Distributed Application Services and Ebusiness Part II

1
Distributed Application Services and E-business
Part II
2
So far

• E-business
• Definitions, E-business Models
• E-business Patterns
• Systems requirements
• E-business drivers for Multi-tier Applications
  Architecture
• Emerging web development technologies
• Thin versus Thick Clients, and Thin server vs
  Thick server
• In this session .
• A brief introduction to Java
• Brief introduction to Java
• Overview of XML
• Web applications using Java and XML
• An example web application services
• Tutorial session

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What is Java?

• Java language and environment
• Born on May 23rd 1995.
• Grew out of a product called Oak
• Oak was designed for embedded software and
  consumer devices.
• See http//www.javasoft.com
• Java is an environment is
• Ideal environment for writing object-oriented,
  distributed and platform independent
  applications, real-time, etc.
• Java has a lot in common with C and C
• Versions and editions

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The Java timeline
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How does it work?

• A Java program is compiled into bytecodes
• These bytecodes are interpreted by a JVM
• The JVM converts these instructions into
  appropriate machine code
• The program executes on the machine
• Each platform therefore needs its own JVM
• Enabling WORA -- Write Once, Run Anywhere
• Java Virtual Machine
• An imaginary machine that is implemented by
  emulating it in software on a real machine.
• It specifies Instruction set, register set,
  class file format, stack, garbage collection,
  memory area
• A JVM exists for various operating systems
  including
• Windows 95/98/NT/2000, Solaris, Macintosh, OS/2,
  Linux, OS/400, OS/390, HPUX, AIX, IRIX, EPOC,
  Windows CE, PlamOS, etc.

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Java Runtime Environment
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Running Java Programs

• A Java application is a stand-alone program that
  can use all of the features of the Java language
  environment
• A Java applet is a restricted Java application
  that is designed to be run inside a Java-enabled
  web browser
• Security restrictions
• Applets have a different lifecycle to
  applications
• A Java servlet is the equivalent of an applet,
  which is executed at server-side
• It is a Java application that is designed to be
  run inside a Http servers

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Examples Java Programme

•  / Comments here Example of authenticator
  class /
• package test 
• import java.util.
• import java.security. 
• import com.server.http. 
• public class TestAuthenticator extends
  AbstractAuthenticator
• public void init(CauchoApplication app,
  RegistryNode params)  
• public Principal authenticateCookie(String
  cookieValue) return null  
• public Principal authenticate(String user, String
  password)
• if (password ! null password.equals("quidditc
  h")) return new BasicPrincipal(user)
• else return null  
• public boolean updateCookie(Principal user,
  String cookieValue)
• return true  
• public boolean isUserInRole(Principal user,
  String role)
• return user ! null "user".equals(role) 

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Java 2 Enterprise Edition

• Enterprise JavaBeansTM Architecture
• Defines an API to enable developers to create,
  deploy and manage cross-platform, component-based
  enterprise applications.
• JavaServer PagesTM
• Enables rapid development of server-side
  web-based applications, such as dynamic web
  content management.
• JavaTM Servlet
• Java Naming and Directory InterfaceTM (JNDI)
• JavaTM Message Service (JMS)
• Provides a standard Java API for enterprise
  messaging services such as reliable queuing,
  publish and subscribe communication and various
  aspects of push/pull technologies.
• JavaTM Transaction API (JTA)
• JavaMail

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Example Application 1

• Location Advertisement Services

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But
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Web Page Example
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HTML Code

• lthtml gt
• ltheadgt
• ltmeta name"GENERATOR" content"Microsoft
  FrontPage 4.0"gt
• ltmeta name"Microsoft Theme" content"global 101,
  default"gt
• ltmeta name"Microsoft Border" content"tlrb,
  default"gt
• lttitlegtHome Pagelt/titlegt lt/headgt
• ltbody background"../../_themes/global/glotextb.gi
  f" bgcolor"FFFFCC" text"510000"
  link"999900" vlink"CC9966" alink"990066"gt
• lttable border"0" cellpadding"0" cellspacing"0"
  width"100"gt
• lttrgtlttdgtltfont face"Arial, Helvetica"gt
• ltp align"center"gtltbrgt
• ltfont size"4" face"Arial"gtStudent Learning
  Spacelt/fontgtlt/pgt
• ltp align"center"gtlta href"../Default.htm"gtHomelt/a
  gtnbspnbsp lta href"../cmssem011/Module20speci
  fication.doc"gtModule
• lta href"http//www.cms.livjm.ac.uk/markallen/mult
  i-media.htm"gtTutorialslt/agt lta href"../cmssem011/i
  ndicative_references.htm"gt Reading Listlt/agtlt/pgt
• ltp align"left"gtltfont size"4"gtContemporary
  issues in IT Distributed Applications and
  E-Commerce ltemgtCMSCB3005lt/emgtltfont size"4"
  face"Arial"gtnbsplt/fontgtlt/fontgtlt/pgt
• lt/htmlgt

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Associated XML Code

• lt?xml version"1.0"?gt gt
• lt?xml-stylesheet type"text/xsl"
  href"..\xsl\ENR-change-table.xsl"?gt
• lt!DOCTYPE Components SYSTEM "Project6.dtd"gt
• ltheadgt
• ltmeta name"Microsoft Theme" content"global 101,
  default"gt
• lttitlegt Student Learning Space lt/titlegt lt/headgt
• ltbodygt
• ltmaingt
• ltpage typehtml href"../Default.htm"gt
• ltheadingsgt
• ltheading 1 href"../cmssem011/Module20specifica
  tion.doc"gt
• ltheading 2 href"http//www.cms.livjm.ac.
  uk/markallen/multi-media.htm"gt
• ltheading 3 href"../cmssem011/indicative_referen
  ces.htm"gt
• lt/headingsgt
• lt/maingt
• lt/bodygt
• lt/xmlgt

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What is XML?

• XML is
• an eXtensible Markup Language for describing both
  structured and unstructured information, which
  could be used on the web.
• XML documents containing structured information
  including
• Content words, pictures (vector graphics),
  e-commerce transactions, mathematical equations,
  object meta-data, server APIs, and other XML
  documents.
• XML is a meta-language for defining other markup
  languages not like HTML or SGML
• Unlike Html or SGML it provides
• extensible tag semantics
• a facility to define tags and the structural
  relationships between them.
• All of the semantics of an XML document will
  either be defined by the applications that
  process them or by stylesheets.

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How Is XML Defined?

• XML is defined by a number of related
  specifications
• Extensible Markup Language (XML) 1.0
• Defining the syntax of XML.
• XML Pointer Language (XPointer) and XML Linking
  Language (XLink)
• Defining a standard way to represent links
  between resources. In addition to simple links,
  like HTML's ltAgt tag, XML has mechanisms for links
  between multiple resources and links between
  read-only resources.
• XPointer describes how to address a resource,
• XLink describes how to associate two or more
  resources.
• Extensible Style Language (XSL)
• Defines the standard stylesheet language for XML.
  
• XQL -- Defines a standard query language for XML.
  
• XUL -- Defines a standard user-interface language
  for XML.

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XML Markup 1

• Six kinds of markup used in XML documents
• 1. Elements -- Delimited by angle brackets, most
  elements identify the nature of the content they
  surround.
• It begins with a start-tag, ltelementgt, and ends
  with an end-tag, lt/elementgt.
• Attributes -- Attributes are name-value pairs
  that occur inside start-tags after the element
  name.
• ltdiv class"preface"gtis a div element with the
  attribute class having the value preface.
• 2. entity references -- introduce markup into a
  document, some characters have been reserved to
  identify the start of markup.
• entities are used to represent these special
  characters. Entities are also used to refer to
  often repeated or varying text and to include the
  content of external files.
• Entity references begin with the ampersand and
  end with a semicolon.

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XML Markup 2

• For example, the lt entity inserts a literal lt
  into a document. So the string ltelementgt can be
  represented in an XML document as ltelementgt.
• A special form of entity reference, called a
  character reference, can be used to insert
  arbitrary Unicode characters into your document.
  This is a mechanism for inserting characters that
  cannot be typed directly on your keyboard.
• 3. Comments -- begin with lt!-- and end with --gt.
• Comments can contain any data except the literal
  string.
• 4. processing instructions (PIs) -- are an escape
  hatch to provide information to an application.
• Processing instructions have the form lt?name
  pidata?gt. The name, called the PI target,
  identifies the PI to the application.
• 5. CDATA Sections to instruct the parser to
  ignore most markup characters.
• to prevent xml parser from evaluating a CDATA.
• lt!CDATA p q b (i lt 3) gt 

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XML Markup 3

• Between the start of the section, lt!CDATA and
  the end of the section, gt, all character data
  is passed directly to the application, without
  interpretation.
• The only string that cannot occur in a CDATA
  section is gt.
• 6. Document Type Declarations
• XML allows you to create your own tag names.
• DTD enables document to communicate their
  meta-information to the parser including
• allowed sequence and nesting of tags,
• attribute values and their types
• defaults, the names of external files that may be
  referenced
• formats of some external (non-XML) data that may
  be referenced,
• the entities that may be encountered.

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Validation

• Two categories of XML documents
• Well-formed Documents
• it obeys the syntax and the grammar of XML
  documents.
• A document that includes sequences of markup
  characters that cannot be parsed or are invalid
  cannot be well-formed.
• not well-formed document -- is not XML document.
• well-formed and valid
• well-formed document is valid only if it contains
  a proper document type declaration and if the
  document obeys the constraints of that
  declaration.

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XML Document Parsing
Well-formed
XML
XML Document
Further processing of
Well-formed
Valid
XML
PARSER
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XML Processing and Rendering

• XML Document/DTD/Parser
• Document Object Model (DOM)
• Script/Programming (manipulation of objects)
• XSL (render ready transformation)
• Browser/Display Application
• (rendering)

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Combining Java and XML
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Target System Architecture
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Implementation 1
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Implementation 2
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Implementation 3