XML Schema Indicators

From http://www.w3schools.com (Copyright Refsnes Data)

# XSD Complex Types Indicators

We can control HOW elements are to be used in documents with indicators.

## Indicators

There are seven 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 the elements.

All Indicator

The <all> indicator specifies that the child elements can appear in any order, and that each child element must occur 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 the <minOccurs> indicator to 0 or 1 and the <maxOccurs> indicator can only be set to 1 (the <minOccurs> and <maxOccurs> are described later).

Choice Indicator

The <choice> indicator specifies that either one child element or another can occur:

    <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

The <sequence> indicator specifies that the 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 occur.

Note: For all "Order" and "Group" indicators (any, all, choice, sequence, group name, and group reference) the default value for maxOccurs and minOccurs is 1.

maxOccurs Indicator

The <maxOccurs> indicator specifies the maximum number of times an element can occur:

    <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 example above indicates that the "child_name" element can occur a minimum of one time (the default value for minOccurs is 1) and a maximum of ten times in the "person" element.

minOccurs Indicator

The <minOccurs> indicator specifies the minimum number of times an element can occur:

    <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 example above indicates that the "child_name" element can occur a minimum of zero times and a maximum of ten times in the "person" element.

Tip: To allow an element to appear an unlimited number of times, use the maxOccurs="unbounded" statement:

A working example:

An XML file called "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 have defined three "person" elements. Each "person" element must contain a "full_name" element and it can contain up to five "child_name" elements.

Here 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 with the group declaration, like this:

    <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", that defines a group of elements that must occur in an exact sequence:

    <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 a group, you can reference it in another definition, like this:

    <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 with the attributeGroup declaration, like this:

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

The following example defines an attribute 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 an 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>

From http://www.w3schools.com (Copyright Refsnes Data)