Differentiate between validating and non validating xml parser
Even though a DTD is not mandatory for an application to read and understand a XML document, many developers recommend writing DTDs for your XML applications.
The W3C XML Schema Working Group received many proposals contributed as notes: Nontypical of schema languages, Schematron (SCH) was first proposed in September 1999 by Rick Jelliffe of the Academia Sinica Computing Centre and defines validation rules using XPath expressions.
W3C XML Schema is a strongly typed schema language that eliminates any non-deterministic design from the described markup to insure that there is no ambiguity in the determination of the datatypes and that the validation can be made by a finite state machine.
A W3C XML Schema schema for our sample could be Its editors (James Clark and Murata Makoto) define RELAX NG as "the next generation schema language for XML: clean, simple and powerful".
One of the key strengths of XML, sometimes called "late binding," is the decoupling of the writer and the reader of an XML document: this gives the reader the ability to have its own interpretation and understanding of the document.
It is generally considered complex, partly because of the number of features, and partly because of the style of the recommendation which describes the validation process more than the modeling features.
This, together with the fact that its datatype system is weak and only applies to attributes, is one of the main motivations for the W3C to develop a new schema language.