XMLin Web development and Applications.pdf

Introduction to XML
◼ XML stands for Extensible Mark-up Language.
◼ XML was designed to store and transport data.
◼ XML was designed to be both human- and machine-readable.
◼ XML is a markup language for documents containing semistructured information.
◼ A W3C (The World Wide Web Consortium) standard to complement HTML.
◼ In HTML, both the tag semantics and the tag set are fixed.
◼ XML tags are not predefined. Users must define their own tags.
◼ Origins: structured text SGML
◼ SGML is the Standard Generalized Markup Language defined by ISO (International
Organization for Standardization), but it is not well suited to serving documents over
the web.
◼ XML is a software- and hardware-independent tool for storing and transporting data.
1. XML is a mark-up language much like HTML
2.XML was designed to store and transport data
3. XML was designed to be self-descriptive.
◼ XML tags identify the data and are used to store and organize the data.
◼ XML is not going to replace HTML in the near future, but it introduces new
possibilities by adopting many successful features of HTML

Why XML?
◼ There are systems with different-different operating systems having
data in different formats. In order to transfer the data between these
systems is a difficult task as the data needs to converted in
compatible formats before it can be used on other system. With
XML, it is so easy to transfer data between such systems as XML
doesn’t depend on platform and the language.
◼ XML is a simple document with the data, which can be used to store
and transfer data between any systems irrespective of their
hardware and software compatibilities.

Characteristics of XML
◼ There are three important characteristics of XML that make it useful
in a variety of systems and solutions:
◼ XML is extensible:
XML allows you to create your own self-descriptive tags, or
language, that suits your application.
◼ XML carries the data, does not present it:
XML allows you to store the data irrespective of how it will be
presented.
◼ XML is a public standard:
XML was developed by an organization called the World Wide
Web Consortium (W3C) and is available as an open standard.

XML Usage
◼ XML can work behind the scene to simplify the creation of HTML
documents for large web sites.
◼ XML can be used to exchange the information between
organizations and systems.
◼ XML can be used for offloading and reloading of databases.
◼ XML can be used to store and arrange the data, which can
customize your data handling needs.
◼ XML can easily be merged with style sheets to create almost any
desired output.
◼ Virtually, any type of data can be expressed as an XML document.

XML VS HTML
XML HTML
The full form is extensible Mark-up Language. The full form is Hypertext Mark-up Language.
The main purpose is to focus on the transport of
data and saving the data.
Focuses on the appearance of data. Enhances the
appearance of text,
XML is dynamic because it is used in the transport
of data.
HTML is static because its main function is in the
display of data.
It is case-sensitive. The upper and lower case needs
to be kept in mind while coding.
It is not case-sensitive. Upper and lower case are of
not much importance in HTML.
You can define tags as per your requirement, but
closing tags are mandatory.
It has its own pre-defined tags, and it is not
necessary to have closing tags.
XML can preserve white spaces. White spaces are not preserved in HTML.
eXtensible Markup Language is content-driven, and
not many formatting features are available.
Hypertext Markup Language, on the other hand, is
presentation driven. How the text appears is of
utmost importance.
Any error in the code shall not give the final
.outcome
Small errors in the coding can be ignored and the
outcome can be achieved
The size of the document may be large No lengthy documents. Only the syntax needs to be
added for best-formatted output.

Key Components OF XML
◼ XML Elements
◼ Declaration
◼ Attributes
◼ Text
◼ Comments
◼ Processing instructions:

Conti…
1. XML Elements :
a. The XML declaration is an optional component that specifies the version of XML
used in the document, as well as the character encoding.
b. It is typically placed at the beginning of an XML document and enclosed in angle
brackets.
2. Elements:
a. Elements are the building blocks of an XML document.
b. They define the structure and meaning of the data in the document.
c. Each element is enclosed in angle brackets and consists of an opening tag, content,
and a closing tag.
d. For example, <title>The Catcher in the Rye</title> is an element with the tag name
"title" and the content "The Catcher in the Rye".

Conti…
3.Attributes:
a. Attributes provide additional information about an element.
b. They are specified within the opening tag of an element and consist of a name and a
value separated by an equals sign.
c. For example, <book isbn="0-316-76953-3"> specifies the attribute "isbn" with the
value "0-314.
4. Text:
a. Text is the content within an element that is not enclosed in other tags.
b. For example, in <title>The Catcher in the Rye</title>, "The Catcher in the Rye" is the
text content of the "title" element.
5. Comments:
a. Comments are used to provide annotations and explanations within an XML
document.
b. They are enclosed in  and are ignored by XML processors.6-76953-3".

Conti..
6. Processing instructions :
a. Processing instructions provide instructions to XML processors for
how to process the document.
b. They are enclosed in <? and ?> and typically provide information
about how to handle the document's content.
• These components work together to define the structure and
meaning of data in an XML document.

XML document:
<?xml version="1.0"?>
<contact_info>
<name>Rajesh</name>
<company>TCS</company>
<phone>9333332354</phone>
</contact_info>
There are two kinds of information in the above example:
1.markup, like <contact-info> and
2.the text, like Rajesh etc.

Simple XML document example
<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
<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">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>

XML Tree Structure
◼ XML documents are formed as element trees.
◼ An XML tree starts at a root element and branches from the root to child
elements.
◼ All elements can have sub elements (child elements):
<root>
<child>
<subchild>.....</subchild>
</child>
</root>
◼ The terms parent, child, and sibling are used to describe the relationships
between elements.
◼ Parents have children. Children have parents. Siblings are children on the
same level (brothers and sisters)

XML Syntax Rules:
The syntax rules of XML are very simple and logical. The rules are easy to learn,
and easy to use.

XML Syntax Rules conti…:
➢ XML declaration:
XML declaration is written as below:
➢ Syntax Rules for XML declaration:
1. The XML declaration is case sensitive and must begin with “ "
where "xml" is written in lower-case.
2. If the document contains XML declaration, then it strictly needs to
be the first statement of the XML document.
3. The XML declaration strictly needs be the first statement in the
XML document.
4. An HTTP protocol can override the value of encoding that you put
in the XML declaration
• In above syntax its define version of XML as prolog option.
• UTF-8 is the default character encoding for XML documents.

2. Tag and Elements
◼ XML documents must contain one root element that is the parent of
all other elements.
Ex: <root>
<x>...</x>
<y>...</y>
</root>
◼ All XML Elements Must Have a Closing Tag.
◼ 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.
◼ Ex: <message>This is correct</message>.
◼ XML Elements Must be Properly Nested
◼ Ex: <b><i>This text is bold and italic</i></b>

3.Attribute
◼ XML Attribute Values Must Always be Quoted.
Ex: <note date="12/11/2007"> </note>
◼ Attribute names in XML (unlike HTML) are case sensitive. That is,
HREF and href are considered two different XML attributes.
◼ Same attribute cannot have two values in a syntax. The following
example shows incorrect syntax because the attribute b is specified
twice:
◼ <a b="x" c="y" b="z">....</a> here b attribute uses two values for
two time which is incorrect.
◼ Attribute names are defined without quotation marks, whereas
attribute values must always appear in quotation marks. Following
example demonstrates incorrect xml syntax:
◼ <a b=x>....</a> it is incorrect, the attribute value is not defined in
quotation marks.

4. REFERANCES
◼ References usually allow you to add or include additional text or markup in
an XMLdocument.
◼ References always begin with the symbol "&" ,which is a reserved character
and end with the symbol ";".
◼ XML has two types of references:
◼ :Entity References
1.An entity reference contains a name between the start and the end
delimiters.
2. For example & where amp is name.
3.The name refers to a predefined string of text and/or markup.
4.Ex: <message>salary < 1000</message>
There are 5 pre-defined entity references in XML:
< < less than
> > greater than
& & ampersand
' ' apostrophe
" " quotation mark

Referances conti..
◼ Character References: (#)
◼ These contain references, such as A, contains a hash mark (“#”)
followed by a number.
◼ The number always refers to the Unicode code of a character. In this
case, 65 refers to alphabet "A".
◼ EX:
◼ 65#;
◼ THEN OUTPUT IS A

5. Text
◼ The names of XML-elements and XML-attributes are case-sensitive,
which means the name of start and end elements need to be written
in the same case.
◼ To avoid character encoding problems, all XML files should be
saved as Unicode UTF-8 or UTF-16 files.
◼ Whitespace characters like blanks, tabs and line-breaks between
XML-elements and between the XML-attributes will be ignored.
◼ Some characters are reserved by the XML syntax itself. Hence, they
cannot be used directly.

XML DTD and Schema
◼ XML DTD :Document Type Definition.
◼ A DTD defines the structure and the legal elements and attributes of an XML
document..
◼ 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.
◼ There are two types of DTDs:
1) Internal / Embedded DTD.
2) External DTD.

Well Formed XML Documents
An XML document with correct syntax is called "Well Formed".
The syntax rules were described in the previous chapters:
1. XML documents must have a root element
2. XML elements must have a closing tag
3. XML tags are case sensitive
4. XML elements must be properly nested
5. XML attribute values must be quoted.
Example 1:
<?xml version=”1.0”?>
<book>
<title>Java</Title>
<author>James</book>
<pirce>570
</author>
Example 2:
<?xml version=”1.0”?>
<book>
<title>Java</title>
<author>James</author>
<price>500</price>
</book>

Valid XML Documents
◼ A "well formed" XML document is not the same as a "valid" XML document.
◼ A "valid" XML document must be well formed. In addition, it must conform to a document type definition.
◼ The purpose of a DTD is to define the structure of an XML document. It defines the structure with a list of legal
elements.
<!DOCTYPE book
[
<!ELEMENT book
(title,author,price)> <!ELEMENT
title (#PCDATA)> <!ELEMENT author
(#PCDATA)> <!ELEMENT price
(#PCDATA)> ]>
The DTD above is interpreted like this:
• !DOCTYPE book defines that the root element of the document is book
• !ELEMENT book defines that the book element must contain the elements:
• "title, author, price”
• !ELEMENT title defines the title element to be of type "#PCDATA"
• !ELEMENT author defines the author element to be of type "#PCDATA"
• !ELEMENT price defines the price element to be of type "#PCDATA"
• Note: PCDATA: Parse able Character Data, CDATA: Character Data.

Conti..
◼ There are two different document type definitions that can be used with XML:
◼ DTD - The original Document Type Definition
◼ XML Schema - An XML-based alternative to DTD
◼ A document type definition defines the rules and the legal elements and attributes
for an XML document.

1) Internal / Embedded DTD
◼ A DTD can be placed within the XML file or in a separate file. If the DTD is placed
within the XML document, then it is called as internal DTD.
◼ The content inside the square brackets is considered to be the internal subset. And
the keyword! ELEMENT is element declarations, PCDATA is the parsed character
data which are parsed by the XML parsers.
◼ This type of DTD is declared inside the XML Document. It is declared as.
◼ Syntax:
<!DOCTYPE root name [DTD related specification]>
Ex: <!DOCTYPE healthcare [
<!ELEMENT healthcare (#PCDATA)>
]>

PROGRAM FOR INTERNAL DTD
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE students[
<!ELEMENT students (student+)>
<!ELEMENT student (name, branch, section, regdno)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT branch (#PCDATA)>
<!ELEMENT section (#PCDATA)>
<!ELEMENT regdno (#PCDATA)>
<!ATTLIST student id CDATA #REQUIRED>
]>
<students>
<student id="1">
<name>K.Ramesh</name>
<branch>CSE</branch>
<section>A</section>
<regdno>12PA1A0501</regdno>
</student>
</students>

2) External DTD.
◼ This type of DTD is declared outside the XML file with a separate file. External DTD
is used in multiple XML documents, the updation done in this file affects all the XML
document which is quite easy while changing the input file. In external DTD the
‘standalone’ keyword is set to “no”. The external content is specified using a
keyword ‘PUBLIC’ and ‘SYSTEM’. The public keyword is used outside the XML
document followed by a URL (specifies the path).
◼ Note: Multiple DTDs are allowed in which both external and internal DTDs are
combined.
◼ If the DTD is written separately in another file, then it is called as external DTD. An
external DTD is linked with an XML document as shown below:
◼ <!DOCTYPE root-element SYSTEM “filename.dtd”> Markup

PROG FOR EXTERNAL DTD
<!ELEMENT student (id,name,age,addr,email)>
<!ELEMENT id (#PCDATA)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT age (#PCDATA)>
<!ELEMENT addr (#PCDATA)>
<!ELEMENT email (#PCDATA)>
<!DOCTYPE student SYSTEM "student.dtd">
<student> <id>543</id>
<name>Ravi</name>
<age>21</age>
<addr>Guntur</addr>
<email>nsr@gmail.com</email>
</student>
◼ In the above example we are using <!DOCTYPE student SYSTEM "student.dtd">
which is used to provide “student.dtd” code in our “student.xml” file.

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