7/30/2019 20100317 Clark Spiral

1/24

SPEAKER :KAI-JIA CHANG

ADVISER :QUINCY WU

DATA :2010-03-17

Spiral Model

7/30/2019 20100317 Clark Spiral

2/24

Outline

2

Introduction

The spiral model

EvaluationConclusions

References

7/30/2019 20100317 Clark Spiral

3/24

Introduction

3

A Risk-Driven Approach

Different idea of software development.

How does this project affect the developers and the

clients?How does each step in the project affect its overall

development?

Not used in previous development models.

Usually code-driven or document-driven.

7/30/2019 20100317 Clark Spiral

4/24

Introduction

4

Background on software process models

1950Code-and-fix model

1956 Stagewise model (Bengington )

1970Waterfall model (Royce)1971 Incremental model(Mills)

1977 Prototyping model(Bally and others)

1988 Spiral model(Boehm)

7/30/2019 20100317 Clark Spiral

5/24

Introduction

5

Code-and-fix model

First, elementary model

Write code now; fix it later

No planning involvedProblems:

Code is poorly structured.

The software developed was usually a poor match forthe users needs.

7/30/2019 20100317 Clark Spiral

6/24

Introduction

6

Waterfall model

Introduced:

Feedback loops across multiple stages:

Validation and verification steps.Prototyping via a build it twice step alongside of

requirements and design.

Difficulties exposed even as revisions were made to the

model. Required elaborated documents. (Document-driven)

Led to pursuing stages of development in the wrong

order.

7/30/2019 20100317 Clark Spiral

7/24

The spiral model

7

A Typical Cycle of the spiral

Risk Analysis

PrototypeDesign/Validation

Planning

AlternativesAnd repeat

Measure of Cumulative Cost and Progress

7/30/2019 20100317 Clark Spiral

8/24

The spiral model

8

Initiating and terminating the spiral

Four fundamental questions arise in considering thispresentation of the spiral model:

(1) How does the spiral ever get started? (2) How do you get off the spiral when it is

appropriate to terminate a project early?

(3) Why does the spiral end so abruptly?

(4) What happens to software enhancement (ormaintenance)?

7/30/2019 20100317 Clark Spiral

9/24

The spiral model

9

Initiating and terminating the spiral

Initiating the process:

The spiral gets started by a hypothesis that aparticular operational mission (or set of missions)could be improved by a software effort.

Terminating the process:

The spiral process then involves a test of this

hypothesis:At any time, if the hypothesis fails the test, the spiral isterminated.

7/30/2019 20100317 Clark Spiral

10/24

The spiral model

10

7/30/2019 20100317 Clark Spiral

11/24

The spiral model

11

7/30/2019 20100317 Clark Spiral

12/24

The spiral model

12

Cycle Requirements

Each cycle is completed by a review by thepeople concerned with the project.

Plans for the next cycle should be introduced.

With each succeeding level in the spiral thelevel of detail increases.

7/30/2019 20100317 Clark Spiral

13/2413

7/30/2019 20100317 Clark Spiral

14/2414

7/30/2019 20100317 Clark Spiral

15/24

The spiral model

15

PrototypeThrowaway prototypingThrowaway or Rapid Prototyping refers to the creation of a model that

will eventually be discarded rather than becoming part of the finaldelivered software.

Evolutionary prototypingThe main goal when using Evolutionary Prototyping is to build a very

robust prototype in a structured manner and constantly refine it.

Incremental prototyping

The final product is built as separate prototypes. At the end the separateprototypes are merged in an overall design.

Extreme prototypingIt is a development process is used especially for developing web

applications.

7/30/2019 20100317 Clark Spiral

16/24

The spiral model

16

Advantages of prototyping

Reduced time and costs

Improved and increased user involvement

Disadvantages of prototyping

Insufficient analysis

User confusion of prototype and finished system

Developer misunderstanding of user objectivesDeveloper attachment to prototype

Excessive development time of the prototype

Expense of implementing prototyping

7/30/2019 20100317 Clark Spiral

17/24

17

Risk item Risk management techniques

Personnel shortfalls Staffing with top talent, job matching; teambuilding;morale building; cross-training; pre-scheduling key people

Unrealistic schedules

and Budgets

Detailed, multisource cost and schedule estimation;

design to cost; incremental development; software reuse;requirements scrubbing

Developing the wrongsoftware Functions

Organization analysis; mission analysis; ops-conceptformulation; user surveys; prototyping; early usersmanuals

Developing the wronguser Interface

Task analysis; prototyping; scenarios; user characterization(functionality, style, workload)

Gold plating Requirements scrubbing; prototyping; cost-benefit analysis;design to cost

Continuing stream ofrequirement Changes

High change threshold; information hiding; incrementaldevelopment (defer changes to later increments)

Shortfalls in externally

furnished Components

Benchmarking; inspections; reference checking; compatibility

analysisShortfalls in externallyperformed tasks

Reference checking; pre-award audits; award-fee contracts;competitive design or prototyping;Teambuilding

Real-time performanceShortfalls

Simulation; benchmarking; modeling; prototyping;instrumentation; tuning

Straining computer-

science Capabilities

Technical analysis; cost-benefit analysis; prototyping;

reference checking

7/30/2019 20100317 Clark Spiral

18/24

The spiral model

18

The Risk Management Plan

Identify the projects top 10 risk items.

Present a plan for resolving each risk item.Update list of top risk items, plan, and results

monthly.

Highlight risk-item status in monthly project reviews.Compare with previous months rankings, status.

Initiate appropriate corrective actions.

7/30/2019 20100317 Clark Spiral

19/24

Spiral model usage: TRW Software ProductivitySystem, Round 0.--Feasibility study.

19

7/30/2019 20100317 Clark Spiral

20/24

Spiral model usage: TRW Software ProductivitySystem, Round 1.--Concept of operations.

20

7/30/2019 20100317 Clark Spiral

21/24

Spiral model usage: TRW Software Productivity System,Round 2.--Top-level requirements specification.

21

7/30/2019 20100317 Clark Spiral

22/24

Evaluation

22

Advantages Estimates become more realistic as work progresses, because

important issues are discovered earlier. It is more able to cope with the changes that software

development generally entails. Software engineers can get their hands in and start working

on a project earlier.

Disadvantages Highly customized limiting re-usabilityApplied differently for each application Risk of not meeting budget or schedule

7/30/2019 20100317 Clark Spiral

23/24

Conclusions

23

The risk-driven nature provides adaptability for a fullrange of software projects.

The model has been successful in a large application,

the TRW-SPS.The model is not yet fully elaborated.

Even partial implementations of the model, such asthe risk management plan, are compatible with the

other process models.

7/30/2019 20100317 Clark Spiral

24/24

References

24

Rapid Prototyping Tools Revisited

Alan M. Davis, "Operational Prototyping: A newDevelopment Approach. IEEE Software, September 1992.Page 70-78.

Wikipedia: Software Prototyping

B. Boehm, " A Spiral Model of Software Development andEnhancement, ACM SIGSOFT Software Engineering Notes,Volume 11 , Issue 4 (August 1986) Pages: 14 - 24.

Barry Boehm et al., "Using the WinWin Spiral Model: ACase Study, IEEE Computer, July 1998 (vol. 31 no. 7) pp.33-44.