Document Type Definition (DTD) describes a model or set of rules for an XML document. XML Schema Definition (XSD) also describes the structure of an XML document but XSDs are much more powerful.
The disadvantage with the Document Type Definition is it doesn’t support data types beyond the basic 10 primitive types. It cannot properly define the type of data contained by the tag.
An Xml Schema provides an Object Oriented approach to defining the format of an xml document. The Xml schema support most basic programming types like integer, byte, string, float etc., We can also define complex types of our own which can be used to define a xml document.
Xml Schemas are always preferred over DTDs as a document can be more precisely defined using the XML Schemas because of its rich support for data representation.