CSC340: Tutorial 1 Software Lifecycles

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CSC340 Tutorial 1Software Lifecycles

• TA Yuan An
• Date 900-1000am, Fri. Oct. 3, 2003
• Location BA1130

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In This Tutorial

• The stages in the waterfall life cycle
• About prototyping and incremental life cycles
• The importance of project management
• How users may be involved in a project
• The role of CASE tools in systems development

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The Development Lifecycle

• Starting an information system
• Reasons for development of an information system
• Why does an information system fail?
• Project Lifecycle
• Waterfall life cycle model
• Waterfall life cycle with iteration
• Prototyping
• Evaluation of prototyping

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Starting an Information Systems

• Many reasons for development of information
  systems
• Problem driven competition, crisis
• Change-driven new needs, growth, change in
  business, change in environment
• Opportunity-driven new technology
• Part of previous plan
• .
• But failure does happen.

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Why Does an Information System Fail?

• End users perspective
• No system what system? I havent seen a
  system.
• Unusable
• Insufficient power
• Clients perspective
• Too expensive
• Too late
• Change of mind
• Change of requirements
• Developers perspective
• Wrong requirements
• Insufficient resources
• Incomplete requirements
• Impossible requirements
• Blame the others

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Problems Causing Failures

• Quality problems
• The wrong problem is addressed.
• Wider influence are neglected.
• Analysis is carried out incorrectly.
• Project undertaken for the wrong reasons.
• Process problems
• Requirements drift.
• External events change the environment.
• Implementation is not feasible.
• Poor project management.

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Avoiding the Problems

• We need to adopt strategies and procedures that
  will minimize the occurrence of the problems.
• There is no such thing as a right or a wrong
  strategy or procedure which produces a quality
  system.
• One major source of difficulty is the inherent
  complexity of software development.

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A General Perspective
Building computerized information Systems can be
viewed as a form of problem Solving.
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Problem Solving Model

• Main phases are
• Data gathering
• Problem redefinition
• Finding ideas
• Finding solutions
• Implementation

• These focus on understanding what the problem is
  about

• Concerned with understanding more about the
  nature of the problem and possible solutions

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The Development Life Cycle

• The information systems development process is a
  partially ordered collection of actions, carried
  out by one or more developers, testers, users, or
  other information systems in order to accomplish
  a task.
• The development life cycle is a process by which
  a information system is developed, tested,
  installed and maintained throughout its useful
  history.
• The concept of lifecycle is a useful project
  management tool. A lifecycle consists of phases,
  each of which is a process.

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The Breakdown of Costs

• For large software systems, involving gt10k lines
  of code, the breakdown of costs between different
  phases is as follows
• Requirements Analysis 5
• Design 10
• Programming-in-the-small 15
• Integration 10
• Maintenance and Evolution 60
• Small software systemslt5k LOC
• Specification 10
• Decomposition 20
• Coding 20
• Optimization 15
• Testing 25
• Validation 10
• Systems analysis and design more important.

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What is Described by a Life Cycle?

• The lifecycle describes the temporal, causal and
  I/O relationships between different lifecycle
  phases.
• The lifecycle concept includes the concept of
  feedback (returning to a previous phase) as well
  as moving forward to the next phase.
• In the past, the lifecycle concept was applied to
  the management of complex systems that had some
  sort of physical hardware as their end product,
  e.g., missiles, communication networks,
  spacecraft, etc.

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What Does a Life Cycle Consist of?

• A series steps through which the product
  progresses.
• A life cycle specifies
• The various phases of the process.
• The order in which they are carried out.
• The guidance for project management.
• Next The Waterfall Life Cycle

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The Waterfall Life Cycle Model
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Waterfall Life Cycle

• The traditional life cycle (TLC) for information
  systems development is also known as the
  waterfall life cycle model
• So called because of the difficulty of returning
  to an earlier phase
• The model shown here is one of several more or
  less equivalent alternatives
• Typical deliverables are shown for each phase

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Waterfall Model (cont)

• Consists of a set of phases that a project
  progresses through in a sequential order.
• Each phase must be completed before the project
  can progress to the next phase.
• At the end of each phase is some form of gateway,
  usually a formal review where that decision is
  made.
• There is no overlap between phases.
• Straight forward, simple to understand and use.
• Deliverables are frozen at the end of each phase
  and serve as the baseline for the following
  phases.
• You do not see the software until the end of the
  project (big bang software development).
• Changes are not supposed to happen or are limited
  or are tightly controlled.

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TLC Deliverables

• System Engineering
• High Level Architectural Specification
• Requirements Analysis
• Requirements Specification
• Functional Specification
• Acceptance Test Specifications

Life cycle deliverables (adapted from
Sommerville, 1992).
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TLC Deliverables

• Design
• Software architecture specification
• System test specification
• Design specification
• Sub-system test specification
• Unit test specification

Life cycle deliverables (adapted from
Sommerville, 1992).
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TLC Deliverables

• Construction
• Program code
• Testing
• Unit test report
• Sub-system test report
• System test report
• Acceptance test report
• Completed system

Life cycle deliverables (adapted from
Sommerville, 1992).
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TLC Deliverables

• Installation
• Installed System
• Maintenance
• Change requests
• Change request report

Life cycle deliverables (adapted from
Sommerville, 1992).
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Problems with TLC

• Real projects rarely follow such a simple
  sequential life cycle
• Iterations are almost inevitable
• Time elapses between system engineering and the
  final installation
• The design is unresponsive to business changes
  during the project

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The Waterfall Life Cycle with Iteration
Iteration added to solve some of the problems
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Strengths of TLC

• Tasks in phases may be assigned to specialized
  teams
• Project progress evaluated at the end of each
  phase
• Manage projects with high levels of risks
• Next Prototyping

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PrototypingAdvantages

• Early demonstrations of system functionality help
  identify any misunderstandings between developer
  and client
• Client requirements that have been missed are
  identified
• Difficulties in the interface can be identified
• The feasibility and usefulness of the system can
  be tested, even though, by its very nature, the
  prototype is incomplete

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Prototyping
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PrototypingProblems

• The client may perceive the prototype as part of
  the final system
• The prototype may divert attention from
  functional to solely interface issues
• Prototyping requires significant user involvement
• Managing the prototyping life cycle requires
  careful decision making

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Unified Software Development Process

• Captures many elements of best practice
• Main phases
• Inception is concerned with determining the scope
  and purpose of the project
• Elaboration focuses requirements capture and
  determining the structure of the system
• Construction's main aim is to build the software
  system
• Transition deals with product installation and
  rollout

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User Involvement

• Users can be involved in various ways
• As part of the development team (DSDM)
• Via a consultative approach
• In fact gathering

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Computer Aided Software Engineering

• CASE tools typically provide a range of features
  including
• checks for syntactic correctness
• repository support
• checks for consistency and completeness
• navigation to linked diagrams
• layering
• requirements tracing
• report generation
• system simulation
• performance analysis
• code generation

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The Spiral Life Cycle Model