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16.6. Simple Content

Earlier, the xs:simpleContent element was used to declare an element that could only contain simple content:

<xs:element name="fullName">
      <xs:extension base="xs:string">
        <xs:attribute name="language" type="xs:language"/>

The base type for the extension in this case was the built-in xs:string data type. But simple types are not limited to the predefined types. The xs:simpleType element can define new simple data types, which can be referenced by element and attribute declarations within the schema.

16.6.2. Facets

In schema-speak, a facet is an aspect of a possible value for a simple data type. Depending on the base type, some facets make more sense than others. For example, a numeric data type can be restricted by the minimum and maximum possible values it could contain. But these types of restrictions wouldn't make sense for a boolean value. The following list covers the different facet types that are supported by a schema processor:

  • length (or minLength and maxLength)

  • pattern

  • enumeration

  • whiteSpace

  • maxInclusive and maxExclusive

  • minInclusive and minExclusive

  • totalDigits

  • fractionDigits

Facets are applied to simple types using the xs:restriction element. Each facet is expressed as a distinct element within the restriction block, and multiple facets can be combined to further restrict potential values of the simple type. Numeric Facets

Almost half of the of built-in data types defined by the schema specification represent numeric data of one type or another. More might be called numeric since the date/time and duration types are considered to be scalar quantities as well. The following two sections cover all of the numeric facets available, but for a comprehensive list of which of these facets are applicable to which data types, see Chapter 21.

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