XML with correct syntax is Well Formed XML.
XML validated against a DTD or a
Schema is a Valid XML.
Well Formed XML Documents
A "Well Formed" XML document has correct XML
syntax.
A "Well Formed" XML document is a document
that conforms to the XML syntax rules that were described in the previous
chapters:
- XML documents must have a root element
- XML elements must have a closing tag
- XML tags are case sensitive
- XML elements must be properly nested
- XML attribute values must always be quoted
<?xml version="1.0" encoding="ISO-8859-1"?> <E-mail> <To>Rohan</To> <From>Amit</From> <Subject>Surprise....</Subject> <Body>Be ready for a cruise...i will catch u tonight</Body> </E-mail> |
Valid XML Documents:
A "Valid" XML document is a "Well
Formed" XML document, which also conforms to the rules of a Document Type
Definition (DTD) or a XML Schema .
The following xml document is validated against a DTD ,
notice the highlighted text.
<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE e-mail SYSTEM "InternalE-mail.dtd"> <E-mail> <To>Rohan</To> <From>Amit</From> <Subject>Surprise....</Subject> <Body>Be ready for a cruise...i will catch u tonight</Body> </E-mail |
XML DTD
A DTD defines the legal elements of an XML document.
The purpose of a DTD is to define the legal building
blocks of an XML document. It defines the document structure with a list of
legal elements.
XML Schema
XML Schema is an XML based alternative to DTD .W3C supports an alternative to DTD called XML Schema.