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CHAPTER 11 ANALYSIS CONCEPTS AND PRINCIPLES 285

FIGURE 11.3
Information
Input Intermediate Output
flow and
object(s) data and control object(s)
transformation Transform Transform
#1 #2

Data/control
store

are distinct structures to be used? How does information in one information struc-
ture relate to information in another structure? These questions and others are
answered by an assessment of information structure. It should be noted that data
structure, a related concept discussed later in this book, refers to the design and imple-
mentation of information structure within the software.

11.3.2 Modeling

We create functional models to gain a better understanding of the actual entity to be
built. When the entity is a physical thing (a building, a plane, a machine), we can build
a model that is identical in form and shape but smaller in scale. However, when the
entity to be built is software, our model must take a different form. It must be capa-
ble of representing the information that software transforms, the functions (and sub-
functions) that enable the transformation to occur, and the behavior of the system as
the transformation is taking place.
The second and third operational analysis principles require that we build mod-
? What types els of function and behavior.
of models
do we create Functional models. Software transforms information, and in order to
accomplish this, it must perform at least three generic functions: input, pro-
during
requirements cessing, and output. When functional models of an application are created,
analysis? the software engineer focuses on problem specific functions. The functional
model begins with a single context level model (i.e., the name of the software
to be built). Over a series of iterations, more and more functional detail is
provided, until a thorough delineation of all system functionality is repre-
sented.
Behavioral models. Most software responds to events from the outside
world. This stimulus/response characteristic forms the basis of the behav-
ioral model. A computer program always exists in some state—an externally
observable mode of behavior (e.g., waiting, computing, printing, polling) that
is changed only when some event occurs. For example, software will remain