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DTD and XML Schema structures: conversion methods for J2EE and XML developers.

Article Excerpt
This article compares Document Type Definition (DTD) and XML Schema elements. Java 2 Enterprise Edition (J2EE) developers use DTDs and schemas in I2EE/XML applications. When a DTD for an XML document is provided and validation with an XML Schema is required, the DTD-to-XML Schema conversion creates an XML Schema document corresponding to the DTD document.

Overview

A DTD defines the structure of an XML document and defines a document's element types, subelement types, and the order and number of each element type. It also declares the attributes, entities, notations, processing instructions, and comments. An XML Schema is an XML-based representation of the structure of a XML document. Among the advantages of XML Schema is support for data types and namespaces. XML Schema, being XML based, is an extensible, complex representation of an XML document structure.

In this tutorial the different DTD declarations and their equivalent declarations in an XML Schema, and the equivalent of the XML document DOCTYPE declaration, are discussed, including:

* DOCTYPE

* Comment

* Processing instructions

* Element

* Attribute

* Entity

* Notation

DOCTYPE Declaration

The DOCTYPE declaration in an XML document refers to a public URI and the system URI of an external DTD. If the XML document is validated, the document elements and attributes are validated with the element and attribute definitions specified in the DOCTYPE DTD. A DTD specified with a system and public identifiers is an external subset DTD. A DTD may also be specified as an internal subset. An internal subset DTD is specified in the DOCTYPE declaration, which may consist of a combination of internal and external DTDs.

The DOCTYPE declaration in an XML document is specified with the declaration.

* !DOCTYPE root element ((SYSTEM "system_uri") | (PUBLiC "public_uri" "system_uri" ) >

The system URI of a schema document is specified in an XML document with the xsi:schemaLocation and xsi:noNamespaceSchemaLocation attributes in the root element. The xsi:SchemaLocation...