XML

XML rules

• An XML document must be contained in a single element. - Named Root Element
• only comments can be out side the root element.
• XML elements cant overlap
• End tags are mandatory
• Elements are case sensitive
• XML attributes must have values given within quotes(single or double)
• <ol compact="yes">
• <!-- comments -->
• Processing instructions ? 
• Namespaces: to differentiate element tags which have the same name.
• Define namespace prefix: xmlns:addr="http://www.xyz.com/addresses/"
• Use prefix with xml elements: <books:title>
• Namespace definition must be a unique string

Defining Document Content

Document Type Definition: DTD

Syntax:

• An Element with comma separated values means the tags must appear and they should be in that order.
• Optional elements: "?" at the end of their name
• One or more elements: "+"
• Zero or more elements: "*"
• Choices separated with: "|"
• Attributes are defined giving the accepted values and whether it is optional or required
• <!ATTLIST city state CDATA #REQUIRED>

XML Schema

Elements:

<xsd:element name="address">

  <xsd:complexType>

    <xsd:sequence>

      <xsd:element ref="name"/>

      <xsd:element ref="street"/>

      <xsd:element ref="city"/>

      <xsd:element ref="state"/>

      <xsd:element ref="postal-code"/>

    </xsd:sequence>

  </xsd:complexType>

</xsd:element>

Elements:

<xsd:element name="postal-code">

    <xsd:simpleType>

      <xsd:restriction base="xsd:string">

        <xsd:pattern value="[0-9]{5}(-[0-9]{4})?"/>

      </xsd:restriction>

    </xsd:simpleType>

  </xsd:element>

Reference: http://www.ibm.com/developerworks/xml/tutorials/xmlintro/xmlintro.html