Introduction to xml

Introduction to XML

Course I: Basics about XML
2003/3/28

Outline
• A first look at XML
• XML Syntax

What is XML?
• Some important facts about XML
– XML stands for the eXtensible Markup Language
– It was developed by W3C
• World Wide Web Consortium
• www.w3.org
– XML 1.0 (2nd Edition)
• W3C recommendation
• http://www.w3.org/TR/REC-xml
– XML 1.1
• Candidate recommendation

Evolution of WWW
• Web was once a publishing
tool for scientific documents
only.
• Now it is a full-fledged medium,
like TV or print.
– Furthermore, Web is an
Interactive medium
– Over 800 million Web pages are
written with HTML

Problems of HTML (I)
• Over the years, HTML has been extended
– HTML has close to 100 tags
– Supporting technologies has been introduced by
vendors
– Still more tags are needed!
• Example
– E-commerce applications need tags for prices, product
references
– Streaming would nee tags to control the flow of media
– HTML is already on the verge of collapsing under its
own weight!!

Problems of HTML (II)
• Some applications would benefit greatly
from a reduction in the tag count!
– More and more people are accessing Web
from PDA and smart phones
• Mobile devices are not as powerful as PC
• The complex Web language cannot be processed
• The web tags are more than the web content itself

Basic Principles of XML
• Increasing specialized applications need more
tags, while other applications want a simple
language
– W3C resolve this dilemma by making two changes to
HTML
• No predefined tags
• Stricter syntax

No Predefined Tags (I)
• XML has no predefined tags.
– The author creates all the tags he needs
• If u need a certain tag, just make it

HTML <table>
<tr>
<td>Price USD 499 </td>
<td><a href=”/newsletter”><b>Pineapplesoft Link</b></a></td>
</tr>
</table>

XML <price currency=“usd”>499.00</price>
<toc xlink:href=”/newsletter”>Pineapplesoft Link</toc>

No Predefined Tags (II)
• How does the browser know what the author-
defined tag looks like?
– Style sheet
• Can we compare different prices?
• What about the current and previous browsers?
• Can we simplify Web site maintenance?

Stricter Syntax
• More than 50% codes in a browser are devoted
to handle errors or sloppiness on the author’s
part.
– Due to increasing using HTML editors
– Browsers are growing in size and becoming slower
• XML adopt a strict syntax for smaller and faster
browsers
<p>Welcome to our site! <img src=logo.jpg>
<p>Welcome to our site! <img src=”logo.jpg”/></p>

Document Structures (I)
• An example
INTERNAL MEMO title
From: Bh Huang
To: Conrad Ho
Regarding: Using User Attention Model in
header
Watermarking

Have u finished the job? Can I adopt the program
directly?I think it will be of great benefits by using
the user attention model.
body

Bh

Document Structures (II)
<?xml version=“1.0”?>
<memo>
<header>
<from>Bh Huang </from>
<to>Conrad Ho</to>
<subject> Using User Attention Model in Watermarking </subject>
</header>

<body>
<para>Have u finished the job? Can I adopt the program directly?I think it will be
great benefits in using the user attention model.</para>
<signature>Bh</signature>
</body>
</memo>

Application of XML
• Most popular applications of XML
– Document applications manipulate information
primarily intended for human consumption
– Data applications manipulate information primarily
intended for software communications

Document Publishing (I)
• XML concentrates on the structure of the
document, making it independent of the delivery
medium

HTML
PDF WML
XML
Document

Document Publishing (II)
• It is possible to edit and maintain documents in
XML and automatically publish them on different
media
– More and more publication are available online and
in print
– Web is changing rapidly
– New markup languages are introduced for specific
devices

Data Applications
• If the structure of a document can be expressed
in XML, so as the structure of a database.
• XML web site can be regarded as a large
database that application can tap

Near-term Applications of XML
• Large web site maintenance
• Exchange information between organizations
• Content made available to different web sites
• E-commerce applications where different
organizations collaborate to server a customer
• Scientific applications with new markup
languages for formulas or specifications
• E-books needs to express rights and ownerships

<?xml version="1.0"?>

<address-book>

An Example <entry>
<name>John Doe</name>
<address>
<street>34 Fountain Square Plaza</street>
John Doe
<region>OH</region>
34 Fountain Square Plaza <postal-code>45202</postal-code>
Cincinnati, OH 45202 <locality>Cincinnati</locality>
US <country>US</country>
</address>
513-744-8889 (preferred)
<tel preferred="true">513-744-8889</tel>
513-744-7098 <tel>513-744-7098</tel>
jdoe@emailaholic.com <email href="mailto:john@emailaholic.com"/>
Jack Smith </entry>
513-744-3465 <entry>
<name>Jack Smith</name>
jsmith@emailaholic.com <tel>513-744-3465</tel>
Never leave messages on his <email href="mailto:jack@emailaholic.com"/>
answering machine. Email instead. <comments>Never leave messages on his answering
machine. <b>Email instead.</b></comments>
Plain text file </entry>
</address-book>
•Which one is easier to read?
•Which one is easier for software to interpret?
XML Document

Elements
• Fundamental Units of XML
– E.g. <tel>513-744-7098</tel>
– Each element is surrounded by a start tag and an
end tag, which are quite similar to HTML
• Start tag is the element name contained in the “<“ and “>”
pair
• End tag must include an additional “/”
– Both a start tag and a end tag is required for an
element

Naming an Element
• The names of elements must follow specific rules.
– The element name must start with letters or _
– Other parts of an element name can consist letters, digits, -, .,
or -.
– Spaces are not allowed in an element name
– Element names are case-sensitive

<copyright-information> <123> <address> address-book
<p> <first name> <ADDRESS> AddressBook
<base64> <Tom&jerry> <Address>
Suggested writing
<decompte.client>
<firstname> Illegal Case sensitivity

Legal

Attributes
• Additional information of elements
– <tel preferred=”true”>513-744-8889</tel>
• An attribute is consisting of its attribute name and value.
• Attribute names must follow the same rules as element names
• Start tag of an element can contain more than one or no
attributes
• Quote marks are required!! (quotes can be ‘ or “)
– <confidentiality level=“I don’t know”>This document is not confidential
</confidentiality>
• Attributes are not parts of element names

Special Attributes
• xml:space
– Specifying the space handling style
• preserve: preserving all spaces
• default: neglecting repeated spaces
• xml:lang
– Specifying content of the element is written in which
language
• <p xml:lang=“en-GB”>What colour is it?</p>
• <p xml:lang=“en-US”>What color is it?</p>

Empty Elements
• Elements having no contents are called empty
elements
– <email href=“bhhuang@ms23.hinet.net” />
– <email href=“bhhuang@ms23.hinet.net”></email>

Hierarchical Structure <?xml version="1.0"?>

<address-book>
of Elements <entry>
Containing texts <name>John Doe</name>
<address>
<street>34 Fountain Square Plaza</street>
<region>OH</region>
<postal-code>45202</postal-code>
<locality>Cincinnati</locality>
<country>US</country>
</address>
<tel preferred="true">513-744-8889</tel>
<tel>513-744-7098</tel>
<email href="mailto:john@emailaholic.com"/>
</entry>
Containing other elements <entry>
<tel>513-744-3465</tel>
<email href="mailto:jack@emailaholic.com"/>
Containing mixture of both <comments>Never leave messages on his answering
machine. <b>Email instead.</b></comments>
</entry>
</address-book>

Hierarchical Structure of Elements (cont.)
<entry> Correct •Elements containing other elements
<name>Jack Smith</name> are called parents
<tel>513-744-3465</tel> •Elements contained in other elements
are called children
<comments>Never leave messages on his answering
machine. <b>Email instead.</b></comments> •Children must be fully contained
</entry> within their parents

<entry>
<tel>513-744-3465</tel>
<comments>Never leave messages on his answering
machine. <b>Email instead. </entry> </comments>
</b>
Wrong

The Root Element
• Each document should have only one root element
– All other elements must be children of the root element
<?xml version="1.0"?> Wrong <?xml version="1.0"?> Correct
<entry> <address-book>
<name>John Doe</name> <entry>
<email href="mailto:john@emailaholic.com"/> <name>John Doe</name>
</entry> <email href="mailto:john@emailaholic.com"/>
<entry> </entry>
<name>Jack Smith</name> <entry>
<email href="mailto:jack@emailaholic.com"/> <name>Jack Smith</name>
</entry> <email href="mailto:jack@emailaholic.com"/>
</entry>
</address-book>

The XML Declaration
• The first line in an XML document is called the XML declaration
– <?xml version="1.0"?>
• As long as a document contains the XML declaration, it means that it is a XML
document
• XML version is included in the XML declaration
• XML declaration is now optional, but is suggested to be included too

•Current version of XML is 1.0.
•The second edition is only the first edition with errors corrected.

Comments
• Comments are surrounded by “”
• Since comments are read by human users only,
the XML parsers will neglect them automatically.
– E.g. 

• Comments cannot be added within an element
– E.g. <name >Jack </name>

Unicode
• Unicode support all languages in the world that
are still being used and mathematical or other
symbols
• All characters in Unicode are represented by 16
bits
– The XML file size will be 2X larger than usual text file
– Solution: specifying “UTF-8” or “UTF-16” in XML declaration
– E.g. <?xml version=“1.0” encoding=“ISO-9959-1” ?>

Entity
• Complicated XML documents are usually located
within several files
• The organizing unit of XML documents is entity
• E.g. if we defined an entity “us” with value
“United States”
– <country>&us;</country>
– <country>United States></country>

Predefined Entities
• < <
Entity reference:
• & &
<company> Marks & Spencer</company>
• > ]]> <company> Marks & Spencer</company>
• ' ‘
• " “ Character reference:
<name> Benoît Marchal</name>

Processing Instruction
• The mechanism to insert non-XML statement
into an XML document
– Compromising the structural property of XML
– Enclosure with “<?” and “>”
– The first word is called target, to which application or
device the instruction is directed
• <?xml version=“1.0” encoding=“ISO-8859-1” ?>
• <?xml-stylesheet href=“simple-ie5.xsl” type=“text/xsl” ?>

CDATA Sections
• Enclosure with
“<![CDATA[“ and “]]>” <? xml version=“1.0”?>
<example>
• XML parser will neglect all <![CDATA[
escaping symbols <?xml version=“1.0”?>
<entry>
• Used when entity <name> John Doe</name>
references are used too </entry>]]>
frequently or another XML </example>
document is included

Common Errors
• The end tag is missing
• XML is case sensitive
• Using spaces in element names
• Quotes of the attribute value is missing

Introduction to xml

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