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180 Part 3 • the analysis Process

The Data Flow Approach to Human
Requirements Determination

When systems analysts attempt to understand the information requirements of users, they must
be able to conceptualize how data move through the organization, the processes or transforma-
tion that the data undergo, and what the outputs are. Although interviews and the investigation of
hard data provide a verbal narrative of the system, a visual depiction can crystallize this informa-
tion for users and analysts in a useful way.
Through a structured analysis technique called data flow diagrams (DFDs), a systems ana-
lyst can put together a graphical representation of data processes throughout an organization. By
using combinations of only four symbols, a systems analyst can create a pictorial depiction of
processes that will eventually provide solid system documentation.

Advantages of the Data Flow Approach
The data flow approach has four chief advantages over narrative explanations of the way data
move through the system:

1. Freedom from committing to the technical implementation of the system too early.
2. Further understanding of the interrelatedness of systems and subsystems.
3. Communicating current system knowledge to users through data flow diagrams.
4. Analysis of a proposed system to determine if the necessary data and processes have been
defined.
Perhaps the biggest advantage lies in the conceptual freedom found in the use of the four
symbols (covered in the upcoming subsection on DFD conventions). (You will recognize three of
the symbols from Chapter 2.) None of the symbols specify the physical aspects of implementa-
tion. DFDs emphasize the processing of data or the transforming of data as they move through a
variety of processes. In logical DFDs, there is no distinction between manual or automated pro-
cesses. Neither are the processes graphically depicted in chronological order. Rather, processes
are eventually grouped together if further analysis dictates that it makes sense to do so. Manual
processes are put together, and automated processes can also be paired with each other. This
concept, called partitioning, is taken up in a later section.

Conventions Used in Data Flow Diagrams
Four basic symbols are used to chart data movement on data flow diagrams: a double square, an
arrow, a rectangle with rounded corners, and an open-ended rectangle (closed on the left side and
open ended on the right), as shown in Figure 7.1. An entire system and numerous subsystems can
be depicted graphically with these four symbols in combination.
The double square is used to depict an external entity (another department, a business, a
person, or a machine) that can send data to or receive data from the system. The external entity,
or just entity, is also called a source or destination of data, and it is considered to be external to
the system being described. Each entity is labeled with an appropriate name. Although it inter-
acts with the system, it is considered as being outside the boundaries of the system. An entity
should be named with a noun. The same entity may be used more than once on a given data flow
diagram to avoid crossing data flow lines.
The arrow shows movement of data from one point to another, with the head of the arrow
pointing toward the data’s destination. Data flows occurring simultaneously can be depicted
doing just that through the use of parallel arrows. Because an arrow represents data about a per-
son, place, or thing, it too should be described with a noun.
A rectangle with rounded corners is used to show the occurrence of a transforming process.
Processes always denote a change in or transformation of data; hence, the data flow leaving a
process is always labeled differently than the one entering it. Processes represent work being
performed in the system and should be named using one of the following formats. A clear name
makes it easier to understand what the process is accomplishing:
1. When naming a high-level process, assign the process the name of the whole system. An
example is INVENTORY CONTROL SYSTEM.