15.2.14. XSD indicator

With indicators, we can control how elements are used in the document.

Indicator ¶

There are seven indicators:

Order indicator:

All
Choice
Sequence

Occurrence indicator:

MaxOccurs
MinOccurs

Group indicator:

Group name
AttributeGroup name

Order indicator ¶

The Order indicator is used to define the order of elements.

All indicator ¶

The < all > indicator states 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>

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

Choice indicator ¶

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

<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 indicator ¶

The Occurrence indicator is used to define how often an element occurs.

注意： For all “Order” and “Group” indicators (any, all, choice, sequence, group name, and group reference), the default values for maxOccurs and minOccurs are 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 shows that the child element “child_name” can appear at least once in the “person” element (where the default value for minOccurs is 1) and up to 10 times.

MinOccurs indicator ¶

The < minOccurs > indicator specifies 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 shows that the child element “child_name” can appear at least 0 times and up to 10 times in the “person” element.

提示： To make the occurrence of an element unlimited, use the declaration maxOccurs= “unbounded”:

A practical example: ¶

A 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 above XML file contains a root element named “persons”. Within 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.

这是schema文件”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 indicator ¶

The Group indicator is used to define related batches of elements.

Element group ¶

Element groups are defined through group declarations:

<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 a precise order:

<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>

After you have defined 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 group ¶

Property groups are defined through attributeGroup declarations:

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

The following example defines a property group named “personattrgroup”:

<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>

After you have defined the property 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>