Enterprise Computing

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Enterprise Computing
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Possible Client Server Solutions

• CGI (Common Gateway Interface)
• Active Server Pages
• 2 Tier Java
• 3 Tier Java
• Sockets
• JavaIDL / CORBA
• JavaRMI

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CGI

• Code (PERL, REXX, C, C) run by webserver in
  response to client request code creates a web
  page HTML in real time and returns to client
• Old Technology pre- HTTP
• reliable
• resource hog

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CGI (more)

• Very useful used in conjunction with Java based
  clients for things like
• Report Generation
• Data retrieval
• Persistant object storage
• Could be replaced by server side Java servletts
• Hard to maintain program state

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CGI (more)
Static Web with forms tags ltform
action/CGI-BIN/AAA.PRLgt
Browser
Web Server
CGI Program
DB
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CGI (more)

• If another user requests a CGI while the CGI is
  already running the web server spawns a thread
  and runs another instance of the CGI there.
• For frequently run CGIs many copies may be in the
  machine at the same time
• resource hog

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CGI (more)
Browser
Browser
Browser
Web Server
DB
CGI Program
CGI Program
CGI Program
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Active Server Pages

• HTML pages
• Embedded scripting language and proprietary
  server support are used to make forms objects
  appear to be database aware
• Main contenders
• Netscape One
• Microsoft Active Server Pages
• Cold Fusion

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Netscape One

• Core Technologies
• HTML
• Java JavaScript
• Java Runtime Interface (JRI)
• Netscape Suite Spot Server
• Netscape Internet Foundation Classes (Java)
• Netscape Live Connect
• Netscape Live Wire
• CORBA / ORB Technology

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Netscape One (More)

• Live Connect
• Enables communication between JavaScript and Java
  applets
• Live Wire
• Enables web site management
• Provides database connectivity between Netscape
  browser, HTML, JavaScript
• special HTML-like tags

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Netscape One (more)
HTML
Netscape Web Server
JavaScript
Java
LiveWire
LiveConnect
LiveWire
DB
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Microsoft Active Server Pages

• Core technologies
• MS Internet Information Server
• MS Internet Explorer (IE4.0)
• VBScript
• Java
• ActiveX
• SQL Server Access
• DCOM

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Microsoft Active Server Pages

• Works only on Windows

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Microsoft Active Server Pages
HTML
IIS
JavaScript VBScript
VBScript
Java
ActiveX
IE 4.0
DB
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Cold Fusion

• Core Technologies
• Proprietary Scripting language
• Java
• Proprietary Cold Fusion Server (must run on same
  machine as the Webserver (any web server)

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2-Tier Client Server

• Java based Client application or applet
• JDBC
• Database

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2-Tier Client-Server - application
Java Client Application using JDBC APIs
JDBC Enabled Database
TCP/IP
This application architecture is simple but wont
scale to very many users
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2-Tier Client-Server - applet
Unix or Windows
Browser
HTML
Webserver
applet
JDBC Enabled DB
V 1.1 JVM
Webserver and DB must be on same IP address
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2-Tier Problems

• Client has to do everything
• DBs arent meant to handle large numbers of
  simultaneous invocations
• Good only for infrequently used apps

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3-Tier Client-Server

• Java based Client application or applet
• Server/middleware
• Database

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3-Tier Client Server
Sockets JavaIDL JavaRMI
JDBC Native
Client
Client
Server
DB
Client
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3-Tier Advantages

• Server can manage database connections
  efficiently
• Client can focus on business logic
• Server can preformat data for client
• Running server on high performance hardware can
  improve client perceived performance

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JavaIDL

• In Java we cannot separate a classs definition
  from its implementations we can in C
• Header files
• Implementation files
• CORBA allows the separation of definition and
  implementation

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JavaIDL

• CORBA uses IDL for defining interfaces, language
  specific IDL compilers are available
• create target language skeletons and stubs to be
  used by developers for building CORBA clients and
  servers
• CORBA objects talk to each other via interfaces

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CORBA Object Communications
IIOP
Object A
Object B
Interface
Interface
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Conceptually ...
Client
Server
Client
Server
ORB
Client
Server
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Really though...
Registration
ORB
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Client
Server
Services
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Client
Server
3
Client
Server
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What happens...

• Server objects register their methods with the
  orb naming service
• Client binds to the orb naming server for a
  server object method
• Naming service return location of server object
  and disconnects
• Client connects to server at returned location

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This is very simplified

• Very
• The local ORB expert is Steve Woods and is
  currently working on an Orb based IRAD project

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Orb Info

• The Visigenics VisiBroker Orb is built into
  Netscape Communicator 4.0
• Borland just bought Visigenics
• Borlands and Visigenics vision is a CORBA based
  world
• Why didnt Microsoft buy Visigenics?

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Why MS didnt buyVisigenics

• Wrong vision
• MS Vision is DCOM not CORBA

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Remote Method Invocation

• Similar to C RPCs
• Instead of creating and instantiating an object
  on your machine create it on another machine and
  communicate with it as if it were a local object
• eliminates CORBA overhead
• comes with JDK 1.1

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RMI

• RMI classes let you generate stubs and skeleton
  layers like JavaIDL
• Remote reference Layer translates stup and
  skeletion calls to native transport calls on the
  host architecture and carries out remote
  reference protocols

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RMI Model
Client
Server
Stubs
Skeletons
Remote
Remote
Reference
Reference
Transport
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RMI

• Currently RMI uses its own on the wire protocol
• Sun has committed to make the on the wire
  protocol IIOP