Question

I am facing an issue with an XML Schema. I would like to introduce elements into another element which has been defined to be recursive.

The above lines of code are meant to represent file and folders.

Here is the current code:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"
    xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning" vc:minVersion="1.1"> 

    <xs:complexType name="folder_type">
        <xs:sequence minOccurs="0" maxOccurs="unbounded">
            <xs:element name="folder" type="folder_type"></xs:element>
        </xs:sequence>
        <xs:attribute name="name" type="xs:string" use="required"></xs:attribute>
    </xs:complexType>

    <xs:element name="filefoldertree">
        <xs:complexType>
            <xs:sequence minOccurs="0" maxOccurs="unbounded">
                <xs:element name="folder" type="folder_type"></xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

For instance, the above XSD code allows me to define the following XML lines:

<filefoldertree xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="file:/C:/Users/Hadi/Desktop/filefoldertree.xsd">

    <folder name="a">
        <folder name="b">
            <folder name="c">
            </folder>
        </folder>
    </folder>
    <folder name="d">
    </folder>
</filefoldertree>

Until there, this is a desirable behavior. However I would like to add a sequence of file elements, nested in the folder one. For example, I am seeking for the following result:

    <folder name="a">
        <folder name="b">
            <file attr1="x" attr2="y" attr3="z"></file>
            <folder name="c">
                <file attr1="x" attr2="y" attr3="z"></file>
            </folder>
        </folder>
    </folder>
    <folder name="d">
        <file attr1="x" attr2="y" attr3="z"></file>
    </folder>
    <file attr1="x" attr2="y" attr3="z"></file>

Since folder is a typed element, I cannot define a nested complextype, however I need its recursive functionality.

How to modify the XSD code in order to achieve the behavior illustrated by the code above?

Thank you for your answers.

Answer 1

You can use xs:choice in a recursive type declaration as follows:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           elementFormDefault="qualified">

  <xs:element name="filefoldertree" type="FolderType"/>

  <xs:complexType name="FolderType">
    <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="folder" type="FolderType"/>
      <xs:element name="file" type="FileType"/>
    </xs:choice>
    <xs:attribute name="name" type="xs:string" use="required"/>
  </xs:complexType>

  <xs:complexType name="FileType">
    <xs:sequence/>
    <xs:attribute name="name" type="xs:string" use="required"/>
  </xs:complexType>

</xs:schema>

Note: You might want to name the top-level element folder rather than the one-off, filefoldertree.

XSD elements inside a recursive defined element

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