The <schema> element is the root element of every XML Schema.
The <schema> Element
The <schema> element is the root element of every XML Schema:
<?xml version="1.0"?>
<xs:schema>
...
...
</xs:schema>
The <schema> element may contain some attributes. A schema declaration often looks something like this:
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3ii.com"
xmlns="http://www.w3ii.com"
elementFormDefault="qualified">
...
...
</xs:schema>
The following fragment:
xmlns:xs="http://www.w3.org/2001/XMLSchema"
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:
This fragment:
targetNamespace="http://www.w3ii.com"
indicates that the elements defined by this schema (note, to, from, heading, body.) come from the "http://www.w3ii.com" namespace.
This fragment:
xmlns="http://www.w3ii.com"indicates that the default namespace is "http://www.w3ii.com".
This fragment:
elementFormDefault="qualified"indicates that any elements used by the XML instance document which were declared in this schema must be namespace qualified.
Referencing a Schema in an XML Document
This XML document has a reference to an XML Schema:
<?xml version="1.0"?>
<note xmlns="http://www.w3ii.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3ii.com note.xsd">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
The following fragment:
xmlns="http://www.w3ii.com"specifies the default namespace declaration. This declaration tells the schema-validator that all the elements used in this XML document are declared in the "http://www.w3ii.com" namespace.
Once you have the XML Schema Instance namespace available:
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
you can use the schemaLocation attribute. This attribute has two values, separated by a space. The first value is the namespace to use. The second value is the location of the XML schema to use for that namespace:
xsi:schemaLocation="http://www.w3ii.com note.xsd"