System Architecture Design Chapter 10

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System Architecture Design Chapter 10

• Alan Dennis, Barbara Wixom, and David Tegarden
• John Wiley Sons, Inc.
• Slides by Fred Niederman
• Edited by Solomon Negash

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Key Definitions

• The system architecture design consists of plans
  for the hardware, software, communications,
  security , and global support for the new
  application
• The designers must decide if processing will
  occur in the server (server-based), at the
  personal computer (client-based), or in some
  combination of these (client-server based).

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Key Definitions

• The network model shows major components of the
  system, where they are located and how they will
  be connected to one another.
• The hardware and software specifications describe
  these components in detail and aid those
  responsible for purchase and acquisition of these
  products.

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COMPUTING ARCHITECTURES
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Functions of the Application System

• Data storage
• Data access logic
• Application logic
• Presentation logic

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Architectures

• Server based
• Client based
• Client-server based

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Alternative Servers

• In server based architectures, the servers do the
  work and present the results
• Mainframe
• Minicomputer
• Microcomputer (personal computer)

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Server-Based Computing
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Alternative Clients

• In client based architectures, clients do most of
  the work (except data storage) and present the
  results
• Terminals
• Microcomputer (personal computer)
• Special purpose terminals (ATMs,
  kiosks, Palm Pilots, and many
  others)

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Client-Based Computing
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Client-Server-Based Computing (2 Tiers)
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Client-Server Attributes

• Typical Pros
• Compatible with web-based system design
• Scaleable
• Work with multiple vendors/products
• No central point of failure

• Typical Cons/Limits
• Complexity
• New programming languages and techniques (stress
  for personnel)
• More complex to update

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Client-Server -- Three Tiers
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Client-Server -- Four Tiers
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N-Tiered Client-Server Attributes

• Typical Pros
• Separates processing to better balance load
• More scaleable

• Typical Cons/Limits
• Greater load on the network
• More difficult to program and test

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Distributed Objects Computing

• Middleware between clients and servers
• Update middleware when changing client code
• May reduce efficiency of the application
• CORBA
• DCOM

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Realities of Infrastructure Design

• Most often the infrastructure will be in place
• Coordination of infrastructure components is very
  complex
• The application developer will need to coordinate
  with infrastructure specialists

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Selecting a Computing Architecture
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Your Turn

• Consider the course registration system at your
  university
• What computing architecture does it use?
• What computing architecture would you use if you
  were replacing it today?

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INFRASTUCTURE DESIGN
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The Network Model

• No standard format
• Conveys complexity of the system and how
  components fit together
• Components are
• Clients
• Equipment
• Connection to external systems or networks

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Top-Level Network Model
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Hardware and Software Specification

• Used if new hardware or software must be
  purchased
• Actual acquisition of hardware and software
  usually left to a purchasing department --
  especially in larger firms

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Steps in Hardware and Software Specification

• Note hardware in low-level network model to
  create list of needed hardware
• Describe equipment in as much detail as possible
• Consider whether increased processing and traffic
  will absorb unused hardware capacity
• Note all software running on each hardware
  component

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GLOBAL ISSUES
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Global Requirements

• Multilingual requirements
• Concurrent multilingual systems
• Discrete multilingual systems
• Local versus centralized control
• Unstated norms (e.g. dates, currency)
• 24-7 Support
• Communications infrastructure

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SECURITY
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Identifying Threats to the System

• A threat is any potential adverse occurrence that
  can do harm to the application or its data
• Threats come from internal as well as external
  sources
• Categories of threats
• Disruptions, destruction and disaster
• Unauthorized access

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Most Common Threats
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Assessing the Risk of Each Threat
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Creating Controls

• A control is something that mitigates or stops a
  threat
• Controls include
• redundancy
• fault tolerant servers
• disaster recovery plans
• anti-virus software

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Additional Controls Include

• A security policy
• Passwords and encryption
• Firewalls

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Term Project

• What sort of computer architecture would you
  recommend for your project?
• Explain your preference.

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Summary

• The three fundamental computing architectures are
  server-based, client-based, and client-server
  based.
• The network model shows technical components of
  the system and their geographic location
  throughout the organization.
• Hardware and software must be specified for
  acquisition in the project
• The systems analyst needs to also account for
  global issues and security measures.