Chapter 09B

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Chapter 09B Powered By Docstoc
					Systems Analysis & Design
7th Edition

 Chapter 9
Chapter Objectives

  Provide a checklist of issues to consider when
   selecting a system architecture
  Describe servers, server-based processing,
   clients, and client-based processing
  Explain client/server architecture, including
   tiers, cost-benefit issues, and performance
  Compare in-house e-commerce development to
   packaged solutions

Chapter Objectives

  Explain the difference between online and
   batch processing
  Define network topology, and provide
   examples of hierarchical, star, bus, and ring
   network models
  Describe wireless network standards,
   advantages, and disadvantages

Chapter Objectives

  Explain network protocols and licensing
  Explain performance measurement, fault
   management, backup, and disaster recovery
  Describe the systems design specification


  An effective system combines elements into
   an architecture, or design, that is flexible,
   cost-effective, technically sound, and able to
   support the information needs of the
  System architecture translates the logical
   design of an information system into a
   physical structure that includes hardware,
   software, network support, and processing
System Architecture Checklist

  The analyst must consider seven specific issues
   that will affect the architecture choice
    – Enterprise resource planning (ERP)
    – Initial and total cost of ownership (TCO)
    – Scalability
    – Web integration
    – Legacy system interface requirements
    – Processing options
    – System security
System Architecture Checklist

  Enterprise Resource Planning (ERP)
   – The objective of ERP is to establish a
     company-wide strategy for using IT
   – Advantage: it describes a specific hardware
     and software environment ( platform) that
     ensure connectivity and easy integration of
     future system including in house software
     and commercial packages
   – Supply chain management
System Architecture Checklist

  Initial Cost and TCO
    – Ask questions like the following
        • If in-house development was selected as the best
          alternative initially, is it still the best choice?
        • If a specific package was chosen initially, is it
          still the best choice?
    – Answers might affect the initial cost and
      TCO for the proposed system

System Architecture Checklist

  Scalability
    – Scalability, also called extensibility, refers to
      a system’s ability to expand, change or
      downsize easily to meet the changing need
      of a business enterprise
    – Especially important in implementing
      systems that are volume-rated, such as
      transaction processing systems

System Architecture Checklist
 Web Integration
  – An information system includes applications
  – Web-centric architecture that follows internet
    design protocols and enables a company to
    integrate the new application into its e-
    commerce strategy.
  – Avoids many of the connectivity and
    compatibility problems that typically arise
  – IBM uses E-marketplaces to describe internet
    based solutions that allow seller and buyers to
    automate procurement process and achieve 10
    substantial benefits
System Architecture Checklist

  Legacy System Interface Requirements
   – The new system might have to interface with
     one or more legacy systems
   – Interfacing a new system with legacy systems
     involves analysis of data formats and
   – The analyst must know if the new application
     eventually will replace the legacy system

System Architecture Checklist

  Processing Options
    – In planning the architecture, designers also
      must consider how the system will process
      data - online or in batches
    – Provision must be made for backup and
      speedy recovery in the event of system

System Architecture Checklist

  Security Issues
    – Security is a concern at every stage of
      system development
    – Web-based systems introduce additional
      security concerns

Planning the Architecture

  Every information system involves three
   main functions:
   – Data storage and access methods
   – Application programs to handle the
     processing logic
   – An interface that allow users to interact with
   – Depending on the architecture the three
     function are performed on a server, on a
     client, or are divided between the server and
     the client.                                 14
Planning the Architecture

  Servers
    – Server is a computer that supplies data,
      processing services, or other support to one
      or more computers called client
    – The term mainframe architecture typically
      describes a multiuser environment where the
      server is significantly more powerful than
      the clients

Planning the Architecture
  – Server-based processing
     • In a centralized design, the remote user’s keystrokes
       are transmitted to the mainframe, which responds by
       sending screen output back
     • Today mainframe architecture used in credit card
       company or in bank.

Planning the Architecture
  Clients
   – Stand-Alone Computing
       • Stand-alone computing was inefficient and
       • Maintaining data on individual workstations
         raised major concerns about data security,
         integrity, and consistency
       • It was impossible to protect and back up valuable
         business data, and companies were exposed to
         enormous risks
       • This led to data inconsistency and unreliability

Planning the Architecture

    – Local and wide area networks
       • Most of the companies resolved the problems of
         stand alone computing by joining clients into local
         area network that allows sharing of data and
         hardware recourses.
       • A wide area network (WAN) spans long distances
         and can connect LANs that are continents apart
       • The network is transparent
       • Compared to mainframe architecture, distributed
         systems increase concerns about data security and
Planning the Architecture

  Clients
   – Client-based processing

Client/Server Architecture

  Overview
   – Client/server architecture refers to system that
     divide processing between one or more
     networked clients and a central server.
   – In typical client/server system, the client
     handles the entire user interface, including data
     entry, data query, and screen presentation logic.
   – The server stores the data and provides data
     access and database management functions.

Client/Server Architecture

  Overview
   – The early client/server system was expensive.
       • Few clear standards exist
       • client needed powerful hardware and software to
         handle shared processing tasks.
       • Many companies had an installed base of mainframe
         data, called legacy data, which was difficult to access
         and transport to a client/server environment
    – The client/server concept continues to expand
      to include clients and servers outside the
Client/Server Architecture
 Client/Server Design Styles
  – Depends on the style the processing is divided
    between the server and the clients
  – The nature of communication is depends on
    the type of the server
      • A database server process individual SQL
      • The transaction server handles a set of SQL
      • An object server exchanges object messages with
      • A web server sends and receives Internet based 23
Client/Server Architecture
   • A web server sends and receives Internet based

Client/Server Architecture
   Types of Clients: Fat and Thin
    – A fat client also called a thick client
      design locates all or most of the
      application processing logic at client.
    – A thin client design locates all or most
      of the processing logic at the server.
    – The table in next slide describes the
      characteristics of the fat and thin

Client/Server Architecture
  Types of Clients: Fat and Thin

Client/Server Architecture

  Client/Server Tiers
   – Two-tier designs
       • The user interface resides on the client, all data
         resides on the server, and the application logic can
         run either on the server or on the client or be
         divided between the client and server.
    – Three-tier design – n-tier designs
       • The user interface runs on the client and the data
         stored on the server, a middle layer process the
         client requests and translates them into data access
         commands that can be understood and carried out
         by the server                                   27
Client/Server Architecture

  Client/Server Tiers
   – Three-tier design – n-tier designs
        • Think of the middle layer as an application server,
          because it provides the application logic, or
          business logic
        • The middle layer is more efficient and cost-
          effective in large-scale systems

Client/Server Architecture

  Middleware
   – Enables the tiers to communicate and pass
     data back and forth
   – Provides a transparent interface that enables
     system designers to integrate dissimilar
     software and hardware
   – Can integrate legacy systems and Web-based

Client/Server Architecture
  Cost-Benefit Issues
   – Client/server systems enable the firm to scale
     the system in a rapidly changing environment
   – Client/server computing also allows
     companies to transfer applications from
     expensive mainframes to less expensive client
   – Client/server systems reduce network load and
     improve response times

Client/Server Architecture
  Client/Server Performance Issues
   – In contrast to the centralized system, a
      client/server design separates applications and
   – Client/server systems must be designed so the
      client contacts the server only when necessary

Client/Server Architecture
  Client/Server Performance Issues
   – Another issue is the data storage. Data can
      be stored in in more than one location using
      Distributed database management system
      (DDBMS) . DDBMS has the following
        • Data stored closer to users can reduce network
        • The system is scalable, so new data sites can be
          added without reworking the system design
        • The system is less likely to experience
          catastrophic failure
Client/Server Architecture
  Client/Server Performance Issues
   – DDBMS has also the following
       • It can be more difficult to maintain controls and
         standards when data is stored in various locations
       • The architecture of DDBMS is more complex
         and difficult to manage.

Internet-Based Architecture

  Developing E-Commerce Solutions In-House

Internet-Based Architecture

  Packaged Solutions and E-commerce Service
    – Many vendors offer ready to use systems for
    – Another alternative is to use an application
      service provider (ASP)
    – Must consider whether the advantage of lower
      initial cost outweighs the disadvantage of
      reduced flexibility later on

Internet-Based Architecture

  Corporate Portals
   – A corporate portal
     can provide access
     for customers,
     employees, suppliers,
     and the public
       • Oracle and SAP offer
         powerful enterprise
         portal software

Processing Methods
  Online Processing
   – Online systems handles transactions when
      and where they occur and provide output
      directly to users
   – Example can be an airline reservation
      system and ATM system.

Processing Methods

Processing Methods
  Online Processing
   – Online processing systems have four
      typical characteristics:
       1. The system processes transactions completely
          when and where they occur
       2. Users interact directly with the information
       3. Users can access data randomly
       4. The information system must be available
          whenever necessary to support business

Processing Methods

  Batch Processing
   – In a batch processing system, data is collected
     and processed in groups, or batches
   – The IT operations group can run batch
     programs on a predetermined schedule without
     user involvement; and Batch programs require
     significantly fewer network resources than
     online systems

Processing Methods

  Combined Online and Batch Processing
   – Online processing offers an inherent
     advantage because data is entered and
     validated as it occurs
   – Online processing is more expensive
   – Backup and recovery for online processing is
     more difficult
   – In many situations, batch processing is cost-
     effective, less vulnerable to system
     disruption, and less intrusive
Processing Methods

  Combined Online and Batch Processing
   – An example can be the Point of Sale (POS)

Network Models
  A network allows the sharing of hardware,
   software, and data resources in order to reduce
   expenses and provide more capability to users.
  When planning a network design, you must
   consider network terms and concepts, including
   the OSI model, network model tools, network
   topology, network protocol, licensing issues,
   and wireless network.

Network Models
 The OSI Reference Model
  – The Open System Interconnection (OSI)
    model which describes how data actually
    moves from an application on one computer
    to an application on another network,
    consists of seven layers
      • Network layer: defines network addresses and
        determines how data is routed over the network
      • Data link layer: defines specific methods of
        transmitting data over the physical layer, such as
        defining the start and end of a data block
      • Physical layer: contains physical components
        that carry data, such as cabling and connecters 44
Network Models
  – Each layer performs specific function, as

 Network Topology
  – Ring network:
     • Resembles a circle of
       computers that
       communicate with each
     • Data flows in only one
     • One disadvantage is if a
       device fails, the devices
       downstream from the
       failed device cannot
       communicate with network
 Network Topology
  – Hierarchical network:
      • One or more powerful
        servers control the network
      • An example is retail chain,
        with central computer that
        stores data about sales
        activity and inventory
        levels and local computer
        handle store level

 Network Topology
  – Bus network:
     • A single communication path
       connects the network server,
       departmental server,
       workstations, and peripheral
     • An advantage is that devices
       can be attached or detached
       from the network at any point
       without disturbing the rest of
       the network.
     • Disadvantage is that the performance can decline as
       more devices added                                  48
 Network Topology
  – Star network:
     • Has a central computer
       with network devices
       connected to it
     • At the center of the star
       which is called hub, a
       central server manages the
     • Disadvantage is that the
       entire network is depend
       on the central computer.

Network Models

  Network Protocols and Licensing Issues
   – The network must use a protocol
   – A popular network protocol is Transmission
     Control Protocol/Internet Protocol (TCP/IP)
   – A familiar example of a TCP/IP protocol is
     the file transfer protocol (FTP)

Network Models

  Wireless Networks
   – A wireless local area network, or WLAN
   – Uses 802.11 protocol that is developed by
     Institute of Electrical and Electronics
     Engineers (IEEE)
   – This standard referred to Wi-Fi which stands
     for wireless fidelity
   – Although they have many advantages, wireless
     networks pose special concerns with regard to
     system security
 Wireless Networks
  – Bluetooth is another wireless communication
    that is very popular for short distance wireless
  – On addition to 802.11 protocols for LANs,
    IEEE is working on 802.16 standards which is
    communication protocol for MANs
    (metropolitan area networks) these
    specification that IEEE calls Wireless MAN™
    - WiMAX are expected to enable wireless
    multimedia applications with a range of up to
    30 miles
System Management and Support
  Performance Management
    – Performance management tools are designed to
      collect information about system resources and
      activity levels
    – Firms such as NetScout Systems offer
      comprehensive performance management
    – The NetScout Web site mentions studies that
      show network delays cost the industry more
      revenue than actual stoppages

System Management and Support

  Fault Management, Backup, and Disaster
    – Fault management
       • Includes monitoring the system for signs of
         trouble, logging all system failures, diagnosing
         the problem, and applying corrective action

System Management and Support
  Fault Management, Backup, and Disaster
    – Backup and disaster recovery
       •   Backup
       •   Recovery
       •   Disaster recovery plan
       •   Backup and recovery planning depends on the
           type of system involved

System Management and Support

  Fault Management, Backup, and Disaster
    – Backup and disaster recovery
       • Another common strategy is to use a RAID
         (redundant array of independent disks) system
       • RAID systems are called fault-tolerant because
         the failure of any disk does not disable the
       • Experienced IT professionals often note that the
         three most important system security tools are
         backup, backup, and more backup
Systems Design Completion
 System Design Specification
  – A typical system design specification uses a
      structure similar to the following:
       1. Executive summary (brief over view of the job)
       2. System components (design of input/output,
          data, and network)
       3. System environment (constrains, or conditions,
          affecting the system)
       4. Implementation requirements (start up process,
          initial data entry, training requirement and
          software test)
       5. Time and cost estimates
       6. Appendices provide supplemental material 57
Systems Design Completion
  User Approval
   – Users must review and approve the interface
     design, report and menu designs, data entry
     screens, source documents, and other areas of
     the system that affect them
   – When the system design specification is
     complete, you distribute the document to a
     target group of users, IT department personnel,
     and company management

Systems Design Completion
  Presentations
    – The presentations give you an opportunity to
      explain the system, answer questions, consider
      comments, and secure final approval
    – The first presentation is to the systems analysts,
      programmers, and technical support staff
    – Your next presentation is to department
      managers and users from departments affected
      by the system

Systems Design Completion
  Presentations
    – The final presentation is for company
    – Key objective: to obtain management’s
      approval and support for the next development
    – Management might reach one of three
      decisions: proceed with systems development,
      perform additional work on the systems design
      phase, or terminate the project

Chapter Summary
  An information system combines hardware,
   software, data, procedures, and people into a
   system architecture
  The analyst must consider enterprise resource
   planning, initial cost and TCO, scalability, Web
   integration, legacy interface requirements,
   security, and processing options
  System security is an important concern
  An architecture requires servers and clients

Chapter Summary

  Compared to file server designs, client/server
   systems are more scalable and flexible
  In implementing a design, an analyst should
   consider e-commerce strategies, the availability
   of packaged solutions, and corporate portals,
   which are entrances to a multifunction Web
  The primary processing methods are online
   and batch processing

Chapter Summary

  Networks allow the sharing of hardware,
   software, and data resources in order to reduce
   expenses and provide more capability to users
  The way a network is configured is called the
   network topology
  The system design specification presents the
   complete systems design for an information

  Chapter 9 complete

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