07 - XML - DOM

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eXtensible Markup Language

Document Object Model 1.0

<?xml version=“1.0”><course startdate=“February 06, 2006”>

<title> eXtensible Markup Language </title>

<lecturer>Phan Vo Minh Thang</lecturer></course>

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<? xml version=“1.0”> <material> XML Lectures Notes <section id=“ 07 ”> Document Object Model </section> </material>

A Piece of XML

<seq id="my_seq" name="NUCLEAR RIBONUCLEOPROTEIN">

<dbxref>

<database>SWISS-PROT</database>

<unique_id>P09651</unique_id>

</dbxref>

<residues type="aa">

SKSESPKEPEQLRKLFIGGLSFETTDESLRSHFEQWGTLTDCVVMRDPNTKRS

RGFGFVTYATVEEVDAAMNARPHKVDGRVVEPKRAVSREDSQRPGAHLTVKKI

FVGGIKEDTEEHHLRDYFEQYGKIEVIEIMTDRGSGKKRGFAFVTFDDHDSVD

KIVIQKYHTVNGHNCEVRKALSKQEMASASSSQRGRSGSGNFGGGRGGGFGGN

DNFGRGGNFSGRGGFGGSRGGGGYGGSGDGYNGFGNDGGYGGGGPGYSGGSRG

YGSGGQGYGNQGSGYGGSGSYDSYNNGGGRGFGGGSGSNFGGGGSYNDFGNYN

NQSSNFGPMKGGNFGGRSSGPYGGGGQYFAKPRNQGGYGGSSSSSSYGSGRRF

</residues>

</seq>

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An XML DTD

<?xml version='1.0' encoding="US-ASCII"?>

<!DOCTYPE biosequence [

<!ELEMENT seq (dbxref*, residues?) >

<!ATTLIST seq id ID #REQUIRED

name CDATA #IMPLIED

length CDATA #IMPLIED >

<!ELEMENT residues (#PCDATA)>

<!ATTLIST residues type (dna | rna | aa) #REQUIRED>

]>

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Using a XML Parser

Three basic steps to using an XML parser

• Create a parser object

• Pass your XML document to the parser

• Process the results

Generally, writing out XML is outside scope of parsers(though some may implement proprietary mechanisms)

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Types of Parser

There are several different ways to categorise parsers:

• Validating versus non-validating parsers

• Parsers that support the Document Object Model (DOM)

• Parsers that support the Simple API for XML (SAX)

• Parsers written in a particular language (Java, C++, Perl, etc.)

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Non-validating Parsers

Speed and efficiency

• It takes a significant amount of effort for an XML parser to processa DTD and make sure that every element in an XML document

follows the rules of the DTD.

If only want to find tags and extract information - use non-validating

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Structure of XML

Logical Structure

• Elements

Physical Structure

• Entities

DocumentUnit

Sub-unit

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XML Hierarchy

Document

Unit

Sub-unit

Document

Unit

Sub-unit

N.B. All elements must be nested

XML can be described in a

tree hierarchy

Parent

Child

Sibling

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Parsing XML

Two established API's

• SAX (Simple API for XML)

Define handlers containing methods as XML parsed

• DOM (Document Object Model)

Defines a logical tree representing the parsed XML

Apps that don't require complex manipulation can useSAX

Apps that need structural manipulations of many XML

tokens should use DOM

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DOM

Document Object Model

Set of interfaces for an application thatreads an XML file into memory and stores itas a tree structure

The abstract API allows for constructing,accessing and manipulating the structureand content of XML and HTML documents

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Advantages of DOM

When you parse an XML document

with a DOM parser, you get back atree structure that contains all of the

elements of your document

The DOM provides a variety offunctions you can use to examine the

contents and structure of thedocument

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Why use the DOM?

Task of writing parsers is reduced to coding against anAPI for the document structure

Domain-specific frameworks will be written on top of DOM

Tag data in XML - Code against DOM interfaces to access

application data

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DOM versus SAX

If your document is very large andyou only need a few elements -use SAX

If you need to process manyelements and perform operationson XML - use DOM

If you need to access the XML

many times - use DOM

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DOM Standard

DOM 1.0 standard from www.w3.org Assumes an object-oriented approach

Composed of number of interfaces

• org.w3c.dom.*

Central class is 'Document' (DOM tree)

Standard does not include

• Tree walking

• Writing out XML format

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Creating a DOM Tree

A DOM implementation will have a method to pass a XMLfile to a factory object that will return a Document objectthat represents root element of whole document

After this, may use DOM standard interface to interact withXML structure

DOM Parser DOM TreeXML File

A

P

I

Application

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Creating a DOM Tree (2)

import org.w3c.dom.*; //DOM interfaces

import com.sun.xml.tree.*; //Using Sun classes

import org.xml.sax.*; //Need SAX classes

public class myClass {…

Document myDoc; //Document object

try {

//if 'true' -> validate myDoc =

XmlDocument.createXmlDocument("file:/doc.xml", true);

} catch (IOException err) {…}

catch (SAXException err) {…}

catch (DOMException err) {…}

//If no exceptions, should have a 'Document' object

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DOM Interfaces and Classes

DocumentFragment

Document

CharacterData

Text

Comment

CDATASection

Attr

Element

DocumentType

Notation

EntityEntityReference

ProcessingInstruction

Node NodeList

NamedNodeMap

DocumentType

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DOM Interfaces

The DOM defines several Java interfaces• Node The base data type of the DOM

• ElementRepresents element

• Attr Represents an attribute of an element• Text The content of an element or attribute

• Document Represents the entire XML

document. A Document object isoften referred to as a DOM tree

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Node Interface

Basic object of DOM (single node in tree)

Nodes describe

Node collections

• NodeList, NamedNodeMap, DocumentFragment

Several nodes extend the Node interface

Elements

Attributes

Text

Comments

CDATA sections

Entity declarations

Entity references

Notation declarations

Entire documents

Processing instructions

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Node Methods

Three categories of methods• Node characteristics

name, type, value

• Contextual location and access to relativesparents, siblings, children, ancestors, descendants

• Node modification

Edit, delete, re-arrange child nodes

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Node Methods (2)

short getNodeType();

String getNodeName();

String getNodeValue() throws DOMException;

void setNodeValue(String value) throws DOMException;

boolean hasChildNodes();

NamedNodeMap getAttributes();

Document getOwnerDocument();

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Node Types - getNodeType()

ELEMENT_NODE = 1

ATTRIBUTE_NODE = 2

TEXT_NODE = 3

CDATA_SECTION_NODE = 4

ENTITY_REFERENCE_NODE = 5

ENTITY_NODE = 6

PROCESSING_INSTRUCTION_NODE = 7

COMMENT_NODE = 8

DOCUMENT_NODE = 9

DOCUMENT_TYPE_NODE = 10

DOCUMENT_FRAGMENT_NODE = 11

NOTATION_NODE = 12

if (myNode.getNodeType() == Node.ELEMENT_NODE) {

//process node

…

}

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Node Names and Values

Every node has a name and possibly a value

Name is not a unique identifier (only location)

Type Interface Name Name Value

ATTRIBUTE_NODE Attr Attribute name Attribute value

DOCUMENT_NODE Document #document NULL

DOCUMENT_FRAGMENT_NODE DocumentFragment #document-fragment NULL

DOCUMENT_TYPE_NODE DocumentType DOCTYPE name NULL

CDATA_SECTION_NODE CDATASection #cdata-section CDATA content

COMMENT_NODE Comment Entity name Content string

ELEMENT_NODE Element Tag name NULL

ENTITY_NODE Entity Entity name NULL

ENTITY_REFERENCE_NODE EntityReference Entity name NULL

NOTATION_NODE Notation Notation name NULL

PROCESSING_INSTRUCTION_

NODE

ProcessingInstruction Target string Content string

TEXT_NODE Text #text Text string

Table as from “The XML Companion” - Neil Bradley

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Child Nodes

Most Nodes cannot have children, except

• Document, DocumentFragment, Element

Can check for presence of children

• if (myNode.hasChildNodes()) {

//process children of myNode

…

}

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Node Navigation

Every node has a specific location in tree

Node interface specifies methods to find surroundingnodes

• Node getFirstChild();

• Node getLastChild();

• Node get NextSibling();

• Node getPreviousSibling();

• Node getParent Node();

• NodeList getChild Nodes();

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Node Navigation (2)

getFirstChild()

getPreviousSibling()

getChildNodes()

getNextSibling()

getLastChild()

getParentNode()

Node parent = myNode.getParentNode();

if (myNode.hasChildren()) {

NodeList children = myNode.getChildNodes();

}

Figure as from “The XML Companion” - Neil Bradley

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Node Manipulation

Children of a node in a DOM tree can be manipulated -added, edited, deleted, moved, copied, etc.

Node removeChild(Node old) throws DOMException;

Node insertBefore(Node new, Node ref) throws DOMException;

Node appendChild(Node new) throws DOMException;

Node replaceChild(Node new, Node old) throws DOMException;

Node clone Node(boolean deep);

? l i “1 0” t i l XML L t N t ti id “07” D t Obj t M d l / ti / t i l

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Node Manipulation (2)

Ref

New

insertBefore

Old

New

replaceChild

cloneNode

Shallow 'false'

Deep 'true'

Figure as from “The XML Companion” - Neil Bradley

?xml version “1 0” material XML Lectures Notes section id “07” Document Object Model /section /material

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Document::Node Interface

Represents entire XML document (tree root)

Methods

//Information from DOCTYPE - See 'DocumentType'

DocumentType getDocumentType();

//Information about capabilities of DOM implementation

DOMImplementation getImplementation();

//Returns reference to root node element

Element getDocumentElement();

//Searches for all occurrences of 'tagName' in nodes

NodeList getElementsByName(String tagName);

<?xml version “1 0”> <material> XML Lectures Notes <section id “07”> Document Object Model </section> </material>

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<? xml version= 1.0 > <material> XML Lectures Notes <section id= 07 > Document Object Model </section> </material>

Document::Node Interface (2)

Factory methods for node creationElement createElement(String tagName) throws DOMException;

DocumentFragment createDocumentFragment();

Text createTextNode(String data);

Comment createComment(String data);

CDATASection createCDATASection(String data) throws

DOMException;ProcessingInstruction createProcessingInstruction(

String target, String data) throws DOMException;

Attr createAttribute(String name) throws DOMException;

EntityReference createEntityReference(String name)throws DOMException;

<?xml version=“1 0”> <material> XML Lectures Notes <section id=“07”> Document Object Model </section> </material>

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<? xml version= 1.0 > <material> XML Lectures Notes <section id= 07 > Document Object Model </section> </material>

DocumentType::Node Interface

Information about document encapsulated in DTDrepresentation

DOM 1.0 doesn’t allow editing of this node

//Returns name of document

String getName();

//Returns general entities declared in DTD

NamedNodeList getEntities();

//Returns notations declared in DTD

NamedNodeList getNotations();

<?xml version=“1 0”> <material> XML Lectures Notes <section id=“07”> Document Object Model </section> </material>

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<? xml version 1.0 > <material> XML Lectures Notes <section id 07 > Document Object Model </section> </material>

Element::Node Interface

Two categories of methods

• General element methods

• Attribute management methods

String getTagName();

NodeList getElementsByTagName();

void normalize();

String getAttribute(String name);void setAttribute(String name, String value)

throws DOMException;

void removeAttribute(String name)


Attr getAttributeNode(String name);void setAttributeNode(Attr new)


void removeAttributeNode(Attr old)



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e s o 0 ate a ectu es otes sect o d 0 ocu e t Object ode sect o ate a

Element::Node Interface (2)

Only Element objects have attributes but attributemethods of Element are simple

• Need name of attribute

• Cannot distinguish between default value specified in DTDand given in XML file

• Cannot determine attribute type [String]

Instead use getAttributes() method of Node

• Returns Attr objects in a NamedNodeMap


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j

Attr::Node Interface

Interface to objects holding attribute data

Entity ref's are children of attribute's

//Get name of attribute

String getName();

//Get value of attributeString getValue();

//Change value of attribute

void setValue(String value);

//if 'true' - attribute defined in element, else in DTD

boolean getSpecified();


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Attr::Node Interface (2)

Attributes not considered part of DOM• parentNode, previousSibling and nextSibling have

null value for Attr object

Create attribute objects using factory method ofDocument

//Create the empty Attribute node

Attr newAttr = myDoc.createAttribute("status");

//Set the value of the attributenewAttr.setValue("secret");

//Attach the attribute to an element

myElement.setAttributeNode(newAttr);


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CharacterData::Node Interface

Useful general methods for dealing with text

Not used directly

• sub-classed to Text and Comment Node types

String getData() throws DOMException;

void setData(String data) throws DOMException;

int getLength();

void appendData(String data) throws DOMException;

String substringData(int offset, int length)


void insertData(int offset, String data)


void deleteData(int offser, int length)


void replaceData(int offset, int length, String data)



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Text::Node Interface

Represents textual content of Element or Attr

• Usually children of these nodes

Always leaf nodes

Single method added to CharacterData

• Text splitText(int offset) throws DOMException

Factory method in Document for creation

Calling normalize() on an Element merges its Text

objects


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CDATASection::Text Interface

Represents CDATA that is not to be interpreted asmarkup (only delimiter recognised is the "]]>" string

that ends the CDATA section)

The DOMString attribute of the Text node holds the

text of the CDATA section

No methods added to CharacterData


• CDATASection newCDATA =

myDoc.createDATASection("press <<<ENTER>>>");


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Comment::Text Interface

Represents comments

all the characters between starting ''

No methods added to CharacterData


• Comment newComment = myDoc.createComment(" my comment "); //Note spaces

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ProcessingInstruction::Node Interface

Represent processing instruction declarations

• Name of node is target application name

• Value of node is target application command


• ProcessingInstruction newPI =

myDoc.createProcessingInstruction("ACME","page-break");

//Get the content of the processing instruction

String getData()

//Set the content of the processing instruction

void setData(String data)

//The target of this processing instructionString getTarget();


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EntityReference::Node Interface

DOM includes interfaces for handling notations, entitiesand entity references

• If the entities have not been replaced by the parser

Element Text

Text

EntityReference Text

An

value

xml

eXtensible

Markup

Language

<!ENTITY xml "eXtensible Markup Language">

<para>An &xml; value</para>

valuename


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Entity::Node Interface

Represents an entity, either parsed or unparsed, in anXML document

• Parser may replace entity references, or createEntityReference nodes

Must retain Entity for non-parsable data

Extends Node interface and adds methods

For non-parsable entities - can get notation name

String getPublicId();

String getSystemId();

String getNotationName();


E i N d I f (2)

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Entity::Node Interface (2)

A parsable Entity may have children that represent

the replacement value of the entity

All entities of a Document accessed with getEntities()method in DocumentType

Entity Text

TextEntityReference

xml

eXtensible

Markup

Languagename

xml

eXtensible

Markup

Language

<!ENTITY MyBoat PUBLIC "BOAT" SYSTEM "boat.gif" NDATA GIF>

String publicId = ent.getPublicId(); //BOAT

String systemId = ent.getSystemId(); //boat.gif

String notation = ent.getNotationName(); //GIF


N t ti N d I t f

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Notation::Node Interface

Each notation declaration in DTD represented by a Notation node

Methods added to Node interface

All notations of a Document accessed withgetNotations() method in DocumentType object

//Returns content of PUBLIC identifier

String getPublicId();

//Returns content of SYSTEM identifier

String getSystemId();


N d Li t I t f

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NodeList Interface

Holds collection of ordered Node objects

Two methods

//Find number of Nodes in NodeListint getLength();

//Return the i-th Node

Node item(int index);

------------------------------------------------- Node child;

NodeList children = element.getChildNodes()'

for (int i = 0; i < children.getLength(); i++) {

child = children.item(i);

if (child.getNodeType() == Node.ELEMENT_NODE) {System.out.println(child.getNodeName());

}

}


N dN d M I t f

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NamedNodeMap Interface

Holds collection of unordered Node objects

• E.g. Attribute, Entity and Notation

Unique names are essential as nodes are accessed byname

NamedNodeMap myAttributes = myElement.getAttributes();

NamedNodeMap myEntities = myDocument.getEntities(); NamedNodeMap myNotations = myDocument.getNotations();

------------------------------------------------------

int getLength();

Node item(int index);

Node getNamedItem(String name); Node setNamedItem(Node node) throws DOMException;//Node!

Node removeNamedItem(String name) throws DOMException;


DocumentFragment::Node Interface

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DocumentFragment::Node Interface

Fragment of Document can be temporarily stored inDocumentFragment node

• Lightweight object, e.g. for 'cut-n-paste'

When attached to another Node - destroys itself (very

useful for adding siblings to tree)

DocumentFragment

DOM tree

New DOM tree


DOMImplementation Interface

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DOMImplementation Interface

Interface to determine level of support in DOM parser• hasFeature(String feature, String version);

• if (theParser.hasFeature("XML", "1.0") {

//XML is supported…

}


DOM Objects

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DOM Objects

DOM object⇔ compiled XML

Can save time and effort if send and receive DOM objectsinstead of XML source

• Saves having to parse XML files into DOM at sender and receiver

• But, DOM object may be larger than XML source


DOM versus XSL

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DOM versus XSL

If you want to do complicated sorting orrestructuring that's beyond the realm of XSL,use DOM

In this method, you parse the XMLdocument, then write Java code to

manipulate the DOM tree in whatever wayyou wish. Your code has complete access tothe DOM and all of its methods, so you're notbound by the limitations or design decisionsof XSL


DOM and XSL

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DOM and XSL

An XSL processor can transform an input XML documentto an XML or HTML output document based on rules in asecond XML document

• A DOM implementation of XSL/XSLT such as LotusXSL processoris useful here

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Info

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Info

Course name:

Special Selected Topic in

Information System

Section: Document Object Model 1.0

Number of slides: 53

Updated date: 12/02/2006

Contact: Mr.Phan Vo Minh Thang

([email protected])

07 - XML - DOM

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