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Restrictions In XSD

In the last tutorial I explained about how to create a basic XSD document and how to validate a XML document against a XSD using SQL server. In this tutorial I will move a step ahead and explain about restrictions in XSD.

Restriction literally means – ‘the limitation or control of someone or something’. In XSD as well restrictions does the same thing.

Restriction is for defining acceptable values for xml elements and attributes. In this tutorial we will talk about 5 types of restrictions

Restrictions on Values
Restriction on set of values
Restriction on series of values
Restrictions on whitespace characters
Restrictions on length

Restrictions On Values

In this type of restriction we specify minimum and maximum allowable values.

Syntax (minimum value)

<element name=“name_of_element">
	<simpleType>
		<restriction base=“integer">
			<minInclusive value = “min_val" />
		</restriction>
	</simpleType>
</element>

Syntax (maximum value)

<element name=“name_of_element">
	<simpleType>
		<restriction base=“integer">
			<maxInclusive value = “max_val" />
		</restriction>
	</simpleType>
</element>

You can specify both min value and max value for an element. Consider an example of a XML which contains information about the person. Our requirement is to set the minimum and maximum value of age to 18 and 33.

<person>
	<name>Karan</name>
	<age>33</age>
	<maritalStatus>Single</maritalStatus>
</person>

XSD for the above XML would be

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="person">
		<complexType>
			<sequence>
				<element name="name" type="string"/>
				<element name="age">
					<simpleType>
						<restriction base="integer">
							<minInclusive  value = "18" />
							<maxInclusive  value = "33" />
						</restriction>
					</simpleType>
				</element>
				<element name="maritalStatus" type="string" />
			</sequence>
		</complexType>
	</element>
</schema>

Restriction On Set Of Values

In this restriction, allowable values of XML element are limited to a set of values.

Syntax

<element name=“element_value">
	<simpleType>
		<restriction base=“string">
			<enumeration value=“Val 1"/>
			<enumeration value=" Val 2"/>
			<enumeration value=“Val 3"/>
		</restriction>
	</simpleType>
</element>

Consider an example of a XML data which contains the information about a person. The information contains name, age and marital status. Our requirement is that the value in marital status should be limited to ‘Married’, ‘Divorce’ and ‘Single’

<person>
	<name>Karan</name>
	<age>33</age>
	<maritalStatus>Single</maritalStatus>
</person>

XSD for the above XML would be

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="person">
		<complexType>
			<sequence>
				<element name="name" type="string"/>
				<element name="age" type="integer"/>
				<element name="maritalStatus">
					<simpleType>
						<restriction base="string">
							<enumeration value="Married"/>
							<enumeration value="Single"/>
							<enumeration value="Divorced"/>
						</restriction>
					</simpleType>
				</element>
			</sequence>
		</complexType>
	</element>
</schema>

Restriction On Series Of Values

In this restriction we can define a regular expression in XSD and control the value of XML element accordingly.

Syntax

<element name=“element_value">
	<simpleType>
		<restriction base=“string">
			<pattern value=“pattern”/>
		</restriction>
	</simpleType>
</element>

Consider an example of a XML data in which contains the information about the student. XML contains following information – ‘Name’ and ‘Section’. Our requirement is that the section element should only contain the value from A to E.

<student>
	<name>Karan</name>
	<Section>E</Section>
</student>

XSD for the above XML would be

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="student">
		<complexType>
			<sequence>
				<element name="name" type="string"/>
				<element name="Section">
					<simpleType>
						<restriction base="string">
							<pattern  value = "[A-E]" />
						</restriction>
					</simpleType>
				</element>
			</sequence>
		</complexType>
	</element>
</schema>

Restrictions On Whitespace Characters

This restriction defines the way white spaces are handled in XML. There are 2 ways of handling white space

preserve – preserve option ensures that XML processor will not remove any white space.
collapse – collapse option ensures that XML processor removes white spaces

Syntax for preserve

<element name=“element_value">
	<simpleType>
		<restriction base=“string">
			<whiteSpace value=“preserve”/>
		</restriction>
	</simpleType>
</element>

Syntax for collapse

<element name=“element_value">
	<simpleType>
		<restriction base=“string">
			<whiteSpace value=“collapse”/>
		</restriction>
	</simpleType>
</element>

Consider the following XML

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

If you use preserve option then whitespaces are preserved in section element else whitespaces will be removed.

Restrictions On Length

This restriction limits the length of a value of a XML element.

Syntax

<element name=“element_value">
	<simpleType>
		<restriction base=“string">
			<length value=“max_length”/>
		</restriction>
	</simpleType>
</element>

Consider an example of a XML which contains information about a student. XML contains following elements – Name and Section. Now our requirement is to restrict the length of section to one.

<student>
	<name>Karan</name>
	<Section>E</Section>
</student>

So the XSD for the above XML would be

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="student">
		<complexType>
			<sequence>
				<element name="name" type="string"/>
				<element name="Section">
					<simpleType>
						<restriction base="string">
							<length value="1" />
						</restriction>
					</simpleType>
				</element>
			</sequence>
		</complexType>
	</element>
</schema>

I hope you like this tutorial. Please let me know your feedback. Thanks a lot for reading this tutorial.

Posted By -	Karan Gupta

Posted On -	Wednesday, January 7, 2015

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