Document%20Object%20Model%20(DOM)%20MV4920%20

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Document Object Model(DOM)MV4920 XML24
September 2001

• Simon R. GoergerMAJ, US Army
• srgoerge_at_cs.nps.navy.mil

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Outline

• Goal
• DOM Description
• DOM Basics
• Tree
• Levels
• DOM Examples
• DOM Demo
• DOM Resources
• Summary

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Goal

• The goal of the DOM group is to define a
  programmatic interface for XML and HTML.

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What is a DOM?

• Document Object Model (DOM)
• A programming interface for XML documents
• It defines the way an XML document can be
  accessed and manipulated.
• A platform- and language-neutral interface that
  will allow programs and scripts to dynamically
  access and update the content, structure and
  style of documents. The document can be further
  processed and the results of that processing can
  be incorporated back into the presented page.

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What a DOM is NOT

• Although the Document Object Model was strongly
  influenced by "Dynamic HTML", in Level 1, it does
  not implement all of "Dynamic HTML". In
  particular, events have not yet been defined.
  Level 1 is designed to lay a firm foundation for
  this kind of functionality by providing a robust,
  flexible model of the document itself.
• The Document Object Model is not a binary
  specification. DOM programs written in the same
  language will be source code compatible across
  platforms, but the DOM does not define any form
  of binary interoperability.
• The Document Object Model is not a way of
  persisting objects to XML or HTML. Instead of
  specifying how objects may be represented in XML,
  the DOM specifies how XML and HTML documents are
  represented as objects, so that they may be used
  in object oriented programs.

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What a DOM is NOT

• The Document Object Model is not a set of data
  structures, it is an object model that specifies
  interfaces. Although this document contains
  diagrams showing parent/child relationships,
  these are logical relationships defined by the
  programming interfaces, not representations of
  any particular internal data structures.
• The Document Object Model does not define "the
  true inner semantics" of XML or HTML. The
  semantics of those languages are defined by W3C
  Recommendations for these languages. The DOM is a
  programming model designed to respect these
  semantics. The DOM does not have any
  ramifications for the way you write XML and HTML
  documents any document that can be written in
  these languages can be represented in the DOM.

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What a DOM is NOT

• The Document Object Model, despite its name, is
  not a competitor to the Component Object Model
  (COM). COM, like CORBA, is a language independent
  way to specify interfaces and objects the DOM is
  a set of interfaces and objects designed for
  managing HTML and XML documents. The DOM may be
  implemented using language-independent systems
  like COM or CORBA it may also be implemented
  using language-specific bindings like the Java or
  ECMAScript bindings specified in this document.

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What can a DOM do?

• With the XML DOM, a programmer can create an XML
  document, navigate its structure, and add,
  modify, or delete its elements.

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DOM Tree

• The DOM represents a tree view of the XML
  document. The documentElement is the top-level of
  the tree. This element has one or many childNodes
  that represent the branches of the tree.

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Why the Document Object Model?

• "Dynamic HTML" is a term used by some vendors to
  describe the combination of HTML, style sheets
  and scripts that allows documents to be animated.
  The W3C has received several submissions from
  members companies on the way in which the object
  model of HTML documents should be exposed to
  scripts. These submissions do not propose any new
  HTML tags or style sheet technology. The W3C DOM
  WG is working hard to make sure interoperable and
  scripting-language neutral solutions are agreed
  upon.

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DOM Level (Architecture)

• The DOM is separated into three parts Core,
  HTML, and XML. The Core DOM provides a low-level
  set of objects that can represent any structured
  document. While by itself this interface is
  capable of representing any HTML or XML document,
  the core interface is a compact and minimal
  design for manipulating the document's contents.
  Depending upon the DOM's usage, the core DOM
  interface may not be convenient or appropriate
  for all users. The HTML and XML specifications
  provide additional, higher-level interfaces that
  are used with the core specification to provide a
  more convenient view into the document. These
  specifications consist of objects and methods
  that provide easier and more direct access into
  the specific types of documents.

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DOM Level (Architecture)

• The DOM Architecture is divided in four module
  levels. Each module addresses or specializes an
  existing module for a particular domain. Domains
  covered by the current DOM API are XML, HTML,
  CSS, and events.
• DOM Level 0
• Functionality equivalent to that exposed in
  Netscape Navigator 3.0 and Microsoft Internet
  Explorer 3.0 is referred to as "Level 0". There
  is no W3C specification for this Level.

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DOM Level 1 (Architecture)

• DOM Level 1
• The first Level of the DOM specifications (DOM
  Level 1) was completed in October 1998. Level 1
  provides support for XML 1.0 and HTML

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DOM Level 2 (Architecture)

• DOM Level 2
• The second Level of the DOM specifications (DOM
  Level 2) was completed in November 2000. Level 2
  extends Level 1 with support for XML 1.0 with
  namespaces and adds supports for Cascading Style
  Sheets (CSS), events (user interface events and
  tree manipulation events), and enhances tree
  manipulations (tree ranges and traversal
  mechanisms).

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DOM Level 3 (Architecture)

• DOM Level 3
• The third Level of the DOM specifications, DOM
  Level 3, is under development. Level 3 will
  extend Level 2 by finishing support for XML 1.0
  with namespaces (alignment with the XML Infoset
  and support for XML Base) and will extend the
  user interface events (keyboard). It will also
  add abstract schemas support (for DTDs, XML
  Schema, ...), the ability to load and save a
  document or an abstract schema, explore further
  mixed markup vocabularies and the implications on
  the DOM API ("Embedded DOM"), and will support
  XPath.

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DOM Level Future

• Further Levels. These may specify some interface
  with the possibly underlying window system,
  including some ways to prompt the user. They may
  also contain a query language interface, and
  address multithreading and synchronization,
  security, and repository.

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Example

• Simple example of DOM usage (input)
• DocumentBuilderFactory documentBuilderFactory
• DocumentBuilderFactory.newInstance ()
• documentBuilderFactory.setNamespaceAware (true)
• documentBuilderFactory.setValidating (true)
• DocumentBuilder documentBuilder
• documentBuilderFactory.newDocumentBuilder ()
• Document document documentBuilder.newDocument
  ()
• try
• document documentBuilder.parse (fileName)
• // end try
• catch (Exception badParse)

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Example

• Simple example of DOM usage (output)
• Writer writer new OutputStreamWriter(file)
• switch (node.getNodeType())
• case Node.CDATA_SECTION_NODE
• writer.write ("lt!CDATA"
  node.getNodeValue()
• "gt\n")
• break
• // end switch

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Demo

• Problem read incomplete XML document, merge
  with DTD to identify missing attributes, read
  directory structure to locate information to
  update default values, and output new XML
  document with updates.
• Demo XMLtoDOMtoXML.bat

DOM
Updated Dom
Updated XML Document
Directories (access with Java code)
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Resources

• Some resources related to the DOM are to be found
  at
• Robin Cover's DOM pages
• http//www.oasis-open.org/cover/dom.htmlW3CDocs
  
• the Open Directory Project W3C DOM pages
  http//dmoz.org/Computers/Programming/Internet/W
  3C_DOM/
• Some related DOM-based APIs are being developed
  as well, for example in the specifications for
• Mathematical Markup Language http//www.w3.org/T
  R/MathML2/
• Scalable Vector Graphics http//www.w3.org/TR/SV
  G/
• Synchronized Multimedia Integration Language
  http//www.w3.org/TR/smil-boston-dom/
• NOTE Placing the following .jar files from JAXP
  in your jdk../jre/lib/ext directory, maybe
  required for use of the DOM crimson.jar,
  jaxp.jar, and xalan.jar

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Summary

• DOM is a programming interface for XML documents
  that defines the way an XML document can be
  accessed and manipulated.