09-10 - Software Process Models

Software Process Models

MS 204/ ES 205 Software Engineering MS - Med Soft (Sem II) MS – Emb.Systems (Sem II)

Process Models • • • • •

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Waterfall / Classical/ Linear Sequential Model Prototyping RAD Model Phased Developments (Increments & Iterative) Spiral

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Waterfall Model Validation: Focus on building right product

Analysi s Design

Verification: Focus on quality of implementation

Coding Testing Installatio n Operation and Maintenance 10/22/08

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Waterfall Model Advantages: • Simple to understand & implement • Document is ready • Testing & Verification at each stage Disadvantages: • Requirements freezing is difficult • Document driven • Large Projects (dev. time is long): Obsolete h/w

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Prototyping

Listen to customer Customer Test drives the prototype

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Build/ Release prototype

• Used when general objectives for software is known

• Detailed I/P, Processing, O/P are not known

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Prototyping Advantages: • More fine-grained requirements can be retrieved from customer • Improves understanding of the customer Disadvantages: • Rework out of control • Cost at later stage is high • Proto. Environment may remain same

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Rapid Application Model (RAD) Business Modeling Data Modeling Process Modeling App Generation Test & Turnover 10/22/08

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Rapid Application Model (RAD) Advantages: • Uses reusable components • Short period for development Disadvantages: • Not good for Tech. Risky Systems • Not all the projects are appropriate for RAD 10/22/08

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Evolutionary Process Models

Phased Development Model

Spiral Model

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Phased Development • • • •

To reduce cycle time Deliver in pieces Operational System – In use : Release n Development System – Under dev. : Release (n + 1)

• Approaches : • Incremental approach • Iterative approach

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Incremental Approach • The system is partitioned into subsystems by functionality • The releases are defined by beginning with one small functional subsystem & then adding functionality with each new release Increment 1

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Increment 2

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Increment 3

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Iterative Approach • Delivers the full systems at the very beginning & then changes (enhancements to) the functionality of each subsystem with each new release.

Iteration 1

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Iteration 2

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Iteration 3

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Phased Development :An Example

Text Processing Package (e.g. MS Word) Incremental R1 R2

Iterative

Creating Text

Provide min. but all functions

(Write text & save it )

(No. of Fonts /Colors: 10)

Organising Text ( Cut & Paste )

Improve the functionalities of all (No. of Fonts /Colors: 256)

R3

Formatting text Enrich the functionalities still more (Changing Font Style, Size) (Choosing custom color)

R4

Objects (Including Images, Charts)

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Enrich still further (Create own font, effect & style)

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Adv & Disadvantages • Adv – Markets can be created for never-beenoffered functionalities – Training can begin at early release – Frequent releases help developers (fix bugs, globally & quickly) • Disadvantages – Too much releases & patches would confuse customers – Tend to postpone the “buy” decisions

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References: • Book: Chapter 2, Software Engineering – Theory & Practice, Shari Lawrence Pfleeger • Book: Chapter 2, Software Engineering – A Practitioner’s Approach, Roger Pressman

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