The System Life Cycle - PowerPoint PPT Presentation

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The System Life Cycle

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Same question styles as the midterm. Some may require use of the computer ... Music: masking. Streaming. Media Sever. Internet. Buffer. Human-Computer Interaction ... – PowerPoint PPT presentation

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Title: The System Life Cycle


1
The System Life Cycle
  • Week 14
  • LBSC 690
  • Information Technology

2
Agenda
  • Questions
  • Systems analysis
  • Building complex systems
  • Managing complex systems
  • Final exam review

3
The System Life Cycle
  • Systems analysis
  • How do we know what kind of system to build?
  • User-centered design
  • How do we discern and satisfy user needs?
  • Implementation
  • How do we build it?
  • Management
  • How do we use it?

4
Systems Analysis
  • First steps
  • Understand the task
  • Limitations of existing approaches
  • Understand the environment
  • Structure of the industry, feasibility study
  • Then identify the information flows
  • e.g., Serials use impacts cancellation policy
  • Only then can you design a solution

5
Analyze the Information Flows
  • Where does information originate?
  • Might come from multiple sources
  • Feedback loops may have no identifiable source
  • Which parts should be automated?
  • Some things are easier to do without computers
  • Which automated parts should be integrated?
  • What other systems are involved?
  • And what information do they contain?

6
Analyzing Information Flows
  • Process Modeling
  • Structured analysis and design
  • Entity-relationship diagrams
  • Data-flow diagrams
  • Object Modeling
  • Object-oriented analysis and design
  • Unified Modeling Language (UML)

7
Some Library Activities
  • Acquisition
  • Cataloging
  • Reference
  • Online Public Access Catalog (OPAC)
  • Circulation
  • Weeding
  • Reserve, recall, fines, interlibrary loan,
  • Budget, facilities schedules, payroll, ...

8
Discussion PointIntegrated Library System
  • What functions should be integrated?
  • What are the key data flows?
  • Which of those should be automated?

9
User-Centered Design
  • Start with user needs
  • Who are the present and future users?
  • How can you understand their needs?
  • Evaluate available technology
  • Off-the-shelf solutions
  • Custom-developed applications
  • Implement something
  • Evaluate it with real users

10
The Waterfall Model
  • Key insight invest in the design stage
  • An hour of design can save a week of debugging!
  • The motivation behind DoD Standard 2167
  • Requirements
  • Specifies what the software is supposed to do
  • Specification
  • Specifies the design of the software
  • Test plan
  • Specifies how you will know that it did it

11
The Waterfall Model
Requirements
Specification
Software
Test Plan
12
The Spiral Model
  • Build what you think you need
  • Perhaps using the waterfall model
  • Get a few users to help you debug it
  • First an alpha release, then a beta release
  • Release it as a product (version 1.0)
  • Make small changes as needed (1.1, 1.2, .)
  • Save big changes for a major new release
  • Often based on a total redesign (2.0, 3.0, )

13
The Spiral Model
2.3
1.2
0.5
1.1
2.2
1.0
2.1
2.0
3.0
14
Some Unpleasant Realities
  • The waterfall model doesnt work well
  • Requirements usually incomplete or incorrect
  • The spiral model is expensive
  • Redesign leads to recoding and retesting

15
The Rapid Prototyping Model
  • Goal explore requirements
  • Without building the complete product
  • Start with part of the functionality
  • That will (hopefully) yield significant insight
  • Build a prototype
  • Focus on core functionality, not in efficiency
  • Use the prototype to refine the requirements
  • Repeat the process, expanding functionality

16
Rapid Prototyping Waterfall
Update Requirements
Write Specification
Choose Functionality
Initial Requirements
Create Software
Build Prototype
Write Test Plan
17
Implementation Requirements
  • Availability
  • Mean Time Between Failures (MTBF)
  • Mean Time To Repair (MTTR)
  • Capacity
  • Number of users for each application
  • Response time
  • Flexibility
  • Upgrade path

18
Alternative Architectures
  • Batch processing (e.g., recall notices)
  • Save it up and do it all at once
  • Timesharing (e.g., OPAC)
  • Everyone uses the same machine
  • Client-Server (e.g., Web)
  • Some functions done centrally, others locally
  • Peer-to-Peer (e.g., Kazaa)
  • All data and computation is distributed

19
Management Issues
  • Retrospective conversion
  • Even converting electronic information is
    expensive
  • Management information
  • Peak capacity evaluation, audit trails, etc.
  • Sometimes costs more to collect than it is worth!
  • Training
  • Staff, end-users
  • Privacy

20
Hands On What Goes Wrong?
  • Check out Risks Digest for a random date
  • http//catless.ncl.ac.uk/Risks
  • Pick a random date near your birthday
  • Find a case of unexpected consequences
  • Try to articulate the root cause
  • Not the direct cause

21
Discussion PointsManaging Complex Systems
  • Critical system availability
  • Why cant we live without these systems?
  • Understandability
  • Why cant we predict what systems will do?
  • Nature of bugs
  • Why cant we get rid of them?
  • Auditability
  • How can we learn to do better in the future?

22
Critical Infrastructure Protection
  • Telecommunications
  • Banking and finance
  • Energy
  • Transportation
  • Emergency services
  • Food and agriculture
  • Water
  • Public health
  • Postal and shipping
  • Defense industrial base
  • Chemical industry and hazardous materials

SCADA Supervisory Control and Data Acquisition
23
National Cyberspace Strategy
  • Response system
  • Analysis, warning, response, recovery
  • Threat and vulnerability reduction
  • Awareness and training program
  • Return on investment, best practices
  • Securing government systems
  • International cooperation

24
Summary
  • Systems analysis
  • Required for complex multi-person tasks
  • User-centered design
  • Multiple stakeholders complicate the process
  • Implementation
  • Architecture, open standards,
  • Management
  • Typically the biggest cost driver

25
Talk to Me About the Exam!
  • About 5 questions
  • Same question styles as the midterm
  • Some may require use of the computer
  • Comprehensive - covers the entire course
  • Emphasis and structure from the second half
  • Two hours
  • Post-exam discussion at Bentleys

26
The Grand Plan
Interaction
Quiz
Midterm
27
Computer Systems
  • Hardware
  • Types of hardware
  • Storage hierarchy
  • Moores law
  • Software
  • Types of software
  • Types of interfaces

28
Networks
  • Types of Networks
  • LAN, WAN, Internet, Wireless
  • Packet Switching
  • Ethernet, routers, routing tables
  • Layered Architecture and protocols
  • TCP/UDP
  • IP address/domain name
  • Encryption

29
Structured Documents
  • The Web
  • HTTP, HTML, URL
  • XML

My Browser
30
Multimedia
  • Compression, compression, compression
  • Image lossy vs loseless
  • Video frames are alike
  • Speech voice predictable
  • Music masking
  • Streaming

Media Sever
Buffer
Internet
31
Human-Computer Interaction
  • Human-machine synergy
  • Mental models
  • Input and output devices
  • Interaction styles
  • Direct manipulation, menu, language based

32
Programming
  • Programming languages
  • Machines require low-level specific instructions
  • Humans require high-level abstraction
  • Can create any behavior from 3 control structures
  • Sequential execution
  • Conditional
  • Iteration
  • Javascript interpreters are in Web browsers

33
Databases
  • Structured information
  • Field-gtrecord-gttable-gtdatabase
  • Primary key
  • Normalized tables (relations)
  • Remove redundancy, inconsistency, error
  • Easy update, search
  • Join links tables together
  • Through foreign key
  • Access provides visual operations

34
Web-Database Integration
  • Access Data Access Pages
  • PHP
  • SQL

35
Computer-Mediated Communication
  • Synchronous / Asynchronous
  • Remote / local
  • One-to-one / many-to-many
  • Computer-Supported Cooperative Work

36
The Web
  • Huge, dynamic, redundant, and diverse
  • Multimedia, multilingual, multicultural
  • Deep Web
  • Internet Archive

37
Search
  • Exact match
  • Term-based ranked retrieval
  • Recommender systems
  • Web search
  • Links and anchor text
  • Evaluation

38
Policy
  • Ownership
  • Equitable access
  • Controlled access
  • Identity
  • Choosing good passwords
  • Privacy
  • Government / commercial
  • Integrity

39
Life Cycle
  • Systems analysis
  • Software development models
  • Managing complex systems

40
R.J. Bentleys Filling Station
Thursday Dec 15, 2005 at 830 P.M.
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