SPEAKER : KAI-JIA CHANG ADVISER : QUINCY WU DATA : Spiral Model

Outline 2  Introduction  The spiral model  Evaluation  Conclusions  References

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.

Introduction 4 Background on software process models  1950 ： Code-and-fix model  1956 ： Stagewise model (Bengington )  1970 ： Waterfall model (Royce)  1971 ： Incremental model(Mills)  1977 ： Prototyping model(Bally and others)  1988 ： Spiral model(Boehm)

Introduction 5 Code-and-fix model  First, elementary model  Write code now; fix it later  No planning involved  Problems: – Code is poorly structured. – The software developed was usually a poor match for the users’ needs.

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.

The spiral model 7 A Typical Cycle of the spiral  Risk Analysis  Prototype  Design/Validation  Planning  Alternatives  And repeat  Measure of Cumulative Cost and Progress

The spiral model 8 Initiating and terminating the spiral Four fundamental questions arise in considering this presentation 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 (or maintenance)?

The spiral model 9 Initiating and terminating the spiral  Initiating the process: – The spiral gets started by a hypothesis that a particular 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 is terminated.

The spiral model 10

The spiral model 11

The spiral model 12 Cycle Requirements  Each cycle is completed by a review by the people concerned with the project.  Plans for the next cycle should be introduced.  With each succeeding level in the spiral the level of detail increases.

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The spiral model 15 Prototype  Throwaway prototyping Throwaway or Rapid Prototyping refers to the creation of a model that will eventually be discarded rather than becoming part of the final delivered software.  Evolutionary prototyping The 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 separate prototypes are merged in an overall design.  Extreme prototyping It is a development process is used especially for developing web applications.

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 objectives  Developer attachment to prototype  Excessive development time of the prototype  Expense of implementing prototyping

17 Risk itemRisk management techniques Personnel shortfallsStaffing 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 wrong software Functions Organization analysis; mission analysis; ops-concept formulation; user surveys; prototyping; early users’manuals Developing the wrong user Interface Task analysis; prototyping; scenarios; user characterization (functionality, style, workload) Gold platingRequirements scrubbing; prototyping; cost-benefit analysis; design to cost Continuing stream of requirement Changes High change threshold; information hiding; incremental development (defer changes to later increments) Shortfalls in externally furnished Components Benchmarking; inspections; reference checking; compatibility analysis Shortfalls in externally performed tasks Reference checking; pre-award audits; award-fee contracts; competitive design or prototyping;Teambuilding Real-time performance Shortfalls Simulation; benchmarking; modeling; prototyping; instrumentation; tuning Straining computer- science Capabilities Technical analysis; cost-benefit analysis; prototyping; reference checking

The spiral model 18 The Risk Management Plan  Identify the project’s 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 month’s rankings, status.  Initiate appropriate corrective actions.

Spiral model usage: TRW Software Productivity System, Round 0. --Feasibility study. 19

Spiral model usage: TRW Software Productivity System, Round 1.--Concept of operations. 20

Spiral model usage: TRW Software Productivity System, Round 2.--Top-level requirements specification. 21

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-usability  Applied differently for each application  Risk of not meeting budget or schedule

Conclusions 23  The risk-driven nature provides adaptability for a full range 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 as the risk management plan, are compatible with the other process models.

References 24 Rapid Prototyping Tools Revisited Alan M. Davis, "Operational Prototyping: A new Development Approach. IEEE Software, September Page Wikipedia: Software Prototyping B. Boehm, " A Spiral Model of Software Development and Enhancement, ACM SIGSOFT Software Engineering Notes, Volume 11, Issue 4 (August 1986) Pages: Barry Boehm et al., "Using the WinWin Spiral Model: A Case Study, IEEE Computer, July 1998 (vol. 31 no. 7) pp