XML: Technology and Application Lecture 1: Introduction

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XML Technology and ApplicationLecture 1
Introduction

• Jay A. Crossler, Instructor
• Johns Hopkins University

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INTRO to XML

• Unicode Angle Brackets Interoperability

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XML

• eXtensible Markup Language (XML) is a simple,
  standard way to describe text data
• Described as ASCII of the web
• XML - a W3C standard, lets you create your own
  tags
• Tags name the concept you are describing

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Advantages

• More semantics to the data human machine
  readable
• More structures Standard/configurable
  data-types
• Move to the web Plain text files,
  self-referential
• Easy to exchange data with others Web Services
• Platform independent - (relatively) Easy to parse
• Unicode Support AT038T
  

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Example

2HGEJ6675YH519046
Honda 2000
Civic
Kate Winslet 48
My St, Atown, CA
01 18147890
05-11-1974
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HTML vs XML

• HTML tags describe rendering, XML tags describe
  data
• HTML can at most do browser specific presentation
• In HTML Information extraction is not easy
• XML is written for information exchange

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Well-formed Documents

• Tags are nested correctly
• Only one root node
• Well-formed document example
• 1
• 2
• Not well-formed document example
• 12

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XML Syntax

• Elements
• XML tags for markup
• Attributes
• Tuple information of elements
• Declarations
• Instructions to XML processor
• Processing Instructions
• Instructions to external applications

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A Piece of XML

• 
  
• SWISS-PROT
• P09651
• SKSESPKEPEQLRKLFIGGLSFETTDE
  SLRSHFEQWGTLTDCVVMRDPNTKRSRGFGFVTYATVEEVDAAMNARPHK
  VDGRVVEPKRAVSREDSQRPGAHLTVKKIFVGGIKEDTEEHHLRDYFEQY
  GKIEVIEIMTDRGSGKKRGFAFVTFDDHDSVDKIVIQKYHTVNGHNCEVR
  KALSKQEMASASSSQRGRSGSGNFGGGRGGGFGGNDNFGRGGNFSGRGGF
  GGSRGGGGYGGSGDGYNGFGNDGGYGGGGPGYSGGSRGYGSGGQGYGNQG
  SGYGGSGSYDSYNNGGGRGFGGGSGSNFGGGGSYNDFGNYNNQSSNFGPM
  KGGNFGGRSSGPYGGGGQYFAKPRNQGGYGGSSSSSSYGSGRRF

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INTRO to JAVA and Programming

• A quick (p)review

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Java

• Object-oriented programming language.
• Inheritance, overloading and overriding, dynamic
  binding.
• Interfaces, reflection.
• Platform independent.
• Interpreted.
• Lots of APIs.
• Standard utilities.
• 2D and 3D graphics, accessibility, servers,
  collaboration, telephony, speech, animation, and
  more.

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HelloWorld.java

• public class HelloWorld
• public static void main(String args)
• // Display "Hello World!"
• System.out.println("Hello World!")

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Compilation and Execution

• Compile
• Use compiler javac
• Compile java source file to bytecode program
• Execution
• Use interpreter java
• Interprets the bytecode
• Platform independence bytecode program should be
  executable on all platforms

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Object-Oriented Languages

• Object
• An object is a software bundle of related
  variables and methods. Software objects are often
  used to model real-world objects you find in
  everyday life.
• Message
• Software objects interact and communicate with
  each other using messages.
• Class
• A class is a blueprint or prototype that defines
  the variables and the methods common to all
  objects of a certain kind.

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Object-Oriented Languages

• Inheritance
• A class inherits state and behavior from its
  superclass. Inheritance provides a powerful and
  natural mechanism for organizing and structuring
  software programs.
• Interface
• An interface is a contract in the form of a
  collection of method and constant declarations.
  When a class implements an interface, it promises
  to implement all of the methods declared in that
  interface.
• Example Set

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Variables (declared as type name)
public class MaxVariablesDemo public static
void main(String args) // integers
byte largestByte Byte.MAX_VALUE
short largestShort Short.MAX_VALUE int
largestInteger Integer.MAX_VALUE long
largestLong Long.MAX_VALUE // real
numbers float largestFloat
Float.MAX_VALUE double largestDouble
Double.MAX_VALUE // other primitive
types char aChar 'S' boolean
aBoolean true
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Handling Objects
public class Rectangle public int width
0 public int height 0 public Point
origin //Four constructors public
Rectangle() origin new Point(0, 0)
public Rectangle(Point p)
origin p
(continued) public Rectangle(int w, int h)
this(new Point(0, 0), w, h) public
Rectangle(Point p, int w, int h) origin
p width w height h
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Handling Objects
//A method for moving the rectangle public
void move(int x, int y) origin.x x
origin.y y //A method for
computing the area of the rectangle public
int area() return width height

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XML, Part II

• Now it gets interesting

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Example

• cook_time"3 hours"
• Basic bread
• Flouredient
• Yeastingredient
• Warm
  Water
• Saltngredient
• Mix all ingredients together, and
  knead.
• Cover with a cloth, and leave for
  one hour.
• Knead again, place in a tin, bake in
  the oven.

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Example

• Thing
  oneThing two
• Normal
  emphasized strong
  emphasized strong

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XML Technologies we will cover
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DTD XSDs(XML Schema Definitions)

• Describe the structure of valid XML documents
• Use a form of context-free grammar

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XML Syntax

• Elements
• XML tags for markup
• Attributes
• Tuple information of elements
• Declarations
• Instructions to XML processor
• Processing Instructions
• Instructions to external applications

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Elements

• Basic rules
• Start tag and end tag
• Tags must be nested
• Tags may be empty (no enclosed data)
• Whitespace in element content usually ignored

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Attributes

• Provides additional information about an element
• Enclosed by quotes - either " or '
• Case-sensitive
• May be character data or tokenized
• value"Blue Peter" (character data)
• value "blue" (single token)
• value "red green blue" (tokens)
• Values may be enumerated or defaulted (DTD)

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Comment Declaration

• Comments are not considered part of XML document
  and should not be published
• Cannot have additional '--' in comment
• Cannot embed inside other declarations

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Processing Instructions

• Information required by an external application
• Processing Instructions
• Format -
• XML PI -
• Confusingly, this is called the XML declaration,
  but is a processing instruction

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Entities

• XML document may be distributed among a number of
  files
• Each unit of information is called an entity
• Each entity has a name to identify it
• Defined using an entity declaration
• Used by calling an entity reference

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An XML DTD

• name CDATA IMPLIED
• length CDATA IMPLIED
• REQUIRED

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Attribute Types

• CDATA
• Character data
• NMTOKEN
• Single token
• NMTOKENS
• Multiple tokens
• ENTITY
• Attribute is entity ref
• ENTITIES
• Multiple entity ref's

• ID
• Unique ID
• IDREF
• Match to ID
• IDREFS
• Match to multiple ID's
• NOTATION
• Describe non-XML data
• Name group
• Restricted list

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Attribute Types

• CDATA
• name "Tom Jones"
• NMTOKEN
• color"red"
• NMTOKENS
• values"12 15 34"
• ENTITY
• photo"MyPic"
• ENTITIES
• photos"pic1 pic2"

• ID
• ID "P09567"
• IDREF
• IDREF"P09567"
• IDREFS
• IDREFS"A01 A02"
• NOTATION
• FORMAT"TeX"
• Name group
• coord"X"

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Character Data Declaration

• For occasions when text must contain
  uninterpreted markup characters
• Press ltltltENTERgtgtgt
• But, why is this in your data? This should be
  stylistic information!

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XML Schema

• hema
• targetNamespacehttp//localhost8080/crossler
  
• xmlnshttp//localhost8080/crossler
• elementFormDefault"qualified"
• type"xsdstring"/
• type"xsdinteger"/
• Whats wrong with this XML?

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Formatting

• Cascading Style Sheets
• href"myStyleSheet.css"?
• Extensible Style Sheets Language
  Transformations
• href"transform.xsl"?

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Why XML Schema(why not just DTD)?

• More data types
• Complex data types
• More like a database schema
• Will continue in Lecture 2 Format
• Time to assign the first Project!