XML-INTRODUCTION.pdf

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XML
Extensible Markup Language
Prepared By: Dr.Saranya.K.G
SGML (Standard Generalized
Markup Language)
• It is an internationally agreed standard for data representation.
• It is an international standard for the definition of device
independent, system independent methods of representing texts
in electronic form.

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Introduction
• XML stands for EXtensible Markup Language
• XML is a markup language much like HTML. A markup language is
used to provide information about a document.
• A simplified version of SGML
• More flexible and adaptable than HTML
• XML was designed to describe data
• Tags are added to the document to provide the extra
information.
• HTML tags tell a browser how to display the document.
• XML tags give a reader some idea what some of the data
means.
• XML tags are not predefined. You must define your own tags
• XML uses a Document Type Definition (DTD) or an XML
Schema to describe the data

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• XML was designed to store and transport data.
• XML was designed to be both human- and machine-readable.
• XML is often used for distributing data over the Internet.
• XML is a W3C Recommendation.
• World Wide Web Consortium published the first XML 1.0 standard
definition in 1998.
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!
</body>
</note>
The XML above is quite self-descriptive:
• It has sender information.
• It has receiver information
• It has a heading
• It has a message body.
But still, the XML above does not DO anything. XML is just information
wrapped in tags.
Note
To: Tove
From: Jani
Reminder
Don't forget me
this weekend!

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XML Does Not Use Predefined Tags
• The XML language has no predefined tags.
• The tags in the example above (like <to> and <from>) are not defined
in any XML standard. These tags are "invented" by the author of the
XML document.
• HTML works with predefined tags like <p>, <h1>, <table>, etc.
• With XML, the author must define both the tags and the document
structure.
XML is Extensible
• Most XML applications will work as expected even if new data is added
(or removed).
• Imagine an application designed to display the original version of note.xml
(<to> <from> <heading> <body>).
• Then imagine a newer version of note.xml with added <date> and <hour>
elements, and a removed <heading>.
• The way XML is constructed, older version of the application can still
work:

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<note>
<date>2015-09-01</date>
<hour>08:30</hour>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this
weekend!</body>
</note>
Older Version
Note
To: Tove
From: Jani
Reminder
Don't forget me this weekend!
New Version
Note
To: Tove
From: Jani
Date: 2015-09-01 08:30
<note>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this
weekend! </body>
</note>
XML Simplifies Things
• It simplifies data sharing
• It simplifies data transport
• It simplifies platform changes
• It simplifies data availability
Many computer systems contain data in incompatible formats. Exchanging data between incompatible systems (or
upgraded systems) is a time-consuming task for web developers. Large amounts of data must be converted, and
incompatible data is often lost.
XML stores data in plain text format. This provides a software- and hardware-independent way of storing, transporting,
and sharing data.
XML also makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without
losing data.
With XML, data can be available to all kinds of "reading machines" like people, computers, voice machines, news feeds,
etc. Prepared By: Dr.Saranya.K.G

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XML is a W3C Recommendation
XML Separates Data from Presentation
• XML does not carry any information about how to be displayed.
• The same XML data can be used in many different presentation
scenarios.
• Because of this, with XML, there is a full separation between data and
presentation.
XML is Often a Complement to HTML
In many HTML applications, XML is used to store or transport data, while HTML is used
to format and display the same data.
XML Separates Data from HTML
• When displaying data in HTML, you should not have to edit the HTML file
when the data changes.
• With XML, the data can be stored in separate XML files.
• With a few lines of JavaScript code, you can read an XML file and update the
data content of any HTML page.

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Difference between XML and HTML
The main difference between XML and HTML
• XML was designed to carry data. (XML is not a replacement for HTML)
XML and HTML were designed with different goals:
• XML was designed to describe data and to focus on what data is.
HTML was designed to display data and to focus on how data looks.
• HTML is about displaying information, while XML is about describing
information.
• XML tags are not predefined like HTML tags are
What is XML Used For?
• XML documents are used to transfer data from one place to another often over the
Internet.
• XML subsets are designed for particular applications.
• One is RSS (Rich Site Summary or Really Simple Syndication ). It is used to send
breaking news bulletins from one web site to another.
• A number of fields have their own subsets. These include chemistry, mathematics,
and books publishing.
• Most of these subsets are registered with the W3Consortium and are available for
anyone’s use. Prepared By: Dr.Saranya.K.G

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Why Is XML Important?
• Plain Text
• Easy to edit
• Possible to efficiently store large amounts of XML data through an XML
front end to a database
• Data Identification
• Tell you what kind of data you have
• Can be used in different ways by different applications
Why is XML important?
• Linkability -- XLink and XPointer
• Simple unidirectional hyperlinks
• Two-way links
• Multiple-target links
• “Expanding” links
• Easily Processed
• Regular and consistent notation
• Hierarchical
• Faster to access
• Easier to rearrange

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Advantages of XML
• XML is text (Unicode) based.
• Takes up less space.
• Can be transmitted efficiently.
• One XML document can be displayed differently in different media.
• Html, video, CD, DVD,
• You only have to change the XML document in order to change all the rest.
• XML documents can be modularized. Parts can be reused.
XML Specifications
•XML 1.0
Defines the syntax of XML
•XPointer, XLink
Defines a standard way to represent links between resources
•XSL
Defines the standard style sheet language for XML

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XML Tree Structure
XML Structure
XML documents form a tree structure that starts at "the root" and branches to "the leaves".
XML Trees
• An XML document has a single root node.
• The tree is a general ordered tree.
• A parent node may have any number of children.
• Child nodes are ordered, and may have siblings.
• Preorder traversals are usually used for getting
information out of the tree.
<root>
<child>
<subchild>.....</subchild>
</child>
</root>

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<?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>
</book>
<book category="web">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
</book>
</bookstore>
Category Title Author Year Price
Cooking Everyday
Italian
Giada De
Laurentiis
2005 30.00
children Harry Potter J K. Rowling 2005 29.99
web Learning XML Erik T. Ray 2003 39.95
Book Store Details:
A prolog defines the XML version and the character encoding:
The next line is the root element of the document:
<bookstore>
The next line starts a <book> element:
<book category="cooking">

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The <book> elements have 4 child elements: <title>, <author>, <year>, <price>.
<title lang="en">Everyday
Italian</title>
<author>Giada De
Laurentiis</author>
<year>2005</year>
The next line ends the book element:
</book>
Expanded Example
<?xml version = “1.0” ?>
<address>
<name>
<first> Alice </first>
<last> Lee </last>
</name>
<email> alee@aol.com </email>
<phone> 123-45-6789 </phone>
<birthday>
<year> 1983 </year>
<month> 07 </month>
<day> 15 </day>
</birthday>
</address>

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XML Files are Trees
address
name email phone birthday
first last year month day
XML SYNTAX

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XML Syntax Rules
The syntax rules of XML are very simple and logical. The rules are easy to learn, and easy
to use.
1. XML Documents Must Have a Root Element
XML documents must contain one root element that is the parent of all other elements:
<root>
<child>
<subchild>.....</subchild>
</child>
</root>
In this example <note> is the root element:
<note>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this weekend!</body>
</note>
Example

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The XML Prolog
The above line is called as the XML prolog
• The XML prolog is optional. If it exists, it must come first in the document.
• XML documents can contain international characters, like Norwegian øæå or
French êèé.
• To avoid errors, you should specify the encoding used, or save your XML files as
UTF-8.
• UTF-8 is the default character encoding for XML documents.
2. All XML Elements Must Have a Closing Tag
<p>This is a paragraph.</p>
<br />
The XML prolog does not have a closing tag! This is not an error. The prolog is not a
part of the XML document.

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3. 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 correct</message>
"Opening and closing tags" are often referred to as "Start and end tags". Use
whatever you prefer. It is exactly the same thing.
4. 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>
In the example above, "Properly nested" simply means that since the <i> element is
opened inside the <b> element, it must be closed inside the <b> element.

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5. XML Attribute Values Must Always be Quoted
• XML elements can have attributes in name/value pairs just like in HTML.
In XML, the attribute values must always be quoted:
<note date="12/11/2007“>
<to>Tove</to>
<from>Jani</from>
</note>
6. 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> salary < 1000 </message>
To avoid this error, replace the "<" character with an entity reference:

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<message> salary < 1000 </message>
There are 5 pre-defined entity references in XML:
< < less than
> > greater than
& & ampersand
' ' apostrophe
" " quotation mark
Only < and & are strictly illegal in XML, but it is a good habit to replace > with >
as well.
7. Comments in XML
The syntax for writing comments in XML is similar to that of HTML:

Two dashes in the middle of a comment are not allowed:

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8. White-space is Preserved in XML
• XML does not truncate multiple white-spaces (HTML truncates multiple
white-spaces to one single white-space):
XML: Hello Tove
HTML: Hello Tove
9. XML Stores New Line as LF
• Windows applications store a new line as: carriage return and line
feed (CR+LF).
• Unix and Mac OSX uses LF.
• Old Mac systems uses CR.
• XML stores a new line as LF.

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XML Syntax (Summary)
• XML declaration is the first statement. (Prolog)
• All XML elements must have a closing tag
• XML tags are case sensitive
• All XML elements must be properly nested
• All XML documents must have a root tag
• Attribute values must always be quoted
• With XML, white space is preserved
• Comments in XML: 
• Certain characters are reserved for parsing
XML Elements

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What is an XML Element?
• An XML element is everything from (including) the element's start tag to
(including) the element's end tag.
An element can contain:
• text
• attributes
• other elements
• or a mix of the above
<bookstore>
<book category="children">
<title>Harry Potter</title>
<author>J K.
Rowling</author>
<year>2005</year>
</book>
<book category="web">
<title>Learning XML</title>
<author>Erik T.
Ray</author>
<year>2003</year>
</book>
</bookstore> Prepared By: Dr.Saranya.K.G

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In the example above:
<title>, <author>, <year>, and <price> have text content because they
contain text (like 29.99).
<bookstore> and <book> have element contents, because they contain
elements.
<book> has an attribute (category="children").
Empty XML Elements
• An element with no content is said to be empty.
• In XML, you can indicate an empty element like this:
<element></element>
You can also use a so called self-closing tag:
<element />
Empty elements can have attributes.

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XML Naming Rules
XML elements must follow these naming rules:
• Element names are case-sensitive
• Element names must start with a letter or underscore
• Element names cannot start with the letters xml (or XML, or Xml, etc)
• Element names can contain letters, digits, hyphens, underscores, and
periods
• Element names cannot contain spaces
• Any name can be used, no words are reserved (except xml).
Best Naming Practices
• Create descriptive names, like this: <person>, <firstname>, <lastname>.
• Create short and simple names, like this: <book_title> not like this:
<the_title_of_the_book>.
• Avoid "-". If you name something "first-name", some software may think you want to
subtract "name" from "first".
• Avoid ".". If you name something "first.name", some software may think that "name" is a
property of the object "first".
• Avoid ":". Colons are reserved for namespaces (more later).
• Non-English letters like éòá are perfectly legal in XML, but watch out for problems if your
software doesn't support them.

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Naming Styles
Style Example Description
Lower case <firstname> All letters lower case
Upper case <FIRSTNAME> All letters upper case
Underscore <first_name> Underscore separates words
Pascal case <FirstName> Uppercase first letter in each word
Camel case <firstName>
Uppercase first letter in each word except
the first
• If you choose a naming style, it is good to be consistent!
• XML documents often have a corresponding database. A common practice is to
use the naming rules of the database for the XML elements.
• Camel case is a common naming rule in JavaScripts.
XML Elements are Extensible
• XML elements can be extended to carry more information.
Look at the following XML example:
<note>
<to>Tove</to>
<from>Jani</from>
</note>

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Let's imagine that we created an application that extracted the <to>, <from>, and
<body> elements from the XML document to produce this output:
MESSAGE To: Tove
From: Jani
Imagine that the author of the XML document added some extra information to it
<note>
<date>2008-01-10</date>
<to>Tove</to>
<from>Jani</from>
</note>
• Should the application break or crash?
• No. The application should still be able to find the <to>, <from>,
and <body> elements in the XML document and produce the
same output.
• This is one of the beauties of XML. It can be extended without
breaking applications.

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XML Attributes
• Attributes are designed to contain data related to a specific element.
• XML attributes are used to describe XML elements or to provide
additional information about elements.
• Attributes provide additional information that is not part of the data.
Ex:
<Book no=“99-2456” media=“CD”></Book>
XML Attributes Must be Quoted
• Attribute values must always be quoted. Either single or
double quotes can be used.
• For a person's gender, the <person> element can be written
like this:
<person gender="female">
or like this:
<person gender='female'>

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If the attribute value itself contains double quotes you can use single quotes,
like in this example:
<gangster name='George "Shotgun" Ziegler'>
or you can use character entities:
<gangster name="George "Shotgun" Ziegler">
XML Elements vs. Attributes
<person gender="female">
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>
<person>
<gender>female</gender>
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>
• In the first example gender is an attribute. In the last, gender is an element. Both
examples provide the same information.
• There are no rules about when to use attributes or when to use elements in XML.

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Consider the following three XML documents contain exactly the same information:
A date attribute is used in the first example:
<note date="2008-01-10">
<to>Tove</to>
<from>Jani</from>
</note>
A <date> element is used in the second example:
<note>
<date>2008-01-10</date>
<to>Tove</to>
<from>Jani</from>
</note>
An expanded <date> element is used in the third example:
<note>
<date>
<year>2008</year>
<month>01</month>
<day>10</day>
</date>
<to>Tove</to>
<from>Jani</from>
</note> Prepared By: Dr.Saranya.K.G
Avoid XML Attributes?
Some things to consider when using attributes are:
• attributes cannot contain multiple values (elements can)
• attributes cannot contain tree structures (elements can)
• attributes are not easily expandable (for future changes)
Don't end up like this:
<note day="10" month="01" year="2008"
to="Tove" from="Jani" heading="Reminder"
body="Don't forget me this weekend!">
</note>

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XML Attributes for Metadata
• Sometimes ID references are assigned to elements. These IDs can be
used to identify XML elements in much the same way as the id
attribute in HTML. This example demonstrates this:
<messages>
<note id="501">
<to>Tove</to>
<from>Jani</from>
</note>
<note id="502">
<to>Jani</to>
<from>Tove</from>
<heading>Re: Reminder</heading>
<body>I will not</body>
</note>
</messages>
The id attributes above are for identifying the different notes. It is not a part of the note itself.
Metadata (data about data) should be stored as attributes, and the data itself should be
stored as elements.

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XML Specifications
• XML 1.0
Defines the syntax of XML
• XPointer, XLink
Defines a standard way to represent links between resources
• XSL
Defines the standard stylesheet language for XML
XML Validation
There are two types of XML documents
• "Well Formed" XML document
--correct XML syntax
• "Valid" XML document
• “well formed”
• Conforms to the rules of a DTD (Document Type Definition)
• XML DTD
• defines the legal building blocks of an XML document
• Can be inline in XML or as an external reference
• XML Schema
• an XML based alternative to DTD, more powerful
• Support namespace and data types

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Displaying XML
• XML documents do not carry information about how to
display the data
• We can add display information to XML with
• CSS (Cascading Style Sheets)
• XSL (eXtensible Stylesheet Language) --- preferred
XML support in IE 5.0+
Internet Explorer 5.0 has the following XML support:
• Viewing of XML documents
• Full support for W3C DTD standards
• Binding XML data to HTML elements
• Transforming and displaying XML with XSL
• Displaying XML with CSS
• Access to the XML DOM (Document Object Model)
*Netscape 6.0 also have full XML support

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XML features
• XML uses the concept of document type and hence a DTD (Document
Type Definition) to describe data
• XML with DTD is self descriptive
• XML separates data from display formats
• XML can be used as a format to exchange data
XML Syntax consists of
• XML Declaration
• XML Elements
• XML Attributes
• The first line of an XML document should always consist of an
XML declaration defining the version of XML

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General Structure
<root>
<child>
<subchild>…….</subchild>
</child>
</root>
Main Components of an XML Document
• Elements: <hello>
• Attributes: <item id=“33905”>
• Entities: < (<)
• Advanced Components
• CData Sections
• Processing Instructions

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XML strengths
• Its ability to describe data
• Its ability to structure data
• Separate display from structure
• Supported by industry
• Availability of tools
XML applications
• B2B
• EDI
• Journal publishing
• Database development

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An example of XML
<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
<to>XXX</to>
<from>YYY</from>
<heading>XML</heading>
<body> Extensible Markup Language </body>
</note>
Contents of the ProductList.xml Document

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• The first line represents the XML document declaration and it is
mandatory.
• Every XML has a root element. In our example, the second line is
the root element - <ProductList>
• The root element can contain child elements. In our example,
Product is the child element of ProductList
• Each element can contain sub-elements.
• <P_CODE>,<P_PRICE> are sub-elements.
Example
<?xml version="1.0" encoding= "ISO-8859-1" ?>
<book>
<title> XML </title>
<chapter> introduction to xml
<para>Markup languages</para>
<para>Features of XML</para>
</chapter>
<chapter>XML syntax
<para>Elements must be enclosed in tags</para>
<para>Elements must be properly nested</para>
</chapter>
</book>

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XML Architecture
How do you get the data?
XML
data
Parser Information
structure
(tree+links)
Documents, stylesheets, and other data can all be expressed in XML.
DOM Interface
Any application can
plug in via an API
called “Document
Object Model”
DTD/Schema
This model can work locally or over a network.
Parsing, tree-building, and access can shift between
client/server

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XML Parser
• All modern browsers have a built-in XML parser.
• An XML parser converts an XML document into an XML DOM object -
which can then be manipulated with a JavaScript.
XML DOM
• A DOM (Document Object Model) defines a standard way for accessing
and manipulating XML documents.
XML Namespaces
• XML Namespaces provide a method to avoid element name conflicts.
• This XML carries HTML table information:
<table>
<tr>
<td>Apples</td>
<td>Bananas</td>
</tr>
</table>

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• This XML carries information about a table (a piece of furniture):
<table>
<name>African Coffee Table</name>
<width>80</width>
<length>120</length>
</table>
• If these XML fragments were added together, there would be a name
conflict.
• Both contain a <table>element, but the elements have different content
and meaning.
• An XML parser will not know how to handle these differences.
Solving the Name Conflict Using a Prefix
• Name conflicts in XML can easily be avoided using a name prefix.
• This XML carries information about an HTML table, and a piece of furniture:
<h:table>
<h:tr>
<h:td>Apples</h:td>
<h:td>Bananas</h:td>
</h:tr>
</h:table>
<f:table>
<f:name>African Coffee Table</f:name>
<f:width>80</f:width>
<f:length>120</f:length>
</f:table> Prepared By: Dr.Saranya.K.G

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• In the example above, there will be no conflict because the
two <table> elements have different names.
XML Namespaces - The xmlns Attribute
• When using prefixes in XML, a so-called namespace for the prefix
must be defined.
• The namespace is defined by the xmlns attribute in the start tag
of an element.
• The namespace declaration has the following syntax.
xmlns:prefix="URI".

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<root>
<h:table xmlns:h="http://www.w3.org/TR/html4/">
<h:tr>
<h:td>Apples</h:td>
<h:td>Bananas</h:td>
</h:tr>
</h:table>
<f:table xmlns:f="http://www.w3schools.com/furniture">
<f:name>African Coffee Table</f:name>
<f:width>80</f:width>
<f:length>120</f:length>
</f:table>
</root>
XML Namespaces - The xmlns Attribute
• In the example above, the xmlns attribute in the <table> tag give the
h: and f: prefixes a qualified namespace.
• When a namespace is defined for an element, all child elements
with the same prefix are associated with the same namespace.
• Namespaces can be declared in the elements where they are used or
in the XML root element:

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URI
• Uniform Resource Identifier (URI)
• A Uniform Resource Identifier (URI) is a string of characters which identifies
an Internet Resource.
• The most common URI is the Uniform Resource Locator (URL) which identifies
an Internet domain address. Another, not so common type of URI is the
Universal Resource Name (URN).
PCDATA - Parsed Character Data
• XML parsers normally parse all the text in an XML document.
• When an XML element is parsed, the text between the XML tags is
also parsed:
<message>This text is also parsed</message>

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<name><first>Bill</first><last>Gates</last></name>
The parser does this because XML elements can contain other elements, as in
this example, where the <name> element contains two other elements (first
and last): and the parser will break it up into sub-elements like this:
<name>
<first>Bill</first>
<last>Gates</last>
</name
Parsed Character Data (PCDATA) is a term used about text data that will be
parsed by the XML parser. Prepared By: Dr.Saranya.K.G
CDATA - (Unparsed) Character Data
• The term CDATA is used about text data that should not be parsed by the XML
parser.
• Characters like "<" and "&" are illegal in XML elements.
• "<" will generate an error because the parser interprets it as the start of a new
element.
• "&" will generate an error because the parser interprets it as the start of an
character entity.
• Some text, like JavaScript code, contains a lot of "<" or "&" characters. To
avoid errors script code can be defined as CDATA.

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• Everything inside a CDATA section is ignored by the parser.
• A CDATA section starts with "<![CDATA[" and ends with "]]>":
<script>
<![CDATA[
function matchwo(a,b)
{
if (a < b && a < 0) then
{
return 1;
}
else
{
return 0;
}
}
]]>
</script>
In this example, everything inside the CDATA section is ignored by the
parser
Conclusion
• XML is a self-descriptive language
• XML is a powerful language to describe structure data for web application
• XML is currently applied in many fields
• Many vendors already supports or will support XML
• XML Documents can be validated through the use of DTD and XSD
documents
• XML impacts B2B data exchanges, legacy system integration, web page
development, database system integration.

XML-INTRODUCTION.pdf

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XML-INTRODUCTION.pdf