Lecture 3A: The ClientServer Model

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Lecture 3AThe Client/Server Model

• IT 202Internet Applications
• Based on notes developed by Morgan Benton

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For Today

• Understanding the Client/Server Model

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Fundamental Tasks of Net Apps

• Acquire Data
• Store Data
• Process Data
• Present Datawhich begs the question
• Where is data acquired, stored, processed and
  presented?

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Critical Resources of Net Apps

• Processing Power
• Storage Space
• Bandwidth

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Managing Processing Power

• Processing happens within CPUs
• Its what we refer to when we talk about things
  like Pentium IV, 2.4 GHz
• Were concerned with the execution of
  instructions (e.g. lines of a program)

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Client-side Processing

• Processing should be pushed to the client
  machine
• For apps which require instant responsese.g.
  games, rollover graphics
• In cases where the server handles MANY requests
  simultaneously
• For exchanges which for the most part do NOT
  involve sensitive data
• Client-side scripting handles this

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Server-side Processing

• For more complicated logic
• For handling of sensitive information
• For apps which do not require instantaneous
  feedback (on the order of seconds rather than
  milli- or nanoseconds)
• Application development environments handle this
  processing

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Not an Either/Or Situation

• Applications can successfully balance the
  processing load between the client and server
  working together to provide even faster service
  to the userse.g. LAN games

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Storage Space

• Servers typically have very limited access to
  storage space on client computers
• Servers most often cant afford to keep massive
  amounts of data in main memory
• Hence 3-tier architectures were created with a
  mainframe back end which stores and manages data
  via a DBMS

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3-Tiered Architecture
Application Logic Processing Power
Database DBMS
Data Storage
Security Mechanism
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Bandwidth

• Currently bandwidth is frequently the most
  limiting factor on deploying networked
  applications
• Current speeds
• LAN 100MBps, Gigabit Ethernet
• Corporate Internet/WAN 155MBps OC3, 45MBps, T3
• Home 1.5MBps, Cable/DSL
• Home 56Kbps, dialup

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Bandwidth Limitations

• The amount of data that can be readily
  transferred will dictate what types of
  applications are feasible across a network

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Making Design Decisions

• The nature of the application combined with
  considerations about processing, storage and
  bandwidth will dictate the architecture that is
  eventually chosen and implemented.

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Three methodologies

• Custom Built
• Assembled
• Mix

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The Values of Data

• Asset
• Common Source/Resource
• Interaction
• Decision Tool
• Archival
• Searching or Mining

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Object Oriented Design

• Primarily concerned with the decomposition of
  complex systems into pieces which make intuitive
  sense
• De-coupling of objects makes upgrading pieces of
  a system easier

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Software Object Terms

• Object
• Attribute/Data member
• Method/Procedure
• Interface
• Class
• Instance

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Weakness of OOP/OOD

• The goal is to allow reuse but in practice this
  happens rarely.

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Components and Frameworks

• Software components are reusable by design and
  may be made up of many objects usually assembled
  into full applicationse.g. shopping cart
• Frameworks are full-scale specifications for
  categories of applicationse.g. e-retailerthat
  guide the implementation of those applications in
  specific cases