XML is a markup language similar to HTML but designed for structured data rather than web pages. It uses tags to define elements and attributes, and can be validated using DTDs or XML schemas. XML documents can be transformed and queried using XSLT and XPath respectively. SAX is an event-based parser that reads XML sequentially while DOM loads the entire document into memory for random access.

1. Introduction to XML
• XML is a extensible markup language like
HTML.
• The only difference between XML and HTML is
that XML is used for documents containing
structured information.
• Structured information contains both content and
some indication of what role that content
performs.
• XML is basically designed to describe data, it
contains no pre-defined tag, and you must
define your own tag in it.
• It uses DTD and XML schema to describe the
data.

2. Syntax
• Extensible Markup Language (XML) is a set of rules
for encoding documents in machine-readable form.
• All XML Elements Must Have a Closing Tag:
– In HTML, some elements do not have to have a closing tag:
– <p>This is a paragraph
<p>This is another paragraph. In XML, it is illegal to omit the
closing tag. All elements must have a closing tag:
– <p>This is a paragraph</p>
<p>This is another paragraph</p>
• XML Tags are Case Sensitive:
– XML tags are case sensitive. The tag <Letter> is different from
the tag <letter>.
– Opening and closing tags must be written with the same case:
– <Message>This is incorrect</message>
<message>This is correct</message>

3. • XML Elements Must be Properly Nested:
– In HTML, you might see improperly nested elements:
<b><i>This text is bold and italic</b></i>
In XML, all elements must be properly nested within each other:
<b><i>This text is bold and italic</i></b>
• XML Documents Must Have a Root Element:
– XML documents must contain one element that is the parent of all other
elements. This element is called the root element.
– <root>
<child>
<subchild>.....</subchild>
</child>
</root>
• XML Attribute Values Must be Quoted:
– XML elements can have attributes in name/value pairs just like in HTML.
– In XML, the attribute values must always be quoted.
– Study the two XML documents below. The first one is incorrect, the second is
correct:
– <note date=12/11/2007>
<to>Tove</to>
<from>Jani</from>
</note>
– <note date="12/11/2007">
<to>Tove</to>
<from>Jani</from>
</note>

4. • Entity References:
– Some characters have a special meaning in XML.
– If you place a character like "<" inside an XML
element, it will generate an error because the parser
interprets it as the start of a new element.
– This will generate an XML error:
<message>if salary < 1000 then</message>
– To avoid this error, replace the "<" character with an
entity reference:
<message>if salary &lt; 1000 then</message>
– There are 5 predefined entity references in XML:

5. &lt; < Less than
&gt; > Greater than
&amp; & ampersand
&quot “” quotation mark

6. • Comments in XML
– The syntax for writing comments in XML is similar to that of
HTML.
– <!-- This is a comment -->
• White-space is Preserved in XML
– HTML truncates multiple white-space characters to one single
white-space
– HTML: Hello Tove
– Output: Hello Tove
– With XML, the white-space in a document is not truncated
• XML Stores New Line as LF:
– In Windows applications, a new line is normally stored as a pair
of characters: carriage return (CR) and line feed (LF). In Unix
applications, a new line is normally stored as an LF character.
Macintosh applications also use an LF to store a new line.
– XML stores a new line as LF.

7. DTDs and XML Schema
• The purpose of a DTD is to define the
legal building blocks of an XML document.
• It defines the document structure with a
list of legal elements.
• A DTD can be declared inline in your XML
document, or as an external reference.
• Internal DTD
– This is an XML document with a Document
Type Definition

8. <?xml version="1.0"?>
<!DOCTYPE note [
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>
<note>
<to>Tove</to> <from>Jani</from>
<heading>Reminder</heading>
<body>Meeting Tomorrow at 5 p.m</body>
</note>
In XML DTD, #PCDATA is the keyword to specify
mixed content, meaning an element may contain
character data.

9. • The DTD is interpreted like this:
!ELEMENT note (in line 2) defines the
element "note" as having four elements:
"to,from,heading,body".
!ELEMENT to (in line 3) defines the "to"
element to be of the type "CDATA".
!ELEMENT from (in line 4) defines the
"from" element to be of the type "CDATA"

10. • External DTD
– This is the same XML document with an external DTD
<?xml version="1.0"?>
<!DOCTYPE note SYSTEM "note.dtd">
<note>
<to>Tove</to> <from>Jani</from> <heading>Reminder</heading>
<body>Meeting Tomorrow at 5 p.m!</body>
</note>
– This is a copy of the file "note.dtd" containing the Document
Type Definition:
<?xml version="1.0"?>
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>

11. • Why use a DTD?
– XML provides an application independent way of
sharing data.
– With a DTD, independent groups of people can agree
to use a common DTD for interchanging data.
– Your application can use a standard DTD to verify
that data that you receive from the outside world is
valid.
– You can also use a DTD to verify your own data

12. XML Schema
• An XML Schema describes the structure of an XML
document.
• XML Schema is an XML-based alternative to DTD.
• The XML Schema language is also referred to as XML
Schema Definition (XSD).
• The purpose of an XML Schema is to define the legal
building blocks of an XML document, just like a DTD.
– defines elements that can appear in a document
– defines attributes that can appear in a document
– defines which elements are child elements
– defines the order of child elements
– defines the number of child elements
– defines whether an element is empty or can include text
– defines data types for elements and attributes
– defines default and fixed values for elements and attributes

13. XML Schemas are the Successors of DTDs
• We think that very soon XML Schemas will
be used in most Web applications as a
replacement for DTDs. Here are some
reasons:
– XML Schemas are extensible to future
additions
– XML Schemas are richer and more powerful
than DTDs
– XML Schemas are written in XML
– XML Schemas support data types
– XML Schemas support namespaces

14. • <?xml version="1.0"?>
<xs:schema >
<xs:element name="note">
<xs:complexType>
<xs:sequence>
<xs:element name="to" type="xs:string"/>
<xs:element name="from" type="xs:string"/>
<xs:element name="heading" type="xs:string"/>
<xs:element name="body" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
• xsi:noNamespaceSchemaLocation=“Note.xs“
– insert into the root element of the XML document

15. • When defining XML Schema, the content you wish to put
into an XML document must first be summarized. The
next step is to create a tree structure.
– Content to put into the XML document:
• The root element is "Employee_Info"
• As the content for "Employee_Info," "Employee" occurs 0 or more
times
• As content of "Employee," "Name," "Department," "Telephone," and
"Email" elements occur once in respective order
• "Name," "Department," "Telephone," and "Email" content are text
strings
• "Employee" has an attribute called "Employee_Number"
• "Employee_Number" content must be int type

16. XPath
• XPath is used to navigate through
elements and attributes in an XML
document.
• XPath, the XML Path Language, is a
query language for selecting nodes
from an XML document
• XPath includes over 100 built-in functions.
There are functions for string values,
numeric values, date and time
comparison, Boolean values, and more.

17. <?xml version="1.0" encoding="ISO-8859-1"?>
<catalog>
<cd country="USA">
<title>Empire Burlesque</title>
<artist>Bob Dylan</artist>
<price>10.90</price>
</cd>
<cd country="UK">
<title>Hide your heart</title>
<artist>Bonnie Tyler</artist>
<price>10.0</price>
</cd>
<cd country="USA">
<title>Greatest Hits</title>
<artist>Dolly Parton</artist>
<price>9.90</price>
</cd>
</catalog>

18. using System.Xml;
using System.Xml.XPath;
....
string fileName = "data.xml";
XPathDocument doc = new XPathDocument(fileName);
XPathNavigator nav = doc.CreateNavigator();
// Compile a standard XPath expression
XPathExpression expr;
expr = nav.Compile("/catalog/cd[price>=10.0]/price");
XPathNodeIterator iterator = nav.Select(expr);
// Iterate on the node set
listBox1.Items.Clear();
try
{
while (iterator.MoveNext())
{
XPathNavigator nav2 = iterator.Current.Clone();
listBox1.Items.Add("price: " + nav2.Value);
}
}
catch(Exception ex)
{
Console.WriteLine(ex.Message);
}

19. /catalog/cd[1] selects the first cd child of
catalog
/catalog/cd[last()] selects the last cd child of
catalog
/catalog/cd[price] selects all the cd elements that
have price
/
catalog/cd[price=
10.90]
selects cd elements with the
price of 10.90
/
catalog/cd[price=
10.90]/price
selects all price elements with
the price of 10.90

20. • What is XSLT
– Extensible Stylesheet Language
Transformation
– Name is misleading
– Stylesheet
• implies it makes things look like something
• not necessarily or usually true
Name should have been
• “The XML Transformation Language”

21. • What XSLT Does is “Transform”
– Transform means change
Reads XML documents and writes
– HTML for browsers
– interchange file (RTF, RDF, EDI, etc.)
– a flat ASCII file (plain text, comma separated
etc.)

22. • Transform It into HTML (convert to
HTML and display in a browser)

23. • Transform It into PDF (convert to PDF
and display with Acrobat)
• Transform It into QuarkXPress
• Transform It into a Database Load File
– Key: 00095AUS
– EMPNO: 009
– 001:USDIN
– 002:Sasparilla
– 008:36
– 014:70
– 020:Deputy in Charge of Chewables

24. Logical Components of an XSLT
Application
• (needs XSLT processing software
called an “XSLT Engine”)
• Reads XML document(s) (tags and text)
• Uses an XSLT stylesheet/transform (the
program)
• Runs using XSLT processing software
(called an XSLT Engine)
• Produces output document(s)

25. Structure of an XSLT System

26. XMLXSLT.xml
<?xml version="1.0" encoding="utf-8" ?>
<?xml-stylesheet type="text/xsl" href="XSLTFile.xsl" ?>
<employee>
<demo>Look</demo>
<demo>Formatting</demo>
<demo>XML</demo>
<demo>as a HTML</demo>
</employee>

27. XSLTFile.xsl
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match ="/">
<html>
<head>
<titel>XSLT Test</titel>
</head>
<body>
<xsl:for-each select ="employee/demo">
<h1>
<xsl:value-of select ="."/>
</h1>
</xsl:for-each>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

28. • The next element, <xsl:stylesheet>, defines
that this document is an XSLT style sheet
document (along with the version number and
XSLT namespace attributes).
• The <xsl:template> element defines a template.
The match="/" attribute associates the template
with the root of the XML source document.
• The content inside the <xsl:template> element
defines some HTML to write to the output.
• The last two lines define the end of the template
and the end of the style sheet.
• The <xsl:value-of> element can be used to
extract the value of an XML element and add it
to the output stream of the transformation:

29. • We can also filter the output from the XML
file by adding a criterion to the select
attribute in the <xsl:for-each> element.
<xsl:for-each
select="catalog/cd[artist='Bob Dylan']">

30. Table format of xslt file
<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<html>
<body>
<h2>My CD Collection</h2>
<table border="1">
<tr bgcolor="#9acd32">
<th>Title</th>
<th>Artist</th>
</tr>
<tr>
<td><xsl:value-of select="catalog/cd/title"/></td>
<td><xsl:value-of select="catalog/cd/artist"/></td>
</tr>
</table>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

31. Sax and DOM
• SAX (Simple API for XML) is an event-based
sequential access parser API.
• It provides a mechanism of reading data
from xml.
• parsing means syntactic analysis, is the process
of analyzing a text, made of a sequence of
tokens (for example, words), to determine its
grammatical structure with respect to a given
(more or less) formal grammar.
• SAX provides a mechanism for reading data
from an XML document that is an alternative to
that provided by the Document Object Model
(DOM).

32. Benefits of Sax over DOM
• SAX parsers have certain benefits over DOM-style
parsers.
• The quantity of memory that a SAX parser must use in
order to function is typically much smaller than that of a
DOM parser.
• DOM parsers must have the entire tree in memory
before any processing can begin, so the amount of
memory used by a DOM parser depends entirely on the
size of the input data.
• Because of the event-driven nature of SAX, processing
documents can often be faster than DOM-style parsers.
– Memory allocation takes time, so the larger memory footprint of
the DOM is also a performance issue.
• Processing XML documents larger than main memory is
also impossible with DOM parsers, but can be done with
SAX parsers.

33. DOM
• The XML DOM defines a standard way for
accessing and manipulating XML
documents.
• It also provides an application
programming interface for working with
XML data.
• The DOM is designed to be used with any
programming language. such as C/C++,
Visual Basic, VBScript, and JScript.