XSD Indicators

Through indicators, we can control the way elements are used in a document.

Indicators

There are seven types of indicators:

Order Indicators:

All
Choice
Sequence

Occurrence Indicators:

maxOccurs
minOccurs

Group Indicators:

Group name
attributeGroup name

Order Indicators

Order indicators are used to define the order of elements.

All Indicator

The <all> indicator specifies that child elements can appear in any order, and each child element must appear only once:

<xs:element name="person">
<xs:complexType>
    <xs:all>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
    </xs:all>
</xs:complexType>
</xs:element>

Note:When using the <all> indicator, you can set <minOccurs> to 0 or 1, and you can only set the <maxOccurs> indicator to 1 (<minOccurs> and <maxOccurs> will be explained later).

Choice Indicator

The <choice> indicator specifies that either one child element or another child element can appear (either/or):

<xs:element name="person">
<xs:complexType>
    <xs:choice>
      <xs:element name="employee" type="employee"/>
      <xs:element name="member" type="member"/>
    </xs:choice>
</xs:complexType>
</xs:element>

Sequence Indicator

<sequence> specifies that child elements must appear in a specific order:

<xs:element name="person">
   <xs:complexType>
    <xs:sequence>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
    </xs:sequence>
</xs:complexType>
</xs:element>

Occurrence Indicators

Occurrence indicators are used to define how often an element can appear.

Note:For all "Order" and "Group" indicators (any, all, choice, sequence, group name, and group reference), the default values of maxOccurs and minOccurs are both 1.

maxOccurs Indicator

The <maxOccurs> indicator can specify the maximum number of times an element can appear:

<xs:element name="person">
<xs:complexType>
    <xs:sequence>
      <xs:element name="full_name" type="xs:string"/>
      <xs:element name="child_name" type="xs:string" maxOccurs="10"/>
    </xs:sequence>
</xs:complexType>
</xs:element>

The above example indicates that the child element "child_name" can appear at least once in the "person" element (where the default value of minOccurs is 1) and at most 10 times.

minOccurs Indicator

The <minOccurs> indicator can specify the minimum number of times an element can appear:

<xs:element name="person">
<xs:complexType>
    <xs:sequence>
      <xs:element name="full_name" type="xs:string"/>
      <xs:element name="child_name" type="xs:string"
      maxOccurs="10" minOccurs="0"/>
    </xs:sequence>
</xs:complexType>
</xs:element>

The above example indicates that the child element "child_name" can appear at least 0 times and at most 10 times in the "person" element.

Tip:If you want an element to have unlimited occurrences, use the declaration maxOccurs="unbounded":

A practical example:

An XML file named "Myfamily.xml":

<?xml version="1.0" encoding="ISO-8859-1"?>

<persons xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="family.xsd">

<person>
<full_name>Hege Refsnes</full_name>
<child_name>Cecilie</child_name>
</person>

<person>
<full_name>Tove Refsnes</full_name>
<child_name>Hege</child_name>
<child_name>Stale</child_name>
<child_name>Jim</child_name>
<child_name>Borge</child_name>
</person>

<person>
<full_name>Stale Refsnes</full_name>
</person>

</persons>

The XML file above contains a root element named "persons". Inside this root element, we define three "person" elements. Each "person" element must contain a "full_name" element, and it can contain up to 5 "child_name" elements.

This is the schema file "family.xsd":

<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified">

<xs:element name="persons">
<xs:complexType>
    <xs:sequence>
      <xs:element name="person" maxOccurs="unbounded">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="full_name" type="xs:string"/>
            <xs:element name="child_name" type="xs:string"
            minOccurs="0" maxOccurs="5"/>
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
</xs:complexType>
</xs:element>

</xs:schema>

Group Indicators

Group indicators are used to define related sets of elements.

Element Groups

Element groups are defined using the group declaration:

<xs:group name="groupname">
...
</xs:group>

You must define an all, choice, or sequence element inside the group declaration. The following example defines a group named "persongroup", which defines a set of elements that must appear in an exact order:

After you have defined the group, you can reference it in another definition:

<xs:group name="persongroup">
<xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
    <xs:element name="birthday" type="xs:date"/>
</xs:sequence>
</xs:group>

<xs:element name="person" type="personinfo"/>

<xs:complexType name="personinfo">
<xs:sequence>
    <xs:group ref="persongroup"/>
    <xs:element name="country" type="xs:string"/>
</xs:sequence>
</xs:complexType>

Attribute Groups

Attribute groups are defined using the attributeGroup declaration:

<xs:attributeGroup name="groupname">
...
</xs:attributeGroup>

The following example defines an attribute group named "personattrgroup":

After you have defined the attribute group, you can reference it in another definition, like this:

<xs:attributeGroup name="personattrgroup">
<xs:attribute name="firstname" type="xs:string"/>
<xs:attribute name="lastname" type="xs:string"/>
<xs:attribute name="birthday" type="xs:date"/>
</xs:attributeGroup>

<xs:element name="person">
<xs:complexType>
<xs:attributeGroup ref="personattrgroup"/>
</xs:complexType>
</xs:element>

Other Extensions