The System Life Cycle

Week 14

LBSC 690

Information Technology

Agenda

• Questions

• Systems analysis

• Building complex systems

• Managing complex systems

• Final exam review

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?

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

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?

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)

Some Library Activities

• Acquisition

• Cataloging

• Reference– Online Public Access Catalog (OPAC)

• Circulation

• Weeding

• Reserve, recall, fines, interlibrary loan, …

• Budget, facilities schedules, payroll, ...

Discussion Point:Integrated Library System

• What functions should be integrated?

• What are the key data flows?

• Which of those should be automated?

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

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

The Waterfall Model

Requirements

Specification

Software

Test Plan

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, …)

The Spiral Model

1.0

0.5

2.0

3.0

1.1

1.2

2.1

2.2

2.3

Some Unpleasant Realities

• The waterfall model doesn’t work well– Requirements usually incomplete or incorrect

• The spiral model is expensive– Redesign leads to recoding and retesting

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

Rapid Prototyping + Waterfall

UpdateRequirements

ChooseFunctionality

BuildPrototype

InitialRequirements

WriteSpecification

CreateSoftware

WriteTest Plan

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

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

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

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

Discussion Points:Managing Complex Systems

• Critical system availability– Why can’t we live without these systems?

• Understandability– Why can’t we predict what systems will do?

• Nature of bugs– Why can’t we get rid of them?

• Auditability– How can we learn to do better in the future?

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

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

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

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 Bentley’s

The Grand Plan

Networks

XML

Multimedia

Computers

Interaction

Search

Communication

Web

Life Cycle

PolicyDatabases

Programming

Web Databases

Midterm

Project

Final

Quiz

Computer Systems

• Hardware – Types of hardware– Storage hierarchy– Moore’s law

• Software– Types of software– Types of interfaces

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

Structured Documents

My Browser

• The Web– HTTP, HTML, URL

• XML

Multimedia• Compression, compression, compression

– Image: lossy vs loseless– Video: frames are alike– Speech: voice predictable– Music: masking

• Streaming

Media Sever

Internet

Buffer

Human-Computer Interaction

• Human-machine synergy

• Mental models

• Input and output devices

• Interaction styles– Direct manipulation, menu, language based

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

Databases• Structured information

– Field->record->table->database

– Primary key

• Normalized tables (relations)– Remove redundancy, inconsistency, error

– Easy update, search

• Join links tables together– Through foreign key

• Access provides visual operations

Web-Database Integration

• Access “Data Access Pages”

• PHP

• SQL

Computer-Mediated Communication

• Synchronous / Asynchronous

• Remote / local

• One-to-one / many-to-many

• Computer-Supported Cooperative Work

The Web

• Huge, dynamic, redundant, and diverse

• Multimedia, multilingual, multicultural

• Deep Web

• Internet Archive

Search

• Exact match

• Term-based ranked retrieval

• Recommender systems

• Web search– Links and anchor text

• Evaluation

Policy• Ownership

– Equitable access

– Controlled access

• Identity– Choosing good passwords

• Privacy– Government / commercial

• Integrity

Life Cycle

• Systems analysis

• Software development models

• Managing complex systems

R.J. Bentley’s Filling Station

Thursday Dec 15, 2005 at 8:30 P.M.