Page 210 - DCAP302_ENTERPRISE_RESOURCE_PLANNING

Enterprise Resource Planning

notes should include, and gave guidance on the conditions that should be met in order that a project
be allowed to proceed from one stage to the next. The aim of this model was to bring control and
discipline to what had previously been a rather unstructured and chaotic process.
The waterfall model involved progressing through a series of different stages, including
requirements definition, specification, planning, design, implementation, and integration.
The emphasis was on preparing a detailed design specification up-front in development, and
thereafter executing on this specification in an efficient manner.
While the waterfall model of development proved to be a successful response to the early
problems that had plagued software development, increasing dissatisfaction was expressed with
its results in the years that followed. The criticism was especially strong in environments where
considerable uncertainty surrounded either the product’s customer requirements and/or its
needed technical solutions.
The problem lay in the assumptions embedded in the model, the biggest of which was that as
long as the up-front work was performed correctly, there was little need to gain intermediate
feedback on performance, or to have a process that was receptive to changing requirements.
Consequently, these became the primary objectives for more “flexible” models of development –
models with the ability to respond to the different types of uncertainty that software developers
increasingly faced.
Over time, this view of software development as a process that could be pro-actively managed
led to the development of other process models, each proposing to address shortfalls with the
waterfall model. While most of these models had a common aim – a more flexible model of
development – the details of their execution appeared to differ substantially. Beginning in the
early 1980’s, a host of more flexible models of development began to emerge, each seeking to
address perceived shortfalls with the waterfall model.
The first types of models that emerged to supplant the waterfall model were based upon the use
of one or more prototypes to be shown to customers at an early stage, thereby gaining feedback
based upon a representation of the product, as opposed to a text specification. In the approach
of prototyping model, use is made of a prototype early in development, typically as a way of
informing decisions about the design of the user interface. The prototypes are thrown away after
use – they are not an integral part of the product. The process that is subsequently used to detail
the design is similar in nature to the waterfall model described above.
The next series of models that emerged from efforts to improve flexibility in development are
characterized by the fact that they involve developing sub-sets of a product’s functionality on an
incremental basis. These are known as Rapid Development Models. The primary objective of the
incremental delivery model is to reduce risk in large projects by delivering subsets of the planned
functionality to customers earlier in development. Development is split into a number of sub-
cycles each of which typically uses a mini-waterfall process, resulting in a complete subsystem
that is delivered to customers.
The latest model is both incremental and iterative. This is called the spiral development model,
which encompasses a feedback mechanism that allows it to

1. Re-work features in these intermediate versions in response to customer feedback
2. Re-schedule subsequent activities in light of the new information generated when each
sub-cycle is completed.

The spiral development model combines the waterfall development model and the prototype
approach, which is a series of partial implementations of the product. Advantages of the
spiral development model include an early focus on reusing existing software components,
the incorporation of software quality standards and the integration of hardware and software
development cycles.

204 LoveLy professionaL university