Distributed Computing: Comparison of CORBA and Web Services

1
Distributed Computing Comparison of CORBA and
Web Services

• Mentor Dr. Stephan Rupp
• Student Rafat Abusamrah
• Institute of Communication Networks and Computer
  Engineering
• University of Stuttgart

2
Overview

• Introduction
• Distributed computing
• CORBA
• Web Services
• Comparison
• Conclusion

3
Introduction

• An e-business scenario
• A company that receives orders electronically
  from retailers and suppliers, processes orders,
  and provides real time information of the stock
• Retailers can check availability of items in
  stock
• Suppliers can ship goods if the stock is low

4
Introduction

• Solutions?
• Building a website for the company
• - retailers and suppliers would have to check
  the website manually.
• Middleware technology for distributed computing
• - COM/DCOM (Microsoft)
• - Java RMI (SUN)
• - CORBA (OMG)
• - Web Services (W3C)

5
Distributed Computing

• Distributed computing
• Distributed agents over the network that have
  the ability to perform a certain operation in
  parallel according to a context, aiming to solve
  large problems with less computing power
  computers.
• Heterogeneous world
• Different platforms (Mainframes, UNIX
  workstations, PCs with different operating
  systems)
• Different network protocols (TCP/IP, ATM,
  Ethernet,...)
• Different programming languages (C, JAVA,
  PERL,...)

6
Distributed Computing

• To overcome the problem of heterogeneity
• Different kinds of transparencies
• Location transparency
• Access transparency
• Communication transparency
• ..
• How to reference an agent (object) ?

7
Distributed Computing

• The object reference contains
• The network address.
• The port number (transport protocol).
• Object (agent) name or ID.

8
CORBA

• Acronym for Common Object Request Broker
  Architecture, specified by the OMG
• Open and vendor independent architecture and
  infrastructure that computer applications use to
  work together over the network
• ORB (Object Request Broker) mediates the
  communication between applications
• Locating the remote object
• Activating the remote object
• Communicating the client request to the object
• Communicating the reply after carrying out the
  reply

9
CORBA

• IDL (Interface Definition Language)
• Contains the description and types of the methods
• Is programming language independent
• Has its own type system
• Simple example Bank accounts

//IDL module BankSimple   // Define a named type to represent money.   typedef float CashAmount       // Forward declaration of interface Account.   interface Account   interface Bank     ...      interface Account     // The account owner and balance.     readonly attribute string name     readonly attribute CashAmount balance     // Operations available on the account.     void deposit (in CashAmount amount)     void withdraw (in CashAmount amount)   
10
CORBA

• Method invocation
• Dynamic
• Interface Repository (IR)
• Dynamic Invocation Interface (DSI)
• Dynamic Skeleton Interface (DSI)
• Static
• Client stub
• Server skeleton
• Other components and features of CORBA
• Portable Object Adapter, ORB interface, and
  Internet Inter-ORB protocol IIOP

11
CORBA

• Discovery
• Built in services
• Naming service the client is searching for an
  object according to its name
• Trader service the client is searching for an
  object according to certain attributes (features
  and properties)
• If the requested object is found, an object
  reference is returned.

12
CORBA
Example
13
Web Services

• As defined by the W3C A Web service is a
  software system designed to support interoperable
  machine-to-machine interaction over a network. It
  has an interface described in a
  machine-processable format (specifically WSDL).
  Other systems interact with the Web service in a
  manner prescribed by its description using SOAP
  messages, typically conveyed using HTTP with an
  XML serialization in conjunction with other
  web-related standards.

14
Web Services

• Key technologies for Web Services
• XML (eXtensible Markup Language)
• is a markup language for exchanging structured
  messages.
• SOAP
• is a XML based protocol for exchanging messages
  between nodes over different transport protocols
  (HTTP, SMTP, )
• SOAP envelope
• - Header contains information for nodes in the
  message path to its destination
• - Body contains the content used by the
  application

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Web Services

• WSDL (Web Services Description Language)
• Based on XML Schema
• Information
• The interface description (operations, operations
  parameters, data types)
• The implementation description (service location,
  transport protocol)
• An example of a WSDL file

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Web Services

• lt?xml version"1.0" ?gt
• - ltdefinitions name"BNQuoteService"
  targetNamespace"http//www.xmethods.net/sd/BNQuot
  eService.wsdl" xmlnsxsd"http//www.w3.org/2001/X
  MLSchema" xmlnssoap"http//schemas.xmlsoap.org/w
  sdl/soap/" xmlns"http//schemas.xmlsoap.org/wsdl/
  " xmlnstns"http//www.xmethods.net/sd/BNQuoteSer
  vice.wsdl"gt
• - ltmessage name"getPriceRequest"gt
• ltpart name"isbn" type"xsdstring" /gt
• lt/messagegt
• - ltmessage name"getPriceResponse"gt
• ltpart name"return" type"xsdfloat" /gt
• lt/messagegt
• - ltportType name"BNQuotePortType"gt
• - ltoperation name"getPrice"gt
• ltinput message"tnsgetPriceRequest"
  name"getPrice" /gt
• ltoutput message"tnsgetPriceResponse"
  name"getPriceResponse" /gt
• lt/operationgt
• lt/portTypegt

• - ltbinding name"BNQuoteBinding"
  type"tnsBNQuotePortType"gt
• ltsoapbinding style"rpc" transport"http//sche
  mas.xmlsoap.org/soap/http" /gt
• - ltoperation name"getPrice"gt
• ltsoapoperation soapAction"" /gt
• - ltinput name"getPrice"gt
• ltsoapbody use"encoded" namespace"urnxmethods
  -BNPriceCheck" encodingStyle"http//schemas.xmlso
  ap.org/soap/encoding/" /gt
• lt/inputgt
• - ltoutput name"getPriceResponse"gt
• ltsoapbody use"encoded" namespace"urnxmethods
  -BNPriceCheck" encodingStyle"http//schemas.xmlso
  ap.org/soap/encoding/" /gt
• lt/outputgt
• lt/operationgt
• lt/bindinggt
• - ltservice name"BNQuoteService"gt
• ltdocumentationgtReturns price of a book at
  BN.com given an ISBN numberlt/documentationgt
• - ltport name"BNQuotePort" binding"tnsBNQuoteBin
  ding"gt
• ltsoapaddress location"http//services.xmethods
  .net80/soap/servlet/rpcrouter" /gt
• lt/portgt
• lt/servicegt
• lt/definitionsgt

Binding
Data types
Message type
Port type
Port
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Web Services

• Discovery
• UDDI (Universal Description, Discovery and
  Integration)
• Discovery agency that provides find and publish
  services for the requester and provider agents.
• Provides two kinds of information business
  related information and technical information.
• The communication between the UDDI and the
  requester and provider agents uses SOAP messages.

18
Web Services
Scenario
19
Comparison
Aspect CORBA Web Services
Computing model Objects distribution SOAP messages exchanging
Interface definition IDL WSDL
Location transparency Object reference URI
Registry Interface repository UDDI
Service discovery Naming and trader services UDDI
Implementation language Any language with an IDL compiler Any language
Message encoding Binary format Unicode
Transport protocol GIOP/IIOP HTTP, SMTP, HTTPS and other transport protocols
Parameter passing By reference by value By value
State Stateful Stateless
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Conclusion

• The differences between both technologies are due
  to the fact that they were developed for
  different reasons using different technologies.
• Web Services require less effort and cost for
  deployment of the technology components.
• A lot of work has been done to implement SOAP
  messaging over CORBA IIOP.
• WSDL can be generated from CORBA IDL and vice
  versa.
• CORBA and Web Services can play a complementary
  role.

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Questions ??

• Thank you for your attention