Models

1. Software Myths
Software is easy to change
Computers provide greater reliability than the devices they
replace.
Testing software or ‘proving’ software correct can remove all
the errors.
Reusing software increases safety.
Software can work right the first time.
Software can be designed thoroughly enough to avoid most
integration problems.
Software with more features is better software.
Aim is to develop working programs.

2. Generic Software Process Models
There are many different software process models. Here are just
four
The waterfall model
Separate and distinct phases of specification and development;
(more below)
 Evolutionary development
Specification and development are interleaved (more below)
 Formal transformation
A mathematical system model is formally transformed to an
implementation
Reuse-based development
The system is assembled from existing components

3. The Waterfall Model
The waterfall model has separate and distinct phases of
specification and development. These
are:
 Requirements analysis and definition
 System and software design
Implementation and unit testing
Integration and system testing
 Operation and maintenance

4. Waterfall Model

5. Advantage
Progress can be conclusively identified
(through the use of milestones) by both
vendor and client.
Ensures minimal wastage of time and effort.
Reduces the risk of schedule slippage, or of
customer expectations not being met.

6. Prototyping Model
A type of development in which
emphasis is placed on developing
prototypes early in the development
process to permit early feedback and
analysis in support of the
development process.”

7. Need for prototyping
As a requirements artifact to initially envision
the system.
As a design artifact that enables us to explore the
solution space of your system.
 A vehicle for you to communicate the possible
UI design(s) of your system.
 A potential foundation from which to continue
developing the system

8. Prototyping Process
Goals
Functionality
Evaluate
Develop

9. Spiral Model
The Spiral Development ( or Lifecycle)
Model is a systems development method
used in information technology.
It combines the features of the
prototyping model and the waterfall
model.
It is favored for large, expensive, and
complicated models.

10. Steps of the Spiral Model
Define the problem with as much detail as
possible by interviewing the client and
potential users of the system, as well as,
studying any existing system.
A preliminary design is created for the new
system.
A first prototype of the new system is
constructed from the preliminary design and is
a scaled down version of the final product.