Information Technology Reference
In-Depth Information
The order of operations performed in the overall application, and
the flow of control across the modules
Irrespective of which design methodology one decides to pursue, we
have found the concepts under Hierarchy plus Input-Process-Output
(HIPO), in fact HIPO-II, to lay a very good foundation to the design.
Although HIPO was developed during the 1970s for systems analysts and
designers, it never gained popularity as a tool for designing software. At
the core, it contains:
. This shows the decomposition and interrelationships
between modules and components of a system. It looks like an
org chart.
Hierarchy
Input-process-output (IPO) specification: for each module.
The
designer can choose the level of detail for the specification, starting
with just diagrams for the simpler modules, to even pseudo-code
for the complex ones.
We do not say that HIPO should be used for application design. Our
claim is that the concepts embodied in it with respect to decomposing
and representing a system are very powerful and become a good orga-
nizing influence for the designer. Another advantage of HIPO is the
diagramming and visualization aspect. We believe it is very important that
a designer be visually oriented; that is, he or she should be able to
visualize the organization of an application and how each module fits in
with respect to user needs. Using HIPO, as one builds the hierarchy, one
defines the associated IPOs. Each of these definitions will raise further
questions, which will require one to break a module into sub-modules,
if the IPO seems complex. Once one has a rough sketch prepared, one
can move to creating use cases, sequence diagrams, class diagrams, or
whichever methodology one chooses to follow.
A Note on Design Patterns
In 1991, Yourdan and Coad introduced the concept of
object-oriented
design
(OOD). In 1994, Gamma, Helm, Johnson, and Vlissides, known as
the “Gang of Four,” wrote a topic on design patterns; in it they discussed
“recurring solutions to common problems in software design.” Patterns
have changed the way we design systems in today's world. One fact that
most people do not know is that the Gang of Four's work was based on
“patterns” that were introduced by Alexander, Ishikawa, Silverstein, et al.
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