Lecture E-Commerce - Chapter 19: eXtensible Markup Language (XML) (part II)

Lecture E-Commerce - Chapter 19: eXtensible Markup Language (XML) (part II). In this chapter students will be able to: XML elements are extensible, XML attributes, XML namespaces, XML encoding, viewing XML files.

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CSC 330 E-Commerce

Teacher

Ahmed Mumtaz Mustehsan

GM-IT CIIT Islamabad

COMSATS Institute of Information Technology

T2-Lecture-4

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eXtensible Markup Language (XML)

Part - II

For Lecture Material/Slides Thanks to: www.w3schools.com

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XML Elements are Extensible

 XML elements can be extended to carry more information.

 Look at the following XML example:

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XML Elements are Extensible…

 Imagine that the author of the XML document added some extra information to it:

 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.

 One of the beauty of XML, is that it can be extended

Message To: Mumtaz From: Tariq Don't forget to attend party on weekend!

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XML Attributes

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<file type="gif">computer.gif</file>

important to the software that wants to manipulate the element:

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XML Attributes Must be Quoted

single or double quotes can be used

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XML Attributes Must be Quoted

can use single quotes

Example:

or you can use character entities:

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XML Elements vs Attributes

Example-1:

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XML Elements vs Attributes…

In Example-1, sex is an attribute

In Example-2, sex is an element

attributes or when to use elements,

However:

Recommendations are:

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XML: Different ways to define information

presented in different ways

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XML: Different ways to define information.

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XML: Different ways to define information.

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Avoid XML Attributes?

Some of the problems with 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)

 Attributes are difficult to read and maintain

Recommendations:

 Use elements for data

 Use attributes for information that is not relevant to the data.

 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 the same way as the id attribute in HTML

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XML Attributes for Metadata…

notes

Recommendations:

Metadata (data about data) should be stored as

attributes, and the data itself should be stored as

elements

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XML Namespaces

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Before we Begin: a review of URI

Uniform Resource Identifier (URI) :

characters which identifies an Internet Resource

Locator (URL) which identifies an Internet domain

address

Resource Name (URN)

In our examples we will only use URLs

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XML Namespaces

This often results in a conflict when trying to mix XML documents from different XML applications

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would be a name conflict Both contain a <table>

element, but the elements have different content and

meaning

A user or an XML application will not know how to

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Solving the Name Conflict Using a Prefix

 Name conflicts in XML can easily be avoided using a name

 In the example above, there will be no conflict because the two

<table> elements have different names But are we allowed to use prefix with a : ?

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XML Namespaces : The xmlns Attribute

When using prefixes in XML

start tag of an element

Example

<h:table xmlns:h="http://www.w3.org/TR/html4/">

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XML Namespaces - The xmlns Attribute

The namespace declaration as an attribute can be defined:

Example-1: each attribute is defined with separate xmsns

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XML Namespaces - The xmlns Attribute…

The namespace declaration as an attribute can be defined:

Example-1: each attribute is defined with combined xmsns defination

The purpose is to give the namespace a unique name However, often

companies use the namespace as a pointer to a web page containing

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Default Namespaces

 Defining a default namespace for an element saves us from using prefixes in all the child elements It has the following syntax:

</table>

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XML Encoding

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XML Encoding

like Norwegian æøå, or French êèé

or save the XML files as UTF-8

for each different character used in a document

called character set, character map, code set, and code page

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of text documents

by a name and a number

Unicode has two variants: UTF-8 and UTF-16

commonly used characters and two (or three) bytes for the rest

and three bytes for the rest

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UTF-8 - The Web Standard

HTML-5, CSS, JavaScript, PHP, SQL, and XML

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 The XML standard states that all XML software must

understand both UTF-8 and UTF-16.

 UTF-8 is the default for documents without encoding

information.

 In addition, most XML software systems understand

encodings like ISO-8859-1 , Windows-1252, and ASCII

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XML Errors

Most often,

three computers, the browser might display

meaningless text, or you might get an error message

Example:

“This XML file does not appear to have any style

information associated with it.”

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When you write an XML document:

standard

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Viewing XML Files

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Viewing XML Files

 Raw XML files can be viewed in all major browsers.

 Don't expect XML files to be displayed as HTML pages.

elements can be clicked to expand or collapse the element

structure To view the raw XML source (without the + and -

signs), select "View Page Source" or "View Source" from the browser menu.

raw XML, you must right click the page and select "View Source"

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Viewing an Invalid XML File

browsers might report the error, some may display

it incorrectly

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Why Does XML Display Like This?

to display the data

XML document, browsers do not know if a tag like

<table> describes an HTML table or a dining table

data, most browsers will just display the XML

document as it is

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The second line links the XML file to the CSS file:

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It is possible to use CSS to format an XML document.

to format an XML document:

The CD catalog formatted with the CSS file

Displaying your XML Files with CSS

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Displaying XML with XSLT

Transformations) is the recommended style sheet language for XML

elements to hide and display, etc

document

XML - XSLT

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XPath is Used in XSLT

 XPath is a syntax for defining parts of an XML document

 XPath uses path expressions to navigate in XML documents

 XPath contains a library of standard functions

 XPath is a major element in XSLT

 XPath is also used in XQuery, XPointer and XLink

XML - Xpath

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XLink is used to create hyperlinks within XML

documents

link

links (for linking multiple resources together)

files

XML - XLink

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XPointer allows the links to point to specific parts of

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The End XML Part-II

T2-Lecture-4 Thank You

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