The Incremental Model

The incremental model combines elements of the linear sequential model (applied

repetitively) with the iterative philosophy of prototyping.  the

incremental model applies linear sequences in a staggered fashion as calendar time

progresses. Each linear sequence produces a deliverable “increment” of the software

. For example, word-processing software developed using the incremental

paradigm might deliver basic file management, editing, and document production

functions in the first increment; more sophisticated editing and document production

capabilities in the second increment; spelling and grammar checking in the third

increment; and advanced page layout capability in the fourth increment. It should be

noted that the process flow for any increment can incorporate the prototyping paradigm.

When an incremental model is used, the first increment is often a core product.

That is, basic requirements are addressed, but many supplementary features (some

known, others unknown) remain undelivered. The core product is used by the customer

(or undergoes detailed review). As a result of use and/or evaluation, a plan is

developed for the next increment. The plan addresses the modification of the core

product to better meet the needs of the customer and the delivery of additional

features and functionality. This process is repeated following the delivery of each

increment, until the complete product is produced.

The incremental process model, like prototyping  and other evolutionary

approaches, is iterative in nature. But unlike prototyping, the incremental

model focuses on the delivery of an operational product with each increment. Early

increments are stripped down versions of the final product, but they do provide capability

that serves the user and also provide a platform for evaluation by the user.

Incremental development is particularly useful when staffing is unavailable for a

complete implementation by the business deadline that has been established for the

project. Early increments can be implemented with fewer people. If the core product

is well received, then additional staff (if required) can be added to implement the next

increment. In addition, increments can be planned to manage technical risks.

 For example, a major system might require the availability of new hardware that is under

development and whose delivery date is uncertain. It might be possible to plan early

increments in a way that avoids the use of this hardware, thereby enabling partial

functionality to be delivered to end-users without inordinate delay.