Is there a way to enforce/preserve order of XML elements in an XML Schema?
- by MarcoS
Let's consider the following XML Schema:
<?xml version="1.0" encoding="UTF-8"?>
<schema
targetNamespace="http://www.example.org/library"
elementFormDefault="qualified"
xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:lib="http://www.example.org/library">
<element name="library" type="lib:libraryType"></element>
<complexType name="libraryType">
<sequence>
<element name="books" type="lib:booksType"></element>
</sequence>
</complexType>
<complexType name="booksType">
<sequence>
<element name="book" type="lib:bookType"
maxOccurs="unbounded" minOccurs="1"></element>
</sequence>
</complexType>
<complexType name="bookType">
<attribute name="title" type="string"></attribute>
</complexType>
</schema>
and a corresponding XML example:
<?xml version="1.0" encoding="UTF-8"?>
<lib:library
xmlns:lib="http://www.example.org/library"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.example.org/library src/library.xsd ">
<lib:books>
<lib:book title="t1"/>
<lib:book title="t2"/>
<lib:book title="t3"/>
</lib:books>
</lib:library>
Is there a way to guarantee that the order of <lib:book .../> elements is preserved? I want to be sure that any parser reading the XML will return books in the specified oder, that is first the book with title="t1", then the book with title="t2", and finally the book with title="t3".
As far as I know XML parsers are not required to preserve order. I wonder whether one can enforce this through XML Schema? One quick solution for me would be adding an index attribute to the <lib:book .../> element, and delegate order preservation to the application reading the XML.
Comments? Suggestions?
