Unit iv xml dom

Description about XML DOM

1. 6.0 XML DOM By Dr.Smitha.P.S Associate Professor Velammal Engineering College

2. The Document Object Model (DOM) is a programming API for HTML and XML documents. It defines the logical structure of documents and the way a document is accessed and manipulated. With the Document Object Model, programmers can create and build documents, navigate their structure, and add, modify, or delete elements and content. Anything found in an HTML or XML document can be accessed, changed, deleted, or added using the Document Object Model

3. The DOM is a W3C (World Wide Web Consortium) standard. The DOM defines a standard for accessing documents: "The W3C Document Object Model (DOM) is a platform and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure, and style of a document.“

4. The XML DOM defines a standard for accessing and manipulating XML documents. The DOM presents an XML document as a tree-structure. The Document Object Model (DOM) is an application programming interface (API) for HTML and XML documents. It defines the logical structure of documents and the way a document is accessed and manipulated. The DOM is separated into 3 different parts / levels: Core DOM - standard model for any structured document XML DOM - standard model for XML documents HTML DOM - standard model for HTML documents

5. What DOM is not DOM is not a mechanism for persisting or storing objects as XML documents. DOM is not a set of data structures;rather it is an object model describing XML elements DOM does not specify what information in a document is relevant or how information should be structured

6. Why do I need DOM To create or modify an XML document programmatically It is possible to process XML documents using simpler techniques such as XSLT

7. Disadvantages of using DOM DOM is memory intensive DOM API is too complex DOM is not practical for small devices such as PDAs and cellular phones DOM LEVELS Level 1 allows traversal of an XML document as well as the manipulation of the content in that document Level 2 extends level1 with additional features such as namespace support,events,ranges.

8. What is the XML DOM? The XML DOM is: A standard object model for XML A standard programming interface for XML Platform- and language-independent A W3C standard The XML DOM defines the objects and properties of all XML elements, and the methods (interface) to access them. In other words: The XML DOM is a standard for how to get, change, add, or delete XML elements.

9. DOM Nodes According to the DOM, everything in an XML document is a node . The DOM says: The entire document is a document node Every XML element is an element node The text in the XML elements are text nodes Every attribute is an attribute node Comments are comment nodes

10. BOOKS.XML <?xml version="1.0" encoding="UTF-8"?> <bookstore>   <book category="cooking">     <title lang="en">Everyday Italian</title>     <author>Giada De Laurentiis</author>     <year>2005</year>     <price>30.00</price>   </book>   <book category="children">     <title lang="en">Harry Potter</title>     <author>J K. Rowling</author>     <year>2005</year>     <price>29.99</price>   </book>   <book category="web">     <title lang="en">XQuery Kick Start</title>     <author>James McGovern</author>     <author>Per Bothner</author>     <author>Kurt Cagle</author>     <author>James Linn</author>     <author>Vaidyanathan Nagarajan</author>     <year>2003</year>     <price>49.99</price>   </book>   <book category="web" cover="paperback">     <title lang="en">Learning XML</title>     <author>Erik T. Ray</author>     <year>2003</year>     <price>39.95</price>   </book> </bookstore>

11. The root node in the XML above is named <bookstore>. All other nodes in the document are contained within <bookstore>. The root node <bookstore> holds four <book> nodes. The first <book> node holds four nodes: <title>, <author>, <year>, and <price>, which contains one text node each, "Everyday Italian", "Giada De Laurentiis", "2005", and "30.00".

12. The XML DOM Node Tree The XML DOM views an XML document as a tree-structure. The tree structure is called a node-tree. All nodes can be accessed through the tree. Their contents can be modified or deleted, and new elements can be created. The node tree shows the set of nodes, and the connections between them. The tree starts at the root node and branches out to the text nodes at the lowest level of the tree:

13. Node Parents, Children, and Siblings The nodes in the node tree have a hierarchical relationship to each other. The terms parent, child, and sibling are used to describe the relationships. Parent nodes have children. Children on the same level are called siblings (brothers or sisters). In a node tree, the top node is called the root Every node, except the root, has exactly one parent node A node can have any number of children A leaf is a node with no children Siblings are nodes with the same parent

14. Xml parser XML Parser provides way how to access or modify data present in an XML document. Java provides multiple options to parse XML document. Following are various types of parsers which are commonly used to parse XML documents.

15. Dom Parser - Parses the document by loading the complete contents of the document and creating its complete hiearchical tree in memory. SAX Parser - Parses the document on event based triggers. Does not load the complete document into the memory. JDOM Parser - Parses the document in similar fashion to DOM parser but in more easier way.

16. StAX Parser - Parses the document in similar fashion to SAX parser but in more efficient way. XPath Parser - Parses the XML based on expression and is used extensively in conjuction with XSLT. DOM4J Parser - A java library to parse XML, XPath and XSLT using Java Collections Framework , provides support for DOM, SAX and JAXP.

17. XML Parser A parser is a piece of program that takes a physical representation of some data and converts it into an in-memory form for the program as a whole to use. Parsers are used everywhere in software. An XML Parser is a parser that is designed to read XML and create a way for programs to use XML.

18. XML parser is a software library or a package that provides interface for client applications to work with XML documents. It checks for proper format of the XML document and may also validate the XML documents. Modern day browsers have built-in XML parsers.

19. the goal of a parser is to transform XML into a readable code. To ease the process of parsing, some commercial products are available that facilitate the breakdown of XML document and yield more reliable results. Some commonly used parsers are listed below: MSXML (Microsoft Core XML Services) : This is a standard set of XML tools from Microsoft that includes a parser. System.Xml.XmlDocument : This class is part of .NET library, which contains a number of different classes related to working with XML. Java built-in parser : The Java library has its own parser. The library is designed such that you can replace the built-in parser with an external implementation such as Xerces from Apache or Saxon. Saxon : Saxon offers tools for parsing, transforming, and querying XML. Xerces : Xerces is implemented in Java and is developed by the famous open source Apache Software Foundation.

20. XML DOM Parser All major browsers have a built-in XML parser to read and manipulate XML. The XML parser converts XML into an XML DOM object that can be accessed with JavaScript. The XML DOM contains methods to traverse XML trees, access, insert, and delete nodes. However, before an XML document can be accessed and manipulated, it must be loaded into an XML DOM object. An XML parser reads XML, and converts it into an XML DOM object that can be accessed with JavaScript. Most browsers have a built-in XML parser.

21. Advantages XML DOM is language and platform independent. XML DOM is traversible - Information in XML DOM is organized in a hierarchy which allows developer to navigate around the hierarchy looking for specific information. XML DOM is modifiable - It is dynamic in nature providing developer a scope to add, edit, move or remove nodes at any point on the tree.

22. Disadvantages It consumes more memory (if the XML structure is large) as program written once remains in memory all the time until and unless removed explicitly. Due to the larger usage of memory its operational speed, compared to SAX is slower

23. PROGRAM 1 <!DOCTYPE html> <html> <head> <script src="loadxmldoc.js"></script> </head> <body> <script> xmlDoc=loadXMLDoc("books.xml"); document.write(xmlDoc.getElementsByTagName("title")[0].childNodes[0].nodeValue + "<br>"); document.write(xmlDoc.getElementsByTagName("author")[0].childNodes[0].nodeValue + "<br>"); document.write(xmlDoc.getElementsByTagName("year")[0].childNodes[0].nodeValue); </script> </body> </html> OUTPUT: Everyday Italian Giada De Laurentiis 2005

24. XML DOM Properties These are some typical DOM properties: x.nodeName - the name of x x.nodeValue - the value of x x.parentNode - the parent node of x x.childNodes - the child nodes of x x.attributes - the attributes nodes of x

25. XML DOM Methods x.getElementsByTagName( name ) - get all elements with a specified tag name x.appendChild( node ) - insert a child node to x x.removeChild( node ) - remove a child node from x

26. You can access a node in three ways: 1. By using the getElementsByTagName() method 2. By looping through (traversing) the nodes tree. 3. By navigating the node tree, using the node relationships.

27. The getElementsByTagName() Method getElementsByTagName() returns all elements with a specified tag name. Syntax node .getElementsByTagName( "tagname" );

28. DOM Node List Length The length property defines the length of a node list (the number of nodes). You can loop through a node list by using the length property:

29. PROGRAM2 <!DOCTYPE html> <html> <head> <script src="loadxmldoc.js"></script> </head> <body> <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName("title"); for (i=0;i<x.length;i++) { document.write(x[i].childNodes[0].nodeValue); document.write("<br>"); } </script> </body> </html> OUTPUT Everyday Italian Harry Potter XQuery Kick Start Learning XML

30. Traversing Nodes The following code loops through the child nodes, that are also element nodes, of the root node: Example var xmlDoc=loadXMLDoc("books.xml"); var x=xmlDoc.documentElement.childNodes; for (i=0;i<x.length;i++)   {   // Process only element nodes (type 1)   if (x[i].nodeType==1)     {     document.write(x[i].nodeName);     document.write("<br>");     }   } OUTPUT book book book book

31. Navigating Node Relationships The following code navigates the node tree using the node relationships: <!DOCTYPE html> <html> <head> <script src="loadxmldoc.js"></script> </head> <body> <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName("book")[0].childNodes; y=xmlDoc.getElementsByTagName("book")[0].firstChild; for (i=0;i<x.length;i++) { if (y.nodeType==1) {//Process only element nodes (type 1) document.write(y.nodeName + "<br>"); } y=y.nextSibling; } </script> </body> </html> Output title author year price

32. Node Properties In the XML DOM, each node is an object . Objects have methods and properties, that can be accessed and manipulated by JavaScript. Three important node properties are: nodeName nodeValue nodeType

33. The nodeName Property The nodeName property specifies the name of a node. nodeName is read-only nodeName of an element node is the same as the tag name nodeName of an attribute node is the attribute name nodeName of a text node is always #text nodeName of the document node is always #document

34. The nodeValue Property The nodeValue property specifies the value of a node. nodeValue for element nodes is undefined nodeValue for text nodes is the text itself nodeValue for attribute nodes is the attribute value

35. Get the Value of an Element The following code retrieves the text node value of the first <title> element: Example <!DOCTYPE html> <html> <head> <script src="loadxmldoc.js"></script> </head> <body> <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName("title")[0] y=x.childNodes[0]; document.write(y.nodeValue); </script> </body> </html> OUTPUT Everyday Italian

36. The getAttribute() method returns an attribute value . <!DOCTYPE html> <html> <head> <script src="loadxmldoc.js"> </script> </head> <body> <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName('book'); for (i=0;i<x.length;i++) { document.write(x[i].getAttribute('category')); document.write("<br>"); } </script> </body> </html> Output cooking children web web

37. The getAttributeNode() method returns an attribute node . <!DOCTYPE html> <html> <head> <script src="loadxmldoc.js"> </script> </head> <body> <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName("title")[0].getAttributeNode("lang"); txt=x.nodeValue; document.write(txt); </script> </body> </html> OUTPUT En

38. Change the Value of an Element The following code changes the text node value of the first <title> element: Example <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName("title")[0].childNodes[0]; x.nodeValue="Easy Cooking"; document.write(x.nodeValue); </script> OUTPUT : Easy Cooking

39. Change an Attribute Using setAttribute() The setAttribute() method changes the value of an existing attribute, or creates a new attribute. The following code changes the category attribute of the <book> element: Example <script> xmlDoc=loadXMLDoc("books.xml"); x=xmlDoc.getElementsByTagName('book'); x[0].setAttribute("category","food"); document.write(x[0].getAttribute("category")); </script> OUTPUT: FOOD

40. removeChild() and replaceChild() The removeChild() method removes a specified node. When a node is removed, all its child nodes are also removed Replace an Element Node The replaceChild() method is used to replace a node.

41. EXAMPLE //create a book element, title element and a text node newNode=xmlDoc.createElement("book"); newTitle=xmlDoc.createElement("title"); newText=xmlDoc.createTextNode("A Notebook"); //add the text node to the title node, newTitle.appendChild(newText); //add the title node to the book node newNode.appendChild(newTitle); y=xmlDoc.getElementsByTagName("book")[0] //replace the first book node with the new node x.replaceChild(newNode,y); z=xmlDoc.getElementsByTagName("title"); for (i=0;i<z.length;i++) { document.write(z[i].childNodes[0].nodeValue); document.write("<br>"); } </script> </body> </html>

42. OUTPUT A Notebook Harry Potter XQuery Kick Start Learning XML