The Parser and DOM

1
The Parser and DOM
2
Introduction
3
XML Parser

• XML Parser
• A software component sitting between the
  application and the XML files
• Read and interpret the XML syntax
• Validating and Non-validating parsers

4
The Parser and the Application
5
The Architecture of an XML Program

• Interface between Parser and Application
• Object-Based Interface
• Event-Based Interface

6
Object-Based Interface

• Parser explicitly builds a tree of objects
  containing all the element in an XML document
• Example prices.xml

7
Event-Based Interface

• The parser reads an XML file and generates events
  as it finds elements, attributes, or text in the
  file

8
Object-based VS Event-based

• Object-based interface
• For applications that manipulate XML documents
  such as browsers, XSL processors
• Event-based interface
• Applications that maintain their own data
  structure in a non-XML format
• Import XML documents in a databases
• More efficient

9
Standards

• Object-based interface
• DOM Document Object Model
• http//www.w3.org/DOM/
• Event-based interface
• SAX Simple API for XML
• http//www.megginson.com/SAX/

10
DOM

• Originally developed for browsers
• DOM Level
• Level 1 well-formed documents
• Level 2 valid documents
• under development
• DOM defines classes of objects to represent every
  element in an XML file.

11
The Hierarchy in DOM
12
Getting Started with DOM
13
Client-Side Scripting with XML DOM
Loading XML Doc.
XML
IE 5.0
HTML
XML DOM
XML Parser(msxml)
JS Code

• DHTML
• HTML

XML Tags Data
14
Example

• Essential files
• prices.xml
• convert.html
• conversion.js

15
XML Data Island
history
window
forms
navigator
document
images
XML data island
etc
XML Document
16
DOM Node

• The core object in DOM tree is Node
• Generic objects in DOM
• Most DOM objects are derived from Node
• searchPrice() tests if the current node is an
  element

• Node Properties
• nodeType
• parentNode
• childNodes
• firstChild
• lastChild
• previousSibling
• nextSibling
• attributes
• nodeName
• nodeValue

17
nodeType Code

• Element 1
• Attribute 2
• Text 3
• CDATA Section 4
• Entity reference 5
• Entity 6
• Processing instruction7

• Comment 8
• Document 9
• Document Type 10
• Document fragment 11
• Notation 12

18
Document Object

• The topmost element in a DOM tree is Document
• Inherits from Node
• Two more properties
• documentElement XML top-element
• doctype Document type (DOM Level 2)
• Document is similar to the root in XSL path
• To return a tree, the parser returns a Document
  Object
• xmldocument returned in parse() function is a
  Document object

19
Walking the Element Tree

• Recursively traverse the DOM tree
• Do any node-specific processing, such as
  outputing data
• Visit all its children
• searchPrice()
• childNodes child list
• length
• item(i)

20
Element Object

• Element
• Descendant of node to represent XML elements
• Property and method
• tagName for an elements tag name
• getElementsByTagName()
• normalize()

21
Text Object

• textNode.data to get the content of a text object
• ltpgtThe element can contain text and other
  elements such as images ltimg srclogo.gif /gt or
  others. lt/pgt
• ltpgt contains two text objects and one element
  object (ltimggt)
• To retrieve the text of an element, it is safer
  to iterate over the elements children

22
Managing the State

• It is common to collect information from several
  elements or to process elements only if they are
  children of other elements.
• Must maintain state information
• Remember where its coming from or what children
  it is expecting

• Example
• convert2.html
• conversion2.js
• walkNode()
• walkProduct()

23
Attributes (I)

• Example convert3.html
• walkRate() Manipulating attributes
• Element objects have an attributes property
• The attributes property is a NamedNodeMap object

• NamedNodeMap
• A list of nodes with a named attached to them
• length and item(I)
• getNamedItem()
• setNamedItem()
• removeNamedItem()

24
Attributes (II)

• Attr objects
• Represent the attributes
• A Node descendant
• Properties
• name name of the attribute
• value value of the attribute
• specified true if the attribute was given a
  value in the document false if the attribute has
  taken a default value from the DTD

25
DOM in Other Languages

• DOM and Java
• IBM XML for Java
• Xerces-J (Apache)
• XML Parser for C
• Xerces-C (Apache)
• XML Parser for Perl
• XML Parser Module
• MSXML Technology Preview SDK