Incremental Model: Evaluation, Incremental vs. Iterative

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Information System (CS507)

The first increment is usually the core product which addresses the basic requirements of the system. This

maybe either be used by the client or subjected to detailed review to develop a plan for the next increment.

This plan addresses the modification of the core product to better meet the needs of the customer, and the

delivery of additionally functionality. More specifically, at each stage

The client assigns a value of functionality to each module not yet implemented

The developer estimates cost of developing each module

The resulting value-to-cost ratio is the criterion used for selecting which module is delivered next

Essentially the module with the highest value-to-cost ratio is the one that provides the client with the most

functionality (value) for the least cost. Using this method the client has a usable product at all of the

development stages. Modules are also selected on the basis of the customer requirements and needs apart

from the value to cost ratio.

20.1 Characteristics of the Incremental Model

The system development is broken into many mini development projects

Partial systems are successively built to produce a final total system.

Highest priority requirements tackled early on.

Once an incremented portion is developed, requirements for that increment are frozen.

20.2 Incremental Model-Evaluation

Benefits

Working functionality is produced earlier computation of value to cost ratio

Reduces risks of change in user requirements

Provides clients flexibility in decision making.

Risk management is incremental

Smaller scope for change in user requirements

Information System (CS507)

Criticism

Larger picture cannot be seen until the entire system is built

Difficult to break down the total system at early stage of product development to determine reasonable

increments

Iterative Models

Iterative models are an approach for developing systems based on producing deliverables

frequently/repetitively. Each iteration, consisting of requirements, analysis & design, implementation and

testing, results in the release of an executable subset of the final product. These subsets grows incrementally

from iteration to iteration to become the final system. The Procedure itself consists of three basic steps.

The Initialization step -- creates a base version of the system. The goal for this initial implementation is

to create a product to which the user can react.

The Iteration step -- The iteration step involves

The redesign and implementation of a task from project control list. The goal for the design and

implementation of any iteration is to be simple, straightforward, and modular, supporting redesign

at that stage or as a task added to the project control list.

The analysis of the current version of the system. The analysis of an iteration is based upon user

feedback and the program analysis facilities available. It involves analysis of the structure,

modularity, usability, reliability, efficiency, and achievement of goals. The project control list is

modified in light of the analysis results.

The Project Control List -- To guide the iteration process, a project control list is created that

contains a record of all tasks that need to be performed. It includes n

New features to be implemented, and

Areas of redesign of the exiting solution.

The control list is constantly being revised as a result of the analysis phase.

20.3 Iterative Models Evaluation

Harms

The Iterative Model can lead to "scope creep," since user feedback following each phase may lead to

increased customer demands. As users see the system develop, they may realize the potential of other

system capabilities which would enhance their work.

Benefits

In fact, the context of multiple iterations provides advantages in the use of measuring various aspects

of product development, such as

Effort to date

Changes,

Defects,

Logical, physical, and dynamic attributes,

Environmental considerations.

Information System (CS507)

The customer can tell how product characteristics like size, complexity, coupling, and cohesion are

increasing or decreasing over time.

One can monitor the relative change of the various aspects of the product or can provide bounds for

the measures to signal potential problems and anomalies.

20.4 Incremental vs. Iterative

These sound similar, and sometimes are equated but there is a subtle difference:

Incremental: add to the product at each phase

Iterative: re-do the product at each phase

Example

Building a House

Incremental: Starts with a modest house, keep adding rooms and upgrades to it.

Iterative: The design/construction map of the house is amended and improved and repeated

until all the requirements are fulfilled.

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