The XML Validation (eXtensible Markup Language) checks a document in XML language if it is well formed and it is adjusted to a defined structure. A well formed document follows the basic rules of XML established for the design of documents. Moreover a valid document respects the rules dictated by a DTD or XML schema. In addition extended tools are available such as OASIS CAM standard specification that provide contextual validation of content and structure that is more flexible than basic schema validations. The Extensible Markup Language (XML) is a general-purpose markup language. ... Document Type Definition (DTD), defined slightly differently within the XML and SGML specifications, is one of several SGML and XML schema languages, and is also the term used to describe a document or portion thereof that is authored in the DTD language. ... XML Schema, published as a W3C Recommendation in May 2001, is one of several XML schema languages. ...