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					                  Client/Server
                   Computing

                   Byte April 1995
                          &
                 The Martian C/S book




John R Durrett                          1
        Is C/S a passing fad?
       Mainframe          era
            – the “right” hardware vendor
            – software, front-end, apps, etc
       The      PC & C/S revolution
            – “Open systems”
            – mix-and-match
                  c & s platform
                  network protocols

                  DCE infrastructure

                  etc.

       Good:  liberating, low-cost,
        flexibility
       Bad: much harder to manage




John R Durrett                                 2
                        Change

       Old:
            – Servers are scarce
            – LANs
            – Clearly segregated services
       New:
            – Servers are plentiful
            – Proximity does not matter
            – OOUI
                  Integrates   multiple concurrent
                   processes
                  Interaction



John R Durrett                                        3
         Client/Server visions

       The death of mainframes
       Mainframes reborn
       Peace: middle ground
       MIS shops in the new era
            – much harder to manage
            – requires much more variety in
              skills
            – distributing MIS functions to
              users?



John R Durrett                                4
                  What is C/S

       Service     provider & consumer
            – Clients always initiate
            – encapsulation of services
       Shared resources
       Location transparency
            – continual flux
            – global
       Namespace        transparency
            – unique resolution
            – dynamic

John R Durrett                            5
            Network Operating
                System
       Administrative       transparency
            – Synchronization, network
              failures, etc.
       Secured-access       transparency
            – Mutual distrust
            – ID verification
            – Access control lists
       Communications         transparency
            – Heterogeneous data
            – Message oriented middleware


John R Durrett                                6
                 Applications

                electronic mall
       Planetary
       Technologies
            – Rich transaction processing
            – Roaming agents
            – Rich documents




John R Durrett                              7
         Client/Server models

           servers
       File
       SQL databases
            – transaction servers
       TP monitors
       Groupware
       Distributed objects




John R Durrett                      8
                         SQL

       Dominate  today
       Well known language
       Stored procedures
       Extensions
            – triggers
            – rules
       Non-standard       progress
            – LCD is SQL




John R Durrett                        9
                 TP Monitors
       Manage   processes
       Transaction oriented
       Contract
       Fundamental unit
            – recovery
            – consistency
            – concurrency
       Flatmodel
       Sub-transaction model
       Overkill for small LANs
       Scales well to large networks

John R Durrett                          10
                      Groupware

       Multimedia
       Document  management
       Unstructured data
       E-mail
       Work flow processing
            –    sequential routes
            –    parallel routes
            –    feedback
            –    acceptance criteria



John R Durrett                         11
            Distributed Objects

       Encapsulates   data & business
        logic
       Wrappers for legacy apps
       Most standardized
       Interface Definition Language
       Can subsume all other forms of
        C/S




John R Durrett                           12
                  Distribution of
                   applications
       Fat      clients
            – traditional model
            – file server
            – database server
       Fat      servers
            – minimize network load
            – transaction servers
            – object servers




John R Durrett                        13
           C/S Building Blocks
       architecture
            – structural details
            – by computers not plans
            – c/s questions
                   split

                   scalability

                   mobile   - home
       New         demographics
            –    single machine
            –    single server
            –    multi-server
            –    distributed objects

John R Durrett                         14
                   Infrastructure
       client
       server
       middleware
            – transport stacks
                  O/S   interface
            – NOS
                  extends  local O/S
                  single system illusion

                  app coordination

            – ORB
                  services

                  location   transparent connectivity


John R Durrett                                           15

				
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posted:10/9/2012
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