Explain XML Schema

There are two types of XML  schemas.

®Internal  schema

®External schema

XML  schema is  an XML  based altanative  to DTD . An XML  schema describe the structure of an XML  document .XML schema  is also  referred  to as ‘ XML  schema definition’ (XSD ).

The purpose of XML schema is to  define the logical building blocks  of an XML  document  just Like  a  DTD.

XML schema:

® Defines  elements that  can appear  as in a document.

­® Define attributes that can appear in a document.

® Define which elements are child elements.

® Define the no.of child elements.

® Define whether an element is empty (or) can include text.

® Define data types for elements and attributes.

® Define data types for elements and attributes.

® Define default and fixed values for elements and attributes.

XML schema will be used in most web applications as a replacement for DTD’s.

1. XML schema’s are extensible to future additions.

2. XML schema’s are richer and more powerful than DTD

3. XML schema’s are written in XML.

4. XML schema’s support data type.

5. XML schema’s support name spaces

Eg:- < ? XML version = “ 1.0”?>

        <XS : schema xmins : xs = “http://www.W3.org/xml schema>

        <XS: element name ="note">

        <XS: complex type>

        <XS : sequence>

        <XS: element name = “to” type = “xs: string"/>

        <XS: element name = “from” type = “xs:string"/>

        </XS: sequence>

        </XS: complex type>

        </XS: element>

        </XS: schema>