Friday, 7 November 2014

First XML Schema


Before writing XML schema, let’s understand basic concepts.

1. Simple Type Element
An XML element with only text data (No attributes, no child elements) is called Simple type element.

Example
<salary>70000</salary>
<name>Krishna</name>

Above two are simple type elements.

<designation experience=”4Yrs”>Software Developer</designation>
Above element is not simple type element, since it has attribute “experience”.

2. Complex Element
Element other than simple type is considered to be complex type element.

Example
<employee>
  Employee Details
  <name>Krishna</name>
  <salary currency="rupees">80000</salary>
</employee>

In the above example, elements employee and salary are complex type elements, whereas name and currency are simple elements.

<?xml version="1.0" encoding="UTF-8"?>
   
<employees>

    <employee>
        <id>1</id>
        <name>
            <firstname>Hari</firstname>
            <middlename>Krishna</middlename>
            <lastname>Gurram</lastname>
            <age>25</age>
            <salary>80000</salary>
            <married>single</married>
        </name>

        <project>
            <department>aero</department>
            <pjtname>Flight Controls</pjtname>
            <from>2011-09-16</from>
            <to>2013-01-22</to>
        </project>

        <project>
            <department>banking</department>
            <pjtname>Online Transaction Processing System</pjtname>
            <from>2013-01-23</from>
            <to>2014-10-06</to>
        </project>

        <project>
            <department>mobile</department>
            <pjtname>Daily News Application</pjtname>
            <from>2014-10-07</from>
            <to>2015-05-06</to>
        </project>
    </employee>
</employees>


Consider the above example,

Elements in employee.xml are
employees, employee, id, name, firstname, middlename, lastname, age, salary, married, project, department, pjtname, from, to.

Let’s differentiate simple and complex elements in employee.xml

Simple elements in employee.xml are
id, firstname, middlename, lastname, age,salary, married, department, pjtname, from, to are simple elements, since they contains only text data (No attributes and child elements).

Complex elements in employee.xml are
employees, employee, name, project are complex elements.

it is time to write XML Schema file.

Step1: Create employee.xsd file. ‘xsd’ stands for XML Schema Definition and it is a w3c recommendation to specify  how to formally describe the elements in an Extensible Markup Language(XML).

Step 2: Create schema element in employee.xsd file.

<?xml version="1.0" encoding="UTF-8"?>

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

</xs:schema>
As you observe, xsd document itself XML document, so above statement contains xml declaration on top.

‘xmlns:xs="http://www.w3.org/2001/XMLSchema" '

Above snippet indicates that the elements and data types used in the schema come from the "http://www.w3.org/2001/XMLSchema" namespace. It also specifies that the elements and data types that come from the "http://www.w3.org/2001/XMLSchema" namespace should be prefixed with xs.

Step 3: Define simple elements.

Syntax to define simple element
<xs:element name="nameOf TheElement " type="datatype" />

XML schema comes with lot of built in type like string, decimal, integer, boolean, date, time etc., we will discuss about data types later.

Definitions for simple elements looks like below.
        <!-- Schema for simple elements -->
        <xs:element name="id" type="xs:integer" />
  <xs:element name="firstname" type="xs:string" />
  <xs:element name="middlename" type="xs:string" />
  <xs:element name="lastname" type="xs:string" />
  <xs:element name="age" type="xs:integer" />
        <xs:element name="salary" type="xs:decimal" />
        <xs:element name="married" type="xs:string" />
        <xs:element name="department" type="xs:string" />
        <xs:element name="pjtname" type="xs:string" />
  <xs:element name="from" type="xs:date" />
  <xs:element name="to " type="xs:date" />

xs:string, xs:integer, xs:date are predefined data types of XML Schema.

Step 3: Define complex elements.
We define schema for below snippet.

<project>
  <department>aero</department>
  <pjtname>Flight Controls</pjtname>
  <from>2011-09-16</from>
  <to>2013-01-22</to>
</project>


Schema for the element project looks like below.

        <!-- Schema for element project -->
  <xs:element name="project">
    <xs:complexType>
      <xs:sequence>
                            <xs:element ref="department" />
                            <xs:element ref="pjtname" />
                            <xs:element ref="from" />
                            <xs:element ref="to" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>

<xs:complexType>: Defines a complex type, which determines the set of attributes and the content of an element.
<xs:sequence> : Specifies elements in the group to appear in the specified sequence within the containing element.
<xs:element ref="pjtname"/>: ‘ref’ attribute specifies the name of an element declared in this schema.

Complete employees.xsd file looks like below.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <!-- Schema for simple elements -->
        <xs:element name="id" type="xs:integer" />
  <xs:element name="firstname" type="xs:string" />
  <xs:element name="middlename" type="xs:string" />
  <xs:element name="lastname" type="xs:string" />
  <xs:element name="age" type="xs:integer" />
        <xs:element name="salary" type="xs:decimal" />
        <xs:element name="married" type="xs:string" />
        <xs:element name="department" type="xs:string" />
        <xs:element name="pjtname" type="xs:string" />
  <xs:element name="from" type="xs:date" />
  <xs:element name="to " type="xs:date" />
        
  <!-- Schema for element name -->
  <xs:element name="name">
    <xs:complexType>
      <xs:sequence>
                            <xs:element ref="firstname" />
                            <xs:element ref="middlename" />
                            <xs:element ref="lastname" />
                            <xs:element ref="age" />
                            <xs:element ref="salary" />
                            <xs:element ref="married" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>

         <!-- Schema for element project -->
  <xs:element name="project">
    <xs:complexType>
      <xs:sequence>
                            <xs:element ref="department" />
                            <xs:element ref="pjtname" />
                            <xs:element ref="from" />
                            <xs:element ref="to" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>

         <!-- Schema for element employee -->
  <xs:element name="employee">
    <xs:complexType>
      <xs:sequence>
                            <xs:element ref="id" />
                            <xs:element ref="name" />
                            <xs:element ref="project" maxOccurs="unbounded" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>

          <!-- Schema for element employees -->
  <xs:element name="employees">
    <xs:complexType>
      <xs:sequence>
                            <xs:element ref="employee" maxOccurs="unbounded" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
  
</xs:schema>

Link employees.xsd file to employees.xml file
<employees xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="employees.xsd">

Update employees tag like above in employees.xml file.

employee.xml
<?xml version="1.0" encoding="UTF-8"?>
   
<employees xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="employees.xsd">

    <employee>
        <id>1</id>
        <name>
            <firstname>Hari</firstname>
            <middlename>Krishna</middlename>
            <lastname>Gurram</lastname>
            <age>25</age>
            <salary>80000</salary>
            <married>single</married>
        </name>

        <project>
            <department>aero</department>
            <pjtname>Flight Controls</pjtname>
            <from>2011-09-16</from>
            <to>2013-01-22</to>
        </project>

        <project>
            <department>banking</department>
            <pjtname>Online Transaction Processing System</pjtname>
            <from>2013-01-23</from>
            <to>2014-10-06</to>
        </project>

        <project>
            <department>mobile</department>
            <pjtname>Daily News Application</pjtname>
            <from>2014-10-07</from>
            <to>2015-05-06</to>
        </project>
    </employee>
</employees>

You can validate employees.xml file now.

You can validate the document online also. Goto below site and validate your data.


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