The Incremental Model

The linear sequential model combines the incremental model elements of with the iterative philosophy of prototyping.   As show in the figure the incremental model applies linear sequences in a staggered fashion as   calendar time progress.   Each linear sequence produces as deliverable increment of   the software.   For example word processing software   built using the incremental paradigm might deliver basic file management, document production and editing functions in the first increment more sophisticated document production capabilities and editing in the second increment spelling and grammar checking in the third increment and advanced page layout capability in the 4^th increment. It should be noticed that the process flow for any rise can incorporate the prototyping paradigm.

When    an  incremental  model  is  used the  first  increment  is  often  a  core  product.    That is basic needed are addressed, but many supplementary features like some known, others unknown remain undelivered. The core product is used through the customer or undergoes detailed review.  As a result of use and evaluation a plan is built for the next increment. The plan addresses the adjustment of the core  product to  better meet the  requirement  of  the  customer and  the  delivery of  additional functionality and features.   This process is repeated following the delivery of each increment until the complete product is produced. After increments are stripped down edition of the final product but they do provide capability which serves the user and also give a platform for evaluation through the user.

Figure - The incremental model

Incremental development  is  particularly  useful  when  staffing  is  not available for  a  complete implementation by the business deadline that has been  established for the new project.  Earlier increment can be implemented   with fewer people.   If the core product is well received then additional staff can be added to implement the next increment.  Additionally increments can be planned to maintain technical risks.   For example a major   system might need   the availability of new hardware that is under development and whose delivery date is uncertain.  In might be possible to plan early increments in a way that avoids the use of this hardware thereby to enable partial functionality will be delivered to end users without inordinate delay.