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Indicators In XSD

In this tutorial I will explain about indicators in XSD. Indicator in XSD is the way how elements are organized in XML. There are three categories of indicators

Order indicator
1. All
2. Choice
3. Sequence
Occurrence indicator
1. minOccurs
2. maxOccurs
Group indicator
1. Element group
2. Attribute group

Let us discuss about each indicator

All

It means that elements can occur in any order in XML. Consider the following XSD

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="person">
		<complexType>
			<all>
				<element name="Section" type="string"/>
				<element name="name" type="string"/>
			</all>
		</complexType>
	</element>
</schema>

Here the elements ‘Section’ and ‘name’ can occur in any order in XML. So for this XSD both XMLs are fine.

<person>
	<name>Karan</name>
	<Section>E</Section>
</person>

<person>
	<Section>E</Section>
	<name>Karan</name>
</person>

Choice

Choice indicator means one of the child elements will come in XML. Consider the following XSD

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="person">
		<complexType>
			<choice>
				<element name="Section" type="string"/>
				<element name="name" type="string"/>
			</choice>
		</complexType>
	</element>
</schema>

So the XML which is validating against the XSD should contain either ‘name’ or ‘Section’ element. So for this XSD both XMLs are fine.

<person>
	<name>Karan</name>
</person>

<person>
	<Section>E</Section>
</person>

Sequence

As discussed in the ‘Introduction to XSD’ tutorial, sequence means child elements will occur in a particular order as mentioned inside the sequence indicator.

Minoccurs And Maxoccurs

minOccurs specifies the minimum number of times an element can occur and maxOccurs specifies the maximum number of times an element can occur. Consider the following XSD

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="subject">
		<complexType>
			<sequence>
				<element name="name" type="string"/>
				<element name="books" type="string" minOccurs="1" maxOccurs="3"/>
			</sequence>
		</complexType>
	</element>
</schema>

Here minOccurs and maxOccurs are specified in ‘books’ element. It means ‘books’ should occur minimum of 1 time and maximum of 3 times. So following XMLs are fine

<subject>
	<name>xml</name>
	<books>Book 1</books>
</subject>

<subject>
	<name>xml</name>
	<books>Book 1</books>
	<books>Book 2</books>
</subject>

<subject>
	<name>xml</name>
	<books>Book 1</books>
	<books>Book 2</books>
	<books>Book 3</books>
</subject>

There are couple of points which is worth to explain here

If you use minOccurs then it is required to use maxOccurs as well
If you have not specified minOccurs then default value 1 is assigned to it.

Element Group

Element group indicator allows you to define a set of related elements.

Syntax

<x:group name=“group_name">
</x:group>

Here ‘x’ is the object of namespace. Consider an example of following XSD.

<x:schema
	xmlns:x="http://www.w3.org/2001/XMLSchema">
	<x:group name="personInfo">
		<x:sequence>
			<x:element name="name" type="x:string"/>
			<x:element name="age" type="x:int"/>
			<x:element name="Gender" type="x:string"/>
		</x:sequence>
	</x:group>
	<x:element name="person" type="personType"/>
	<x:complexType name="personType">
		<x:sequence>
			<x:group ref="personInfo"/>
			<x:element name="Address" type="x:string"/>
		</x:sequence>
	</x:complexType>
</x:schema>

In the XSD above we have put all the elements that are related (belong the person) in one group. So for the following XSD this XML will be fine

<person>
	<name>Karan</name>
	<age>33</age>
	<Gender>M</Gender>
	<Address>Gurgaon</Address>
</person>

Attribute Group

Attribute group indicators allows you to define a set of attributes.

Syntax

<x:attributeGroup  name=“attr_group_name">
</x:attributeGroup>

Consider the following XSD

<x:schema
	xmlns:x="http://www.w3.org/2001/XMLSchema">
	<x:attributeGroup name="personAttributes">
		<x:attribute name="name" type="x:string"/>
		<x:attribute name="age" type="x:integer"/>
	</x:attributeGroup>
	<x:element name="person">
		<x:complexType>
			<x:attributeGroup ref="personAttributes"/>
		</x:complexType>
	</x:element>
</x:schema>

Here we have grouped attributes related to the person together. So the XML could be

<person name="Karan" age="33">
</person>

Posted By -	Karan Gupta

Posted On -	Friday, January 9, 2015

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