Frameworks for Component Based Client/Server Computing -Scott M. Lewandowski

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Frameworks for Component Based Client/Server
Computing-Scott M. Lewandowski

• Presented by
• Manish Mehta
• Tulika Rathi
• Sucharita Simhadri
• Anupama Vasanth

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What is in this paper?

• Introduction to Client/Server computing
• Introduction to component technologies -- CORBA
  and DCOM (JavaBeans is not discussed)
• Frameworks for Client/Server computing using
  distributed objects.

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What is Client/Server computing?

• Two logical parts
• -Server that provides service(s).
• -Client that requests services of the server.
• Both client and server together form a
  complete computing system with a distinct
  division of responsibilities.

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Server

• Traditional servers were passive.
• Recent research shows some systems fulfilling the
  theoretical organization of Client/Server in
  which servers can be active.
• Can divide the task in subtasks and delegate each
  subtask to other servers.

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Why is Client/Server so popular?

• Client/Server computing has gained popularity in
  recent years due to proliferation of low-cost
  hardware.
• Monolithic applications fail when the number of
  users accessing a system grows too high or when
  too many features are integrated into a single
  system.

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Client

• Most of the clients have a modern Graphical User
  Interface(GUI)
• GUI is usually provided with the help of
  operating system to maintain consistency across
  multiple applications.(Swing is different)

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Fat v/s Thin -- client/server

• A part of the system with disproportionate(more)
  amount of functionality is FAT.
• A portion of a system with less responsibilities
  delegated to it is THIN.
• FAT Servers
• for example Web Servers
• FAT Clients
• for example Most Database Systems

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N-tier Systems

• The canonical C/S model assumes exactly two
  discrete participants i.e Two-tier system.
• It is also possible to have the application logic
  reside separately from the user interface and
  data, turning the system into N-tier system.
• N-tier system provides more flexibility than
  traditional 2-tier system because of the
  separation of the application logic.
• Decoupling the application logic from the data
  allows data from multiple sources to be used in a
  single transaction.

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Middleware

• To provide transparent access to non-local
  services and resources distributed across the
  network.
• Database Middleware ODBC, SQL, Oracle Glue
• Groupware Middleware Microsoft Exchange, Lotus
  notes
• Internet Middleware HTTP, SSL
• Object-Oriented Middleware CORBA, DCOM

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Functions benefits of c/s system

• Functions
• Regulate access to shared resources when multiple
  clients attempt to access the same resource via
  server.
• Provide a standardized system through which
  network services can be utilized to provide
  location transparent access to all services.
• Benefits
• Natural mapping of applications into a c/s
  framework.(Phone Number)
• Resource intensive applications can be designed
  to run on multiple low-cost systems.

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Distributed Objects and Components

• Classical object v/s Distributed object
• Classical objects are entities that encapsulate
  data and a set of operations(methods) that act on
  that data.
• Classical objects do not exist as separate
  entities once the program is complied.
• Distributed objects can reside any where in the
  network and continue to exist as physical
  standalone entities while remaining accessible by
  other objects.

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Benefits of Distributed objects

• Self-managing distributed objects take
  responsibility for their own resources, work
  across network, and interact with other objects.
• They allow applications to be split up into
  lightweight pieces that can be executed on
  separate machines.
• Distributed objects can generate events to notify
  other objects that an action should take place.
  This synchronization is very useful.
• With middleware, we can ensure interoperation
  between/among objects.

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Components

• Components are the smallest self-managing,
  independent, and useful parts of a system that
  work in multiple environments.
• Components are most often distributed objects
  incorporating advanced self-management features.
• Components may contain multiple distributed or
  local objects, and they are often used to
  centralize and secure an operation.

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New models for c/s computation

• We discuss three models
• Client/server using distributed objects like
  CORBA and DCOM
• Client/server applications using Java
• Client/server applications using Java and CORBA.

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Client/Server with CORBA

• CORBA (Common Object Request Broker Architecture)
• Most important part is ORB
• ORB defines the object model and provides
  bi-directional location-transparent object
  access.
• Internet Inter-ORB Protocol(IIOP) provides
  inter-vendor ORB compatibility by adding several
  CORBA-specific messages to the TCP/IP schema.
• ORB intercepts method invocations form client
  objects and routes them to an appropriate server.

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CORBA (contd.)

• Interface Definition Language (IDL) is used to
  specify the services that an object can provide.
• IDL is defined independent of the factors
  affecting interoperability such as Implementation
  language, tool, Operating System.
• The flexibility is achieved at the expense of
  equipping each client component with an IDL stub
  for each server used.
• CORBA supports Dynamic Method Invocation, handled
  through Dynamic Invocation Interface (DII) .DII
  allows a component to learn about the methods of
  other components at run time.

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CORBA (contd.)

• To accommodate components without IDL-based
  stubs, CORBA provides a Dynamic Skeleton
  Interface (DSI) that binds incoming method calls
  for such objects at run-time.
• Server demands are met via an Object Adapter,
  which provides the core run-time functionality
  required by servers.
• Two ways to locate another object
• Naming Service like while pages in a phone book
• Trade Service like yellow pages (choose from
  pool)

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Client/Server with DCOM

• Primarily uses ActiveX components
• Integration of Java with DCOM is possible through
  Visual J.
• Binding provided with Visual J are strong
  enough so that ActiveXs written in other
  languages can be made to look like remote Java
  objects.
• Uses IDL based on Distributed Computing
  Environment (DCE)-- Not compliant with CORBA.

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Client/Server with DCOM (contd.)

• A request for a reference to a DCOM objects
  results in arbitrary handle.
• DCOM supports a registry of available interfaces.
• For a DCOM client to access the methods of an
  object, it must use a virtual lookup table to
  obtain a pointer to that function.
• Since DCOM objects have no unique object
  identification, there are no naming or trading
  services.

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CORBA v/s DCOM

• DCOM objects do not have a state rather they
  are collections of interfaces.
• The object can be located using Naming or Trading
  services in CORBA. But, in DCOM, a client object
  can not request to be connected to a given
  server.It can only ask to be connected to
  arbitrary server supporting the services needed.
• Benchmarks incorporating network communication
  and simple method invocation show DCOM to be
  almost 20 slower than CORBA.

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CORBA as the Dominant Model

• More portable (Not only Microsoft)
• Open System in the third generation.
• CORBA uses universal security mechanism which is
  independent of platform and OS-level
  security.DCOM uses Windows NT security Model.
• CORBA provides seamless integration for the most
  popular OO languages.DCOM language support is
  limited to Java, C, C and VB.
• CORBA hides the IDL from programmer.
• All industry giants are rallying behind CORBA.

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Java for Client/Server Applications

• Mobile code system provided through bytecodes,
  which solves portability and security problems.
• VM translates the bytecodes into actual machine
  instructions on-the-fly.
• Packages allow dynamic class linking with methods
  that can be overridden at runtime.
• Native support for multi-platform multi-threading
  and thread synchronization.
• Java provides some core frameworks relevant to
  Client/Server computing. (Java Applet, Java
  Beans, Java Security)

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C/S using Java CORBA

• Integration of Java and CORBA can provide a
  platform for universal network computing.
• Advantages of Integration ( by CORBA )
• Superior performance and flexibility.- for
  example HHTP/CGI
• Scalability- load balancing
• Component infrastructure- feature of CORBA
• Split Components- split components in Client and
  Server side components.

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C/S using Java CORBA (contd.)

• Advantages of Integration (by Java)
• Simplified code distribution
• Mobile code
• Agenting
• Superior language feature - Multi-threading

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Frameworks

• Frameworks are tools to help programmers
  construct software systems structures in the same
  way as the analogous real-world system.
• Frameworks provide a way to manage a system of
  interacting objects and to develop objects that
  will integrate seamlessly into the framework.
• The framework is ideally suited for capturing the
  elements common to a family of related systems.
• Frameworks are a valuable tool for ensuring the
  availability of object services.

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Conclusion

• Distributed objects promise to revolutionize the
  stagnant C/S market.
• CORBA, with many advantages over DCOM is
  becoming the Distributed Object standard.
• Leveraging CORBA and Java provides the most
  notable advantages of component technology.

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• Thank you !