XML Schema Simple Types

XML Schema Simple Types are fundamental building blocks in XML Schema that define the content and constraints for individual elements or attributes in an XML document. They provide a way to specify the data type, format, and restrictions for values in XML elements.

Purpose and Role

Simple types serve several crucial functions in XML Schema:

• Define data types for element content and attribute values
• Enforce data validation rules
• Restrict the range of acceptable values
• Ensure consistency and integrity of XML data

Basic Syntax and Usage

To define a simple type in XML Schema, use the <xs:simpleType> element. You can then specify restrictions using various facets.

<xs:simpleType name="ageType">
  <xs:restriction base="xs:integer">
    <xs:minInclusive value="0"/>
    <xs:maxInclusive value="120"/>
  </xs:restriction>
</xs:simpleType>

This example defines a simple type named "ageType" that restricts the value to integers between 0 and 120.

Common Use Cases

XML Schema Simple Types are widely used for various purposes:

1. Defining Custom Data Types

Create specific data types tailored to your application's needs.

<xs:simpleType name="USStateCode">
  <xs:restriction base="xs:string">
    <xs:pattern value="[A-Z]{2}"/>
  </xs:restriction>
</xs:simpleType>

2. Enforcing Value Constraints

Set limitations on acceptable values for elements or attributes.

<xs:simpleType name="percentageType">
  <xs:restriction base="xs:decimal">
    <xs:minInclusive value="0"/>
    <xs:maxInclusive value="100"/>
  </xs:restriction>
</xs:simpleType>

Important Considerations

• Choose appropriate base types for your simple types
• Use restrictions judiciously to maintain data integrity
• Consider reusability when defining custom simple types
• Document your simple types for better maintainability

Built-in Simple Types

XML Schema provides numerous built-in simple types. Some commonly used ones include:

Type	Description
xs:string	Represents character strings
xs:integer	Represents whole numbers
xs:decimal	Represents decimal numbers
xs:date	Represents dates (YYYY-MM-DD)
xs:boolean	Represents true/false values

Conclusion

XML Schema Simple Types are essential for defining and constraining data in XML documents. By mastering their usage, you can create more robust and reliable XML schemas, ensuring data consistency and validity across your XML-based applications.

For more advanced topics, explore XML Schema Complex Types and XML Schema Elements.