"string" Datatype Values and Representations

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∟"string" Datatype Values and Representations

This section describes the most commonly used built-in datatype, 'string'. Whitespace characters are preserved in 'string' values. But XML entity references are parsed in 'string' lexical representations.

The "string" datatype and its derived datatypes are the most commonly used built-in datatypes in XML documents. Let's take a closer look at the "string" datatype first.

"string" is a primitive datatype with a value set of all possible sequences of Unicode characters. A "string" value can be expressed in an XML document using a sequence of characters.

Parsed XML entity references are allowed in "string" lexical representations. But they will be parsed to obtain final "string" values. For example, 3 XML elements below are all valid and represent the same "string" value:

    <String>PI &gt; 3.14159</String>
    <String>PI > 3.14159</String>
    <String><![CDATA[PI > 3.14159]]></String>

Another note on "string" values is that whitespace characters, '\t', '\r', '\n' and ' ', are preserved in "string" values. For example, 3 XML elements below are all valid and represent 3 different "string" values:

    <String>Herong Yang</String>
    <String>Herong
Yang</String>
    <String>Herong
            Yang</String>

A close example of using "string" datatype in XML is the <PRE> element in HTML documents, where all whitespace characters are preserved.

Here is a sample XSD document that defines a sub element <String> to use "string" values:

<?xml version="1.0"?>
<!-- string_datatype_test.xsd
 - Copyright (c) 2002-2013 HerongYang.com. All Rights Reserved.
-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="String_Datatype_Test">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="String" type="xs:string"
        maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>
</xs:schema>

Here is a sample XML document that contains <String> elements to test this XSD document:

<?xml version="1.1"?>
<!-- string_datatype_test.xml
 - Copyright (c) 2002-2013 HerongYang.com. All Rights Reserved.
-->
<String_Datatype_Test>
<!-- 3 valid "string" elements represent the same value -->
  <String>PI &gt; 3.14159</String>
  <String>PI > 3.14159</String>
  <String><![CDATA[PI > 3.14159]]></String>

<!-- 3 valid "string" elements represent different values -->
  <String>Herong Yang</String>
  <String>Herong
Yang</String>
  <String>Herong
          Yang</String>

<!-- 1 invalid "string" elements -->
  <String> Hello <b>Herong</b>! </String>
</String_Datatype_Test>

Compile and run XsdSchemaValidator.java. You see 1 error on the invalid "string" element:

herong> java XsdSchemaValidator
^^^string_datatype_test.xsd string_datatype_test.xml

Error:
   Line number: 19
   Column number: 42
   Message: cvc-type.3.1.2: Element 'String' is a simple type, so it
   must have no element information item [children].

Failed with errors: 1