	CS 683 Emerging Technologies Spring Semester, 2003 XML Introduction
	Previous Lecture Notes Index Next © 2003, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 09-Feb-03

Contents of Doc 8, XML Introduction

References
Learning XML , Erik Ray, O'Reilly, 2001

Reading Building Web Services with Java, Graham, Simeonov, et al, pages 33-49, 57-59


Doc 8, XML Introduction Slide # 2

Introduction

XML References
Sun's XML site


http://java.sun.com/xml/
XML Tools - parsers, transformers, SOAP, etc,
Documentation & Tutorials

World Wide Web Consortium (W3C)

http://www.w3.org/
XML specifications, Documentation, Tutorials

XML.com

http://www.xml.com/
XML news, Articles


Doc 8, XML Introduction Slide # 3

History

In the beginning was Guttenberg

But computers changed how to produce

Books
Manuals
Forms
Presentations


Doc 8, XML Introduction Slide # 4

How to represent a document?
Imbed commands or tags in the text

What should the commands do?

Format output

         <bold><center>See the cat run</center></bold>

Structure the document


         <ChapterHeader>See the cat run</ChapterHeader>

Using commands to represent display information makes it clear how the text will look. But one cannot manipulate the structure of the document. Using document structure commands, one can write programs to manipulate the text. One type of manipulation is to display the text on a screen or paper.


Doc 8, XML Introduction Slide # 5

<header>Short History of Tags</header>

GenCode

Late 1960s

Used descriptive content tags (commands)

Generalized Markup Language (GML)

Developed by IBM

Standard Generalized Markup Language (SGML)

1983 ANSI Standard

System for developing tags for documents

Used to create books, manuals, forms, etc

Widely used by IBM, IRS, DOD etc.

Not well known in computer industry


Doc 8, XML Introduction Slide # 6

HTML
Markup language for WWW

Wide spread use

Fixed set of tags

Some tags are presentational

      <CENTER> <B>

Web Browsers permit poorly formed HTML

      <A NAME="WhichOne"></a>
      <b><center>Hello World</b></CENTER><Br>
      <A NAME="WhichOne"></A>

These problems with HTML restrict Web functionality


Doc 8, XML Introduction Slide # 7

XML
XML creators wanted

Flexibility of SGML

Simplicity of HTML

Key differences from HTML

Presentation is separate from document description

Error Checking

Unambiguous Structure


Doc 8, XML Introduction Slide # 8

The Main Point of XML
XML is about

Document structure

Describing data

Sample XML

<?xml version="1.0" ?> 
<CATALOG>
   <CD>
      <TITLE>Empire Burlesque</TITLE> 
      <ARTIST>Bob Dylan</ARTIST> 
      <COUNTRY>USA</COUNTRY> 
      <COMPANY>Columbia</COMPANY> 
      <PRICE>10.90</PRICE> 
      <YEAR>1985</YEAR> 
   </CD>
   <CD>
      <TITLE>Hide your heart</TITLE> 
      <ARTIST>Bonnie Tyler</ARTIST> 
      <COUNTRY>UK</COUNTRY> 
      <COMPANY>CBS Records</COMPANY> 
      <PRICE>9.90</PRICE> 
      <YEAR>1988</YEAR> 
   </CD>
</CATALOG>

From http://194.248.234.174/w3/w3schools/xsl/cd_catalog.xml


Doc 8, XML Introduction Slide # 9

Developing XML
Defining the XML tags

Creating documents using XML tags

Displaying or processing the documents

Creating XML tags requires thinking about

What document structures are important

What data is needed now and later


Doc 8, XML Introduction Slide # 10

Document Structure Example
Which is better?

<Paragraph>
   This is a short paragraph. It will be used as an XML example
</Paragraph>

<Paragraph>
   <Sentence>
   This is a short paragraph. 
   </Sentence>
   <Sentence>
   It will be used as an XML example
   </Sentence>
</Paragraph>

<Paragraph>
   <Author>Roger Whitney</Author>
   <DateCreated>July 20, 2001</DateCreated>
   <Title>XML Example</Title>
   <Sentence>
   This is a short paragraph. 
   </Sentence>
   <Sentence>
   It will be used as an XML example
   </Sentence>
</Paragraph>
Doc 8, XML Introduction Slide # 11

Data Example
Which is better?

   <CD>
      <TITLE>Empire Burlesque</TITLE> 
      <ARTIST>Bob Dylan</ARTIST> 
      <COUNTRY>USA</COUNTRY> 
      <COMPANY>Columbia</COMPANY> 
      <PRICE>10.90</PRICE> 
      <YEAR>1985</YEAR> 
   </CD>

   <CD>
      <TITLE>Empire Burlesque</TITLE> 
      <ARTIST>Bob Dylan</ARTIST> 
      <COUNTRY>USA</COUNTRY> 
      <COMPANY>Columbia</COMPANY> 
      <PRICE>10.90</PRICE> 
      <YEAR>1985</YEAR> 
      < DURATION >89</DURATION>
      <TYPE>Rock</TYPE>
      <TRACKS>12</TRACKS>
      <INSTRUMENT>Guitar</INSTRUMENT>
      <INSTRUMENT>Drum</INSTRUMENT>
      <INSTRUMENT>Banjo</INSTRUMENT>
   </CD>


Doc 8, XML Introduction Slide # 12

The XML Universe

Basic Syntax
XML 1.0 spec, XML 1.1

XLinks

Linking documents together

Namespaces

Namespaces for tags.

XML Markup Languages
XHTML

XML version of HTML

MathML

Used to describe math equations

SMIL

VoiceXML


Doc 8, XML Introduction Slide # 13

The XML UniverseDocument Modeling
Document Type Definitions (DTDs)

Defines legal tags for a document

XML Scheme

Defines data types in XML

Data Addressing & Query
XPath

XPointer

XML Query Language (XQL)

Presentation and Transformation
XML Stylesheet Language (XSL)

XSL Transformation Language (XSLT)

Cascading Style Sheets (CSS)

Extensible Stylesheet Language for Formatting Objects (XSL-FO)


Doc 8, XML Introduction Slide # 14

The XML UniverseParsing, Programming
Document Object Model (DOM)

Simple API for XML (SAX)

XML Information Set

XML Fragment Interchange

Network Protocols
XML-RPC

Simple Object Access Protocol (SOAP)


Doc 8, XML Introduction Slide # 15

XML Syntax

Example

<!-- A simple XML document with comment -->
<greetings>
   Hello World!
</greetings>


Doc 8, XML Introduction Slide # 16

XML Terms

Tag
A piece of text that describes a unit of data

Tags are surrounded by angle brackets (< and >)

Tags are case sensitive

The following are different tags

      <GREETINGS>
      <greetings>
      <Greetings>

Attribute
Qualifier in an XML tag

   <slide title="XML Slide">
   <slide title="Who's on First">
   <name position='First'>

Value of the attribute must be quoted

Can use either single or double quotes


Doc 8, XML Introduction Slide # 17

XML TermsElement
Unit of XML data, delimited by tags

   <greetings>Hello World!</greetings>

   <name>
      <firstName>John</firstName>
      <lastName>Fowler</lastName>
   </name>

Elements can be nested inside other elements

Markup
Tags and comments in an XML document

Content
Anything that is not markup in a document

Document
An XML structure in which one or more elements contains text intermixed with subelements


Doc 8, XML Introduction Slide # 18

XML Document

<greetings>
   <from>
      <nnammee>
         <firstName>Roger</firstName>
         <lastName>Whitney</lastName>
      </nnammee>
   </from>
   <to>
      <name>
         <firstName>John</firstName>
         <lastName>Fowler</lastName>
      </name>
   </to>
   <message>
      How are you?
   </message>
</greetings>

Issues
Is that a typo or a legal tag?

How would we know?


Doc 8, XML Introduction Slide # 19

Levels of XML
Well-formed
XML document that satisfies basic XML structure

Valid
XML document that is well-formed and

Specifies which tags are legal

A Document Type Definition (DTD) is use to specify

Legal tags

Correct tag nesting


Doc 8, XML Introduction Slide # 20

Well-Formed XML Documents

Basic Structure

Optional Prolog
Root Element

<?xml version="1.0" ?> 
<!-- A simple XML document with comment -->
<greetings>
   Hello World!
</greetings>


Doc 8, XML Introduction Slide # 21

Prolog
For well-formed documents the prolog

Is optional
But recommended

Prolog has optional three attributes:

version

Currently 1.0 (1.1 is candidate spec)
- encoding
Character encoding
UTF-8 (default), UTF-16, US-ASCII, etc.
- standalone
Is the complete XML document in one file?

<?xml  version="1.0" encoding='US-ASCII' standalone='yes' ?>

<?xml  version="1.0"  encoding='iso-8859-1' standalone=no ?>


Doc 8, XML Introduction Slide # 22

Comments
Comments can be placed nearly anywhere outside of tags

Comments can not come before <?xml version="1.0" ?>

<?xml version="1.0" ?> 
<!-- Another comment -->
<greetings>
   <from>Roger<!-- Legal comment --></from>
   <to>John</to>
   <message>Hi</message>
</greetings>
<!-- Comments at the end -->


Doc 8, XML Introduction Slide # 23

Root Element
Each XML Document has a single root element

Legal XML Document

<?xml version="1.0" ?> 
<greetings>
   <from>Roger</from>
   <to>John</to>
   <message>Hi</message>
</greetings>

Illegal XML Document

<?xml version="1.0" ?> 
<from>Roger</from>
<to>John</to>
<message>Hi</message>


Doc 8, XML Introduction Slide # 24

XML Document as a Tree

<?xml version="1.0" ?> 
<greetings>
   <from>Roger</from>
   <to>John</to>
   <message>Hi</message>
</greetings>


Doc 8, XML Introduction Slide # 25

Basic Rules for Well-Formed Documents

elements must have start and end tags

Legal	Illegal
<greetings> <from>Roger</from> <to>John</to> <message>Hi</message> </greetings>	<body> <p>Hello world <p>How are you? </body>

elements can use one tag

You can shorten

            <greetings></greetings>

to

            <greetings/>


Doc 8, XML Introduction Slide # 26

Basic Rules For Well-Formed Documents

attribute values must be in quotes

Legal	Illegal
<tag name='sam'>	<tag name=sam>

may not overlap

   <b><center>Bad XML, but ok HTML</b></center>


Doc 8, XML Introduction Slide # 27

White Space
Are the following the same?

   <greetings>
      Hello World!
   </greetings>

   <greetings>Hello World!</greetings>


Doc 8, XML Introduction Slide # 28

White Space
For some applications white space may be important

XML parsers are to pass white space to applications

The application decides if the white space in important


Doc 8, XML Introduction Slide # 29

Special Characters

What happens if we need to use < inside an element?

This is illegal XML

   <paragraph>
      Everyone knows that 5 < 10 & 1 > 0.
   </paragraph>

Need to encode the < and & symbols

   <paragraph>
      Everyone knows that 5 &lt; 10 &amp; 1 > 0.
   </paragraph>

You can used a CDATA section

   <paragraph><![CDATA[
      Everyone know that 5 < 10 & 1 > 0. ]]>
   </paragraph>

Standard element content can not contain: < ]]> &


Doc 8, XML Introduction Slide # 30

Entities

Predefined

Entity	Character
<	<
>	>
&	&
'	'
"	"

XML allows you do define your own entities


Doc 8, XML Introduction Slide # 31

Valid XML Documents

XML document that is well-formed and

Specifies which tags are legal

A Document Type Definition (DTD) is use to specify

Legal tags

Correct tag nesting

Example

<?xml version="1.0" ?>
<!DOCTYPE greetings [
   <!ELEMENT greetings (#PCDATA)>]>
<greetings>
   Hello World!
</greetings>
Doc 8, XML Introduction Slide # 32

Why use DTDs & Valid XML?
Valid XML helps insure the XML is correct

<greetings>
   <from>
      <nnammee>Roger</nnammee>
   </from>
   <to>
      <name>World</name>
   </to>
   <message>
      Hi
   </message>
</greetings>

In the above example humans know that the tag <nnammee> is an error. However, computer programs use XML and how would the program know this is a mistake? If the XML is specified bye a DTD an XML parser would catch the mistake.


Doc 8, XML Introduction Slide # 33

Greetings Example

<?xml version="1.0" ?>
<!DOCTYPE greetings [
   <!ELEMENT    greetings    ( from, to, message, date?)>
   <!ELEMENT    from       ( name )>
   <!ELEMENT    to          ( name )>
   <!ELEMENT    message   ( #PCDATA )>
   <!ELEMENT    date       ( #PCDATA )>
   <!ELEMENT    name       ( #PCDATA )>
]>
<greetings>
   <from>
      <name>Roger</name>
   </from>
   <to>
      <name>World</name>
   </to>
   <message>
      Hi
   </message>
</greetings>


Doc 8, XML Introduction Slide # 34

Greetings Example Explained
Basic DTD structure

      <!DOCTYPE rootElementName [ definitions ]>

<!DOCTYPE greetings [
Makes
"greetings" in the root element 

   <!ELEMENT    greetings    ( from, to, message, date?)>
Defines
"greetings" to contains elements "from", "to", "message" and possible "date"

   <!ELEMENT    from       ( name )>
   <!ELEMENT    to          ( name )>
Defines
"from" and "to" to contain the element "name"

   <!ELEMENT    message   ( #PCDATA )>
   <!ELEMENT    date       ( #PCDATA )>
   <!ELEMENT    name       ( #PCDATA )>
Defines
"message", "date" and "name" to contain text

]>
Ends
the DTD


Doc 8, XML Introduction Slide # 35

What happens here?

<?xml version="1.0" ?>
<!DOCTYPE greetings [
   <!ELEMENT    greetings    ( from, to, message, date?)>
   <!ELEMENT    from       ( name )>
   <!ELEMENT    to          ( name )>
   <!ELEMENT    message   ( #PCDATA )>
   <!ELEMENT    date       ( #PCDATA )>
   <!ELEMENT    name       ( #PCDATA )>
]>
<greetings>
   <from>
      <nnammee>Roger</nnammee>
   </from>
   <to>
      <name>World</name>
   </to>
   <message>
      Hi
   </message>
</greetings>


Doc 8, XML Introduction Slide # 36

Validating and Non-validating Parsers
Validating XML Parsers

Require DTD for the XML
Checks that the XML follows the definitions in the DTD

Non-validating XML Parsers

Checks that the XML is well-formed
Does not use DTD to check for correctness


Doc 8, XML Introduction Slide # 37

DTD Declarations

What can be declared in a DTD?
Elements

Attributes

Entities

Processing Instructions (PI)

Text an XML parser passes to an XML application. The PI is used by the application to further process the XML.

Notations

Notations provide a way of giving the XML parser information on how to handle some piece of data.


Doc 8, XML Introduction Slide # 38

Element Declarations

Empty Element

<!ELEMENT emptyExample EMPTY>

      <emptyExample></emptyExample>

      <emptyExample/>

Element with no restrictions

<!ELEMENT free ALL>

      <free></free>

      <free>Anything goes here</free>

      <free>Some text
         <name>Roger</name>
      <free>


Doc 8, XML Introduction Slide # 39

Element DeclarationsElements containing only character data

<!ELEMENT    name       ( #PCDATA )>

#PCDATA stands for parsed-character data

Entities are expanded in parsed-character data

Elements containing only other elements

<!ELEMENT    greetings    ( from, to, message, date?)>

Elements containing mixed content

<!ELEMENT    sample    ( #PCDATA | name)* >

   <sample>hi</sample>
   <sample>
      <name>Roger</name>
      Some text
      <name>Pete</name>
      <name>Carman</name>
      More Text
   </sample>
Doc 8, XML Introduction Slide # 40

Element Content OperatorsAnd

   <!ELEMENT    andSample    ( A , B)>

"andSample" must contain "A" followed by "B"

Or

   <!ELEMENT    orSample    ( A | B)>

"orSample"

Can contain "A" or "B"
Must contain one of them
Can not contain both


Doc 8, XML Introduction Slide # 41

Element Content OperatorsOptional

   <!ELEMENT    optionalSample    ( A?)>

"optionalSample"

Can contain on "A"
Can be empty

One or more

   <!ELEMENT    onePlusSample    ( A+)>

"onePlusSample"

Must contains one "A"
Can contain any number of "A"s

Any Number

   <!ELEMENT    anyNumberSample    ( A*)>

"anyNumberSample"

Can contain any number of "A"s
Can be empty


Doc 8, XML Introduction Slide # 42

Example

<!ELEMENT article 
   (title, abstract?, author*, (paragraph | table | list )+, reference*)
>

What does this mean?

Must start with a title

Then may be one abstract

Then a list of zero or more authors

Followed by any number of paragraphs, tables and lists

They can be in any order

One of them must occur

At the end there can zero or more references


Doc 8, XML Introduction Slide # 43

Attribute List DeclarationsGeneral Format

<!ATTLIST elementName tagName Type Modifier>

Example

<!DOCTYPE student [ 
   <!ELEMENT    student   ( #PCDATA )>
   <!ATTLIST student 
         name CDATA #REQUIRED
         hometown CDATA "none specified"
         college (arts | agr | law | vet| ilr | engr) #REQUIRED >
]>
<student name='Roger' college='arts'>
   A Good student
</student>

Example Parsed

 
<student name="Roger" college="arts" hometown="none specified">
   A Good student
</student>
Doc 8, XML Introduction Slide # 44

Common Attribute Types
Attribute types determine the type of values an attribute

CDATA
Character data - any sequence of characters

<!ATTLIST student name CDATA #REQUIRED> 
<student name="Roger &amp; Whitney"></student>

NMTOKEN
String of characters starting with a letter
Can contain numbers, letters and some punctuation

<!ATTLIST student name NMTOKEN #REQUIRED> 
<student name="Roger1Whitney"></student>

NMTOKENS
List of tokens

<!ATTLIST student name NMTOKENS #REQUIRED> 
<student name="Roger Whitney"></student>
Doc 8, XML Introduction Slide # 45

Common Attribute Types
Enumerated List
List of all possible values the attribute can have

   <!ATTLIST student 
         college (arts | agr | law | vet| ilr | engr) #REQUIRED >

<student college="arts"></student>


Doc 8, XML Introduction Slide # 46

Attribute Modifiers
#REQUIRED
The attribute must be in the tag

<!ATTLIST student name NMTOKENS #REQUIRED> 
<student name="Roger Whitney"></student>

Default value
The default value of the attribute

<!ATTLIST student hometown CDATA "none specified">
<!ATTLIST student college (arts | agr | law | engr) "engr" >

#IMPLIED
The attribute is optional

<!ATTLIST student hairColor CDATA #IMPLIED>


Doc 8, XML Introduction Slide # 47

Attributes verses Subelements
The following XML documents

Contain the same information
Are both legal

<?xml version="1.0" ?> 
<greetings>
   <from>Roger</from>
   <to>John</to>
   <message>Hi</message>
</greetings>

<?xml version="1.0" ?> 
<greetings from="Roger" to="John" message="Hi"/>

When do we use:

Attributes
Subelements


Doc 8, XML Introduction Slide # 48

Attributes verses SubelementsSome guidelines [1]
Use an element when:

Content is more than a few words long

Order matters

The information is document content

Use an attribute when:

The information modifies how the element is processed

You need to restrict the value

The information is an ID or a reference to an ID


Doc 8, XML Introduction Slide # 49

Entity Declaration
Entities are like macros that are expanded by the parser

<!DOCTYPE roger [ 
   <!ELEMENT    roger   ( #PCDATA )>
   <!ENTITY   address   "1234 Maple Street, San Diego, CA">
]>
<roger>
   He lives at: &address;
</roger>

XML after being parsed

 <roger>
   He lives at: 1234 Maple Street, San Diego, CA
</roger>


Doc 8, XML Introduction Slide # 50

PCDATA Verses CDATA
XML parsers expand entities in PCDATA content

XML parsers do not expand entities that in CDATA

CDATA Example

<!DOCTYPE roger [ 
   <!ELEMENT    roger   ( #PCDATA )>
   <!ENTITY   address   "1234 Maple Street, San Diego, CA">
]>
<roger><![CDATA[
   He lives at: &address;]]>
</roger>

XML after being parsed

 <roger>
   He lives at: &amp;address;
</roger>


Doc 8, XML Introduction Slide # 51

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