What is java DTD?

Answer 1

A DTD is the original type of XML schema. XML Schemas are used to formally describes the contents of an XML document. An XML schema describes the shape of the XML document, defining the data, sub elements or attributes it can contain, along with the number of times given entities can occur. A document type definition (DTD) is a set of markup declarations that define a document type for an SGML-family markup language (SGML, XML, HTML). A Document Type Definition (DTD) defines the legal building blocks of an XML document. It defines the document structure with a list of legal elements and attributes.

Answer 2

One method of constraining and validating the content of XML files is the Document Type Definition. Although part of the XML specification, DTDs (and XML files that reference them) aren't quite as straight-forward to parse as the standalone </>-type syntax we've come to know and love. The two main methods of parsing DTDs are DOM (Document Object Model) and SAX (Simple API for XML). The difference is that the DOM builds the entire representation of the document in memory before parsing begins. But with SAX, as each item is seen as the document is parsed, an event is 'fired' into your program, and it is up to you to keep track of what you care about.