalDigits="7" sets the total precision ceiling to 7 digits. * xs:fractionDigits="2" restricts the fractional component to a maximum of 2 digits. * Consequently, the integer portion cannot exceed 5 digits (7 total digits minus 2 fractional digits). * A value like 12345.67 is valid, whereas 123456.7 (6 integer digits + 1 fraction digit = 7 total) is valid under total digits, but 123456.78 (8 total digits) will fail schema validation.