understanding xml by kamalakar dandu

8/2/2019 Understanding XML by Kamalakar Dandu

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Understanding XML


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Introduction to XML

What Is XML?

XML is a text-based markup language that

is fast becoming the standard for datainterchange on the Web. As with HTML,

you identify data using tags (identifiers

enclosed in angle brackets, like this: ).

Collectively, the tags are known as"markup".


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Why Is XML Important?

Data Identification XML tells you what kind of data you have, not how to

display it. Stylability

When display is important, the stylesheet standard, XSL,lets you dictate how to portray the data. Inline Reusability One of the nicer aspects of XML documents is that they

can be composed from separate entities.

Linkability Thanks to HTML, the ability to define links between

documents is now regarded as a necessity.


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Why Is XML Important? (Contd..)

Easily Processed As mentioned earlier, regular and consistent notation

makes it easier to build a program to process XML data. Hierarchical

Finally, XML documents benefit from their hierarchicalstructure. Hierarchical document structures are, ingeneral, faster to access because you can drill down tothe part you need, like stepping through a table ofcontents

Plain Text Since XML is not a binary format, you can create and editfiles with anything from a standard text editor to a visualdevelopment environment


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Why Is XML Important? (Contd..)

exchange data in a platform independent way.

share data between programs without prior

coordination.

W3C standardized API. Based on Universal character set.

web language specks xml


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differences between XML & HTML

data presentation

parser impl.

predefined tags


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XML Vocabularies

Scientific vocabularies (CML) business vocabularies (EDI) Legal vocabularies (Extensible form description

language)

medical vocabularies (HL7) computer vocabularies channel definition format (CDF) structured graph format (SGF) Bean markup language (BML) open s/w description (OSD) xml metadata interchange (XMI) call policy markup language


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Here is an example of some XML data

you might use for a messaging

application:

[email protected]

[email protected] Is Really Cool

How many ways is XML cool? Let me

count the ways...


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Tags and Attributes

Tags can also contain attributes

How many ways is XML cool? Let mecount the ways...


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Empty Tags

One really big difference between XML and HTML is thatan XML document is always constrained to be wellformed.

Sometimes, though, it makes sense to have a tag thatstands by itself. For example, you might want to add a"flag" tag that marks message as important.

How many ways is XML cool? Let me count theways...


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Comments in XML Files

XML comments look just like HTML comments:

How many ways is XML cool? Let me count

the ways...


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The XML Prolog


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Processing Instructions

An XML file can also containprocessing

instructions that give commands or

information to an application that is

processing the XML data. Processinginstructions have the following format:


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How Can You Use XML?

Traditional data processing, where XML encodes thedata for a program to process

Document-driven programming, where XML documentsare containers that build interfaces and applications from

existing components Archiving--the foundation for document-driven

programming, where the customized version of acomponent is saved (archived) so it can be used later

Binding, where the DTD or schema that defines an XMLdata structure is used to automatically generate asignificant portion of the application that will eventuallyprocess that data


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Basic Standards

SAX Simple API for XML

DOM

Document Object Model

DTD Document Type Definition

Namespaces

The namespace standard lets you write an XML

document that uses two or more sets of XML tags XSL

Extensible Stylesheet Language

XSLT (+XPATH)

Extensible Stylesheet Language for Transformations


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Schema Standards

A DTD makes it possible to validate the structure ofrelatively simple XML documents, but that's as far as itgoes.

DTD

XML

Validation


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Document Type Definition

(DTD)

Data sent along with a DTD is known as validXML.

In this case, an XML parser could check incoming

data against the rules defined in the DTD to make

sure the data was structured correctly.

Data sent without a DTD is known as well-

formed XML.

Here an XML-based document instance, such as thehierarchically structured weather data shown, can be

used to implicitly describe itself.


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DTD for our Simple XML A DTD consists of a left square bracket character ([)

followed by a series of markup declarations, followed by a

right square bracket character (]).

]>

This is the most simplest XML document


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DTC Declarations

Element type declarations

Attribute-list declarations

Entity declarations

Notation declarations Processing declarations

Comments

Parameter entity references


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Element Type

Contentspec>

Title permitted ti have only char data

You can use any key word which is legal under General Root tag

Element must be empty. It can not have anything

Book element must have the 3 elements in the same order

OtherSkills*)

Qualification could be one or more, XMLExpousure is optionaland OtherSkills could be zero or more


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Element Type (Contd)

order operator meaning

, strict sequence

| choiceTable 2-2 DTD Element Qualifiers

Qualifier Name Meaning

? Question Mark Optional (zero or one)

* Asterisk Zero or more

+

Plus Sign One or more


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A Simple Example


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]

>

Devotional Songs by PankajKajal by Pankaj

Classical Songs by Pankaj


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Attribute List

In a valid XML document you must also explicitly declare

all attributes that you might intend to use with the

documents elements.

You define this by using a type of DTD markup known as

an attribute-list declaration.

This declaration does the following

Defines the names of the attributes associated with

that element

Specifies the data type of each attribute

Specifies for each attribute whether that attribute is

required.


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Attribute List (Contd)

Attibute-list declaration has the following

form:

Name - is the type name of the element

associated with the attribute

AttDefs - is the attribute definition thatdefines one atribute


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Attribute List (Contd)

attribute default:

#REQUIRED

#IMPLIED

#FIXED

Attribute type CDATA ID IDREF

IDREFS NOTATIONS

(IDREF)


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eg.(IDREF)

Ramesh Clerk 12-4-1999 7000/- 300/- 10

Mohan Manager 12-4-1997

12000/-


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NOTATION Example DTD

#REQUIRED>


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NOTATION Example XML

//xml

1

]

>

Hum Aapke Hain Kaun

Love Story

Madhuri Dixit


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Using an External DTD

The XML File MyExternDTD.XML

Hum Aapke Hain Kaun

Love Story

Madhuri Dixit


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Using an External DTD (Contd..)

Document Definition file - MyExternDTD.dtd


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entity

predefined entities

character entityref

< >

& &

' '" "


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general entities

DTD Syntax

XML Usage

&ent-name;


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external entities


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parameter entity

"age CDATA #IMPLIED

weight CDATA #IMPLIED

height CDATA #REQUIRED

>

using parameter entity

CDATA #REQUIRED>


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parameter entity (Contd)

Example :


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parameter entity (Contd)

//xml

1

]]>

#REQUIRED> ]]>


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conditional section (Contd)

#REQUIRED>

]]>

]]>


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Exercises - ????

DTD for Visiting Card - Is it OK?

Group+, Address) >

]>

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