The Spiral Model

The spiral model, originally proposed by Boehm , is an evolutionary software

process model that couples the iterative nature of prototyping with the controlled and

systematic aspects of the linear sequential model. It provides the potential for rapid

development of incremental versions of the software. Using the spiral model, software

is developed in a series of incremental releases. During early iterations, the

incremental release might be a paper model or prototype. During later iterations,

increasingly more complete versions of the engineered system are produced.

A spiral model is divided into a number of framework activities, also called task

regions.6 Typically, there are between three and six task regions. A spiral model

 that contains six task regions:

• Customer communication—tasks required to establish effective communication

between developer and customer.

• Planning—tasks required to define resources, timelines, and other projectrelated

information.

• Risk analysis—tasks required to assess both technical and management

risks.

• Engineering—tasks required to build one or more representations of the

application.

• Construction and release—tasks required to construct, test, install, and

provide user support (e.g., documentation and training).

• Customer evaluation—tasks required to obtain customer feedback based

on evaluation of the software representations created during the engineering

stage and implemented during the installation stage.

Each of the regions is populated by a set of work tasks, called a task set, that are

adapted to the characteristics of the project to be undertaken. For small projects, the

number of work tasks and their formality is low. For larger, more critical projects,

each task region contains more work tasks that are defined to achieve a higher level

of formality

.

As this evolutionary process begins, the software engineering team moves around

the spiral in a clockwise direction, beginning at the center. The first circuit around

the spiral might result in the development of a product specification; subsequent

passes around the spiral might be used to develop a prototype and then progressively

more sophisticated versions of the software. Each pass through the planning region

results in adjustments to the project plan. Cost and schedule are adjusted based on

feedback derived from customer evaluation. In addition, the project manager adjusts

the planned number of iterations required to complete the software.

Unlike classical process models that end when software is delivered, the spiral

model can be adapted to apply throughout the life of the computer software. An alternative

view of the spiral model can be considered by examining the project entry point

axis. Each cube placed along the axis can be used to represent

the starting point for different types of projects. A “concept development

project” starts at the core of the spiral and will continue (multiple iterations occur

along the spiral path that bounds the central shaded region) until concept development

is complete. If the concept is to be developed into an actual product, the process

proceeds through the next cube (new product development project entry point) and

a “new development project” is initiated. The new product will evolve through a number

of iterations around the spiral, following the path that bounds the region that has

somewhat lighter shading than the core. In essence, the spiral, when characterized

in this way, remains operative until the software is retired. There are times when the

process is dormant, but whenever a change is initiated, the process starts at the appropriate

entry point .

The spiral model is a realistic approach to the development of large-scale systems

and software. Because software evolves as the process progresses, the developer and

customer better understand and react to risks at each evolutionary level. The spiral model

uses prototyping as a risk reduction mechanism but, more important, enables the developer

to apply the prototyping approach at any stage in the evolution of the product. It

maintains the systematic stepwise approach suggested by the classic life cycle but incorporates

it into an iterative framework that more realistically reflects the real world. The

spiral model demands a direct consideration of technical risks at all stages of the project

and, if properly applied, should reduce risks before they become problematic.

But like other paradigms, the spiral model is not a panacea. It may be difficult to

convince customers (particularly in contract situations) that the evolutionary approach

is controllable. It demands considerable risk assessment expertise and relies on this

expertise for success. If a major risk is not uncovered and managed, problems will

undoubtedly occur. Finally, the model has not been used as widely as the linear

sequential or prototyping paradigms. It will take a number of years before efficacy of

this important paradigm can be determined with absolute certainty.

Walkthrough & Inspection

Review is "A process or meeting during which artifacts of software product are examined by project stockholders, user representatives, or other interested parties for feedback or approval”. Software Review can be on Technical specifications, designs, source code, user documentation, support and maintenance documentation, test plans, test specifications, standards, and any other type of specific to work product, it can be conducted at any stage of the software development life cycle.

Purpose of conducting review is to minimize the defect ratio as early as possible in Software Development life cycle. As a general principle, the earlier a document is reviewed, the greater will be the impact of its defects on any downstream activities and their work products. Magnitude cost of defect fixing after the release of the product is around 60-100x. Review can be formal or informal. Informal reviews are referred as walkthrough and formal as Inspection.

Walkthrough: Method of conducting informal group/individual review is called walkthrough, in which a designer or programmer leads members of the development team and other interested parties through a software product, and the participants ask questions and make comments about possible errors, violation of development standards, and other problems or may suggest improvement on the article, walkthrough can be pre planned or can be conducted at need basis and generally people working on the work product are involved in the walkthrough process.
The Purpose of walkthrough is to:
· Find problems
· Discuss alternative solutions
· Focusing on demonstrating how work product meets all requirements.IEEE 1028 recommends three specialist roles in a walkthrough:
Leader: who conducts the walkthrough, handles administrative tasks, and ensures orderly conduct (and who is often the Author)
Recorder: who notes all anomalies (potential defects), decisions, and action items identified during the walkthrough meeting, normally generate minutes of meeting at the end of walkthrough session.
Author: who presents the software product in step-by-step manner at the walk-through meeting, and is probably responsible for completing most action items.

Walkthrough Process: Author describes the artifact to be reviewed to reviewers during the meeting. Reviewers present comments, possible defects, and improvement suggestions to the author. Recorder records all defect, suggestion during walkthrough meeting. Based on reviewer comments, author performs any necessary rework of the work product if required. Recorder prepares minutes of meeting and sends the relevant stakeholders and leader is normally to monitor overall walkthrough meeting activities as per the defined company process or responsibilities for conducting the reviews, generally performs monitoring activities, commitment against action items etc.

Inspection: An inspection is a formal, rigorous, in-depth group review designed to identify problems as close to their point of origin as possible., Inspection is a recognized industry best practice to improve the quality of a product and to improve productivity, Inspections is a formal review and generally need is predefined at the start of the product planning, The objectives of the inspection process are to
· Find problems at the earliest possible point in the software development process
· Verify that the work product meets its requirement
· Ensure that work product has been presented according to predefined standards
· Provide data on product quality and process effectiveness
· Inspection advantages are to build technical knowledge and skill among team members by reviewing the output of other people
· Increase the effectiveness of software testing.
IEEE 1028 recommends three following roles in an Inspection:
Inspector Leader: The inspection leader shall be responsible for administrative tasks pertaining to the inspection, shall be responsible for planning and preparation, shall ensure that the inspection is conducted in an orderly manner and meets its objectives, should be responsible for collecting inspection data
Recorder: The recorder should record inspection data required for process analysis. The inspection leader may be the recorder.
Reader: The reader shall lead the inspection team through the software product in a comprehensive and logical fashion, interpreting sections of the work product and highlighting important aspects
Author: The author shall be responsible for the software product meeting its inspection entry criteria, for contributing to the inspection based on special understanding of the software product, and for performing any rework required to make the software product meet its inspection exit criteria.
Inspector: Inspectors shall identify and describe anomalies in the software product. Inspectors shall be chosen to represent different viewpoints at the meeting (for example, sponsor, requirements, design, code, safety, test, independent test, project management, quality management, and hardware engineering). Only those viewpoints pertinent to the inspection of the product should be present. Some inspectors should be assigned specific review topics to ensure effective coverage. For example, one inspector may focus on conformance with a specific standard or standards, another on syntax, and another for overall coherence. These roles should be assigned by the inspection leader when planning the inspection.
All participants in the review are inspectors. The author shall not act as inspection leader and should not act as reader or recorder. Other roles may be shared among the team members. Individual participants may act in more than one role. Individuals holding management positions over any member of the inspection team shall not participate in the inspection
Inspection Process: Following are review phases:
· Planning
· Overview
· Preparation
· Examination meeting
Planning:
· Inspection Leader perform following task in planning phase
· Determine which work products need to be inspected
· Determine if a work product that needs to be inspected is ready to be inspected
· Identify the inspection team
· Determine if an overview meeting is needed.
The moderator ensures that all inspection team members have had inspection process training. The moderator obtains a commitment from each team member to participate. This commitment means the person agrees to spend the time required to perform his or her assigned role on the team. Identify the review materials required for the inspection, and distribute materials to relevant stake holders
Overview: Purpose of the overview meeting is to educate inspectors; meeting is lead by Inspector lead and is presented by author, overview is presented for the inspection, this meeting normally acts as optional meeting, purpose to sync the entire participant and the area to be inspected.
Preparation: Objective of the preparation phase is to prepare for the inspection meeting by critically reviewing the review materials and the work product, participant drill down on the document distributed by the lead inspector and identify the defect before the meeting
Examination meeting: The objective of the inspection meeting is to identify final defect list in the work product being inspected, based on the initial list of defects prepared by the inspectors [identified at preparation phase and the new one found during the inspection meeting. The Lead Auditor opens the meeting and describes the review objectives and area to be inspected. Identify that all participants are well familiar with the content material, Reader reads the meeting material and inspector finds out any inconsistence, possible defects, and improvement suggestions to the author. Recorder records all the discussion during the inspection meeting, and mark actions against the relevant stake holders. Lead Inspector may take decision that if there is need of follow up meeting. Author updates the relevant document if required on the basis of the inspection meeting discussion
Rework and Follow-up: Objective is to ensure that corrective action has been taken to correct problems found during an inspection.