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Introduction To XSD

From the last couple of weeks I was studying XSD. I found it really interesting, so I decided to share the knowledge with you.

Before we start knowing about XSD, you should know basics about XML. Although I will explain some of the basics which I feel are required for the understanding of XSD.

What Is XSD?

XSD stands for XML Schema Definition. In computer science schema means defining the structure of a document. Similarly XSD defines the structure of a XML document (or data).

Defining a XML structure means put validation on the way elements and attributes are defined in XML. Apart from this XSD also controls the data type assigned to elements and attributes of XML element.

Back To Basics - Types Of XML Element

XML supports 2 types of elements

Simple element – Simple elements are those XML elements which don’t have child elements or attributes.

<element_name>text</element_name>

Complex element – Complex elements are those XML elements which contain child elements or attributes.

<element_name attribute1=”attribute_value”>
.. Child nodes or text
</element_name>

Validate XML Against XSD

There are various online and offline tools for validating XML against XSD. But in this tutorial (and in all the subsequent tutorials) I will use SQL server for the same.

Follow these steps

Open query analyzer
Write following code

-- Create a XML schema collection
Create XML schema collection TestSchemaCollection As '
XSD ' -- XSD against which XML will be validated 
GO

--  Create a table with a single column of data type XML
Create table TestTable
(
	MyXMLSample XML (TestSchemaCollection) 
)

-- Insert a XML into the table
-- Insertion will be success if XML is valid
-- else insert statement will throw an error.
Insert into TestTable values('XML')

-- Finally drop a table and XML schema collection
drop table TestTable
drop xml schema collection TestSchemaCollection

Comments are written against each step.

Run the query.

As mentioned in the comments if the XML is invalid then values will not be inserted into the table.

Schema Element In XSD

Each XSD document starts with a schema element. Inside the schema we define an attribute for adding namespace.

Syntax

<schema xmlns="http://www.w3.org/2001/XMLSchema">
..
</schema>

Simple XML Element In XSD

For simple element XSD can be defined as

<element name="element_name" type="data_type" />

Here ‘element’ is the keyword.

Complex XML Element In XSD

For complex element XSD can be defined as

Complex types are defined as

<element name="name_of_complex_element">
	<complexType>
		<group_indicator>
        .. 
        List of simple types of xml elements
     
		</ group_indicator>
	</complexType>
</element>

You will come to know about group indicators in subsequent tutorials.

XML Attributes In XSD

For attributes XSD can be defined as

<attribute name="" type=""/>

Data Types Supported By XSD

XSD supports following data type

string
decimal
integer
boolean
date
time

Examples

In this section we will work on some sample XML data and create the XSD accordingly

Consider the following XML

<Blogs>
	<blog category="Technical">
		<title>Code Project</title>
		<URL>CodeProject.com</URL>
	</blog>
</Blogs>

In the XML above ‘Blogs’ and ‘blog’ are complex elements whereas ‘title’ and ‘URL’ are simple elements. XSD for the above XML would be

<schema
	xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="Blogs">
		<complexType>
			<sequence>
				<element name="blog">
					<complexType>
						<sequence>
							<element name="title" type="string" />
							<element name="URL" type="string" />
						</sequence>
						<attribute name="category" type="string"/>
					</complexType>
				</element>
			</sequence>
		</complexType>
	</element>
</schema>

Here ‘sequence’ is an indicator (more indicators will be explained in subsequent tutorials). Sequence means all child elements inside the sequence will be in the same order in XML as in XSD. For example in the example above if ‘URL’ comes before ‘title’ in XML then XML validation against XSD will fail. You can test it using the SQL query which I have put above.

Posted By -	Karan Gupta

Posted On -	Sunday, January 4, 2015

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