Spiral Model SPEAKER KAIJIA CHANG ADVISER QUINCY WU

Spiral Model SPEAKER : KAI-JIA CHANG ADVISER : QUINCY WU DATA : 2010 -03 -17

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

Introduction A Risk-Driven Approach Ø Different idea of software development. Ø How does this project affect the developers and the clients? Ø How does each step in the project affect its overall development? Ø Not used in previous development models. – Usually code-driven or document-driven. 3

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

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

Introduction Waterfall model Ø Introduced: – Feedback loops across multiple stages: Validation and verification steps. – Prototyping via a “build it twice” step alongside of requirements and design. Ø 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. 6

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

The spiral model Initiating and terminating the spiral Four fundamental questions arise in considering this presentation of the spiral model: Ø (1) How does the spiral ever get started? Ø (2) How do you get off the spiral when it is appropriate to terminate a project early? Ø (3) Why does the spiral end so abruptly? Ø (4) What happens to software enhancement (or maintenance)? 8

The spiral model Initiating and terminating the spiral Ø 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. Ø 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. 9

The spiral model 10

The spiral model 11

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

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The spiral model Prototype Ø 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. Ø Evolutionary prototyping The main goal when using Evolutionary Prototyping is to build a very robust prototype in a structured manner and constantly refine it. Ø Incremental prototyping The final product is built as separate prototypes. At the end the separate prototypes are merged in an overall design. Ø Extreme prototyping It is a development process is used especially for developing web applications. 15

The spiral model Advantages of prototyping Ø Reduced time and costs Ø Improved and increased user involvement Disadvantages of prototyping Ø Insufficient analysis Ø User confusion of prototype and finished system Ø Developer misunderstanding of user objectives Ø Developer attachment to prototype Ø Excessive development time of the prototype Ø Expense of implementing prototyping 16

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 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 plating Requirements 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 computerscience Capabilities Technical analysis; cost-benefit analysis; prototyping; reference checking 17

The spiral model The Risk Management Plan Ø Identify the project’s top 10 risk items. Ø Present a plan for resolving each risk item. Ø Update list of top risk items, plan, and results monthly. Ø Highlight risk-item status in monthly project reviews. Compare with previous month’s rankings, status. Ø Initiate appropriate corrective actions. 18

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 Advantages Ø Estimates become more realistic as work progresses, because important issues are discovered earlier. Ø It is more able to cope with the changes that software development generally entails. Ø Software engineers can get their hands in and start working on a project earlier. Disadvantages Ø Highly customized limiting re-usability Ø Applied differently for each application Ø Risk of not meeting budget or schedule 22

Conclusions Ø The risk-driven nature provides adaptability for a full range of software projects. Ø The model has been successful in a large application, the TRW-SPS. Ø The model is not yet fully elaborated. Ø Even partial implementations of the model, such as the risk management plan, are compatible with the other process models. 23

References l l l Rapid Prototyping Tools Revisited Alan M. Davis, "Operational Prototyping: A new Development Approach. IEEE Software, September 1992. Page 70 -78. 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: 14 - 24. Barry Boehm et al. , "Using the Win Spiral Model: A Case Study, IEEE Computer, July 1998 (vol. 31 no. 7) pp. 33 -44. 24