The unsignedLong data type is derived from the nonNegativeInteger type. : unsignedLong « XML Schema « XML Tutorial

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The value space is the set of integers greater than or equal to 0 and less than or equal to 18446744073709551615. 
The lexical space is a finite-length sequence of decimal digits.

<!-- schema -->
<xsd:simpleType name="distance_sun">
  <xsd:restriction base="xsd:unsignedLong">
   <xsd:pattern value="\d{8}"/>
  </xsd:restriction>
</xsd:simpleType>

<!-- instance document -->
<distance_sun>939000000</distance_sun>