Web Technology - XML

7/30/2019 Web Technology - XML

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EXtensible Markup

Language(XML)

U. K. Roy


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An HTML system

HTML

documentWeb Server

Web Client

Internet

Parser,

formatter,

interface


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Role of HTML

HTML Designed to display data

Focuses on appearance

Has a fixed set of predefined tags

Ambiguity


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Role of XML

EXtensible Markup Language W3C recommendation, 1998

Designed to structure, transport and store data

Transformation and Dynamic datacustomization

Interoperable way to represent and process

documents (not necessarily on web)

Self descriptive


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Example

John

Ani

Reminder

Return my book on Monday


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Another Example

RequiemMozart

Equivalent HTML code:

Requiem is a song composed byMozart


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Role of XML

Not a replacement of HTML XML focuses on what data are

HTML focuses on how data look

Tags are custom defined (not predefined)

Functional meaning depends on application

Everything must be marked up correctly


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XML and Databases

XML brings benefits of DBs to documents Schema to model information directly

Formal validation, locking, versioning, rollback...

But

Not all traditional database concepts map

cleanly, because documents are fundamentally

different in some ways


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XML Building blocks

Element Delimited by angular brackets

Identifies the nature of the content it surrounds

General format:

Empty element:

Attribute

Name-value pairs that occur inside start-tags afterelement name, like:


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XML Building blocks--Prolog

The part of an XML document that precedes theXML data

Includes

A declaration: version [, encoding, standalone]

An optional DTD (Document Type Definition )

Processing Instructions (Optional)


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XML Elements

XML Elements are Extensible

More and more elements may be added to carry moreinformation

XML Elements have Relationships

Elements are related as parents and children

Elements have Content

Elements can have different types of content: empty content

simple content

element content mixed content

attributes

XML elements must follow the naming rules


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XML Elements naming rules

Names can only contain letters, digits and some

other special characters.

Names can not start with a number or punctuation

marks

Names must not contain the string xml, XML orXml

Names can not contain while space(s).


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Anatomy of an element

Use a hyphen: .

Start-tag Content End-tag

Element

Elementtype

Attribute

name

Attribute

value

(character)

entity

reference Elementtype

Attribute


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The Basic Rules

XML is case sensitive

This is incorrect

This is correct


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The Basic Rules

All start tags must have end tagsMozart

Mozart

Empty Element


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The Basic Rules

Elements must be properly nested

This is incorrect nesting

This is correct nesting


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The Basic Rules

XML declaration must be the first statement


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The Basic Rules

Every document must contain a root element

.....


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The Basic Rules

Attribute values must be quoted with invertedcommas

Ani

John


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The Basic Rules

Certain characters are reserved for parsing

if salary< 1000 then

if salary < 1000 then


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Predefined entities

< < less than

> > greater than

& & &ampersand

' ' apostrophe

" " quotation mark


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The Basic Rules

With XML, white space is preserved

With XML, a new line is always stored as LF

Comments in XML:

Can go almost anywhere (not inside tags) Schemas can contain comments, too


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Common Errors for Element Naming

Do not use white space when creating names

for elements

Element names cannot begin with a digit,

although names can contain digits

Only certain punctuation allowed periods,

colons, and hyphens


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XML Attributes

Located in the start tag of elements Provide additional information about

elements

Often provide information that is not apart of data

Must be enclosed in quotes

Should I use an element or an attribute? metadata (data about data) should be stored as attributes,

and that data itself should be stored as elements


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Types of XML Documents

XML document

Well Formed XML.

Syntax is correct

Valid XML.

Well formed Validated against a DTD/Schema


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Well-Formed XML

Properties

Documents must have a root element

Elements must have a closing tag

Elements must be properly nested

Attribute values must be quoted

Advantage

Avoids fixed nature like HTML

Flexible

Expandable


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Valid XML

Properties

Well Formed

Comply with the rules defined in a DTD/Schema

Advantage

Clear Understanding

Data verification

Interoperability

Better document processing


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XML Validation

XML

schema

XML

Parser

XML

document

Error

messages

Optimized

XML

document

xmllint --valid sample.xml


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Dislaying XML

Sanchoita

Rabindranath Tagore

2009

200.00


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Document Type Definition

Allows developers to create a set of rules to

specify legal content and place restrictions on

an XML file

Parser generates error, if XML document does

not follow the rules contained within DTD

Including a DTD

Using internal declaration

Using external file Both


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Internal (standalone) DTD

For custom documents

Uses DOCTYPE declaration

]>

Hello, world!

Specify in XML declaration


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External DTD

Most common

Use DOCTYPE declaration before root element

Hello, world!


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External plus Internal DTD

Usually to declare entities

Use DOCTYPE declaration before root element

Hello, world&excl;


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DTD XML Building Blocks

XML documents consist of following blocks

Elements

Attributes

Entities

< > & " &apos

PCDATA

Parsed CharacterDATA

Entities will be expanded

CDATA

CharacterDATA

Entities will not be expanded


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Declaring Elements

An empty element

Example

Usage:


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Declaring Elements

Element with data

Example


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Declaring Elements

Usage:

U. K. Roy

What is the full form of DTD?

[email protected]

This is an XML document


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DTD Declarations

Example : Elements with Data

Valid Usage

April

This is a month

Invalid Usage:

cant have children!-->JanMarch


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Declaring Elements

Element with Children (sequential)

Example

body)>


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Declaring Elements

Inner elements must also be declared


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Declaring Elements

Usage:

[email protected]

[email protected]

Learn DTD from

www.w3schools.com


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Declaring Elements

Usage:

S. C. Mallick Road

Kolkata

700032


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Using internal DTD

]>

[email protected]

[email protected] DTD from w3schools.com


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DTD Declarations

John Doe1234 Preston Ave.

Charlottesville, Va22903


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Declaring Elements

Occurrence Indicators

Term Meaning Example

, Sequence Operators a, b, c

| Choice operators a | b | c

+ One or more a+

* Zero or more a*

? Single optional a?

() grouping (a)


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Examples


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Declaring Elements

Example

Publisher?)>


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Cautions concerning DTDs

All element declarations begin with

The ELEMENT declaration is case sensitive

Elements declared with the #PCDATA content

model can not have children

When describing sequences, the XML

document must contain exactly those elements

in exactly that order.


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Declaring Attributes

General Syntax

Example

10


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The attribute-type can be one of the following:Type DescriptionCDATA The value is character data(en1|en2|..) The value must be one from an enumerated listID The value is a unique idIDREF The value is the id of another elementIDREFS The value is a list of other idsNMTOKEN The value is a valid XML nameNMTOKENS The value is a list of valid XML namesENTITY The value is an entityENTITIES The value is a list of entitiesNOTATION The value is a name of a notationxml: The value is a predefined xml value


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The default-value can be one of the following:Value Explanationvalue The default value of the attribute#REQUIRED The attribute is required#IMPLIED The attribute is not required#FIXED value The attribute value is fixed


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Examples

id ID #REQUIRED

name CDATA #IMPLIED>

type (bullets|ordered|glossary) "ordered">


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Examples

Valid XML:

E l #REQUIRED


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Examples--#REQUIRED

DTD:

Valid XML:

Invalid XML:

E l #IMPLIED


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Examples--#IMPLIED

DTD:

Valid XML:

valid XML:

E l #FIXED


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Examples--#FIXED

DTD:

Valid XML:

Invalid XML:

E l E t d


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Examples--Enumerated

DTD:

XML example: or

El t f Att ib t ?


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Elements of Attributes?

attributes cannot contain multiple values (child

elements can)

attributes are not easily expandable (for future

changes)

attributes cannot describe structures (childelements can)

attributes are more difficult to manipulate by

program code

attribute values are not easy to test against a DTD

D l i E titi


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Declaring Entities

General Syntax

Example // //

&language; is standardized by &W3C;&copyright; UKR

Displaying XML


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Displaying XML

XHTML

XML namespace

XML DOM

XPath

XSL (XSLT+XPath)

Client side

By browser

Explicitly by author (using JavaScript)

Server side

Schema

Displaying XML


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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 i t HTML


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XML into HTML

XSLT can transform into (called "output

method"):

XML

HTML

text

Server-side XSLT engine

content in XML

served as HTML browser never knows

Cli t id XSL


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Client-side XSL

XML

XSLT

FO

Server side XSL


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Server-side XSL

XML

XSLT

XSLTengine HTML

XML DOM


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XML DOM

Everyday ItalianGiada De Laurentiis200530.00

Harry PotterJ K. Rowling200529.99

Learning XMLErik T. Ray200339.95

XML DOM Tree


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XML DOM Tree


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Questions?