Data Flow Diagrams Report

This report provides a comprehensive overview of data flow diagrams (DFDs), focusing on the distinction between logical and physical DFDs. It begins by defining DFDs and their role in representing data flow within business information systems. The report then delves into the specifics of each type: logical DFDs, which emphasize business activities and processes, and physical DFDs, which detail the system's implementation using hardware, software, and personnel. Key differences between the two are highlighted, including their focus (business activities vs. system implementation), representation of processes (business activities vs. software programs/manual procedures), and data stores (databases vs. computer files/paper files). The report also underscores the importance of DFDs in program organization, decision-making, and communication with non-technical stakeholders. It further discusses the merits of both logical and physical DFDs, emphasizing their contributions to system stability, maintainability, and efficiency. The report concludes by reiterating the crucial role of DFDs in understanding data flow within a business context and their value in system analysis and design.

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Data Flow Diagram
July 25th, 2019
What is Data Flow Diagram?
In a business information system, some of us have noticed a graphical representation of the
entire flow of data taking place with the help of a diagram. This diagram is known as a data
flow diagram or DFD. A data flow diagram is a graphical representation of the flow of data
taking place in a business information system. It provides ample information about customer
details, account details, transaction history, deposit amount, withdrawn amount, updated
account balance, orders placed, details of the brokers, etc. The processes which are involved
in a business information system in transferring data are graphically represented with the help
of the data flow diagram. The data get transferred to the file manager from the inputs to
generate reports. We can find physical and logical data flow diagrams. The physical data flow
diagram mainly describes the physical implementation of data flow on the logical ground. On
the other hand, the flow of data through a particular system in performing certain specified
functionalities of business is described by the logical data flow diagram. It is important to
understand why a business information system needs to represent the flow of data transfer
with the help of either logical or physical data flow diagram. The graphical representation
taking place through DFD helps in representing the processes and the functions which are
capturing manipulating, storing, and distributing data between the environment of an
information system and the entire information system and also between various system
components. These elements get represented graphically with the help of the data flow
diagram.
Data flow diagram helps in providing logical information and the flow of business
information system. It also helps in determining the requirements of physical system
construction. It enhances notation and simplicity and establishes automatic and manual
system requirements. There are mainly four symbols of data flow diagram such as process,
data store, external entity, and top-down decomposition technique. The process receives data
input and provides output with a different form or content. We can have a simple process
where data are collected and saved in the database. On the other hand, we can also have a
complex process where a report is produced which contains details of monthly sales of any
retail stores. Every process gets assigned with a particular name which helps in identifying

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their functions or performance. Data flow indicates a path through which the data from one
end of the information system moves to the other end. It may represent an element of data.
For example, customer id can be represented in a data flow. Datastore is the repository of
data which is used in representing a situation in the data flow diagram. The situation which is
represented by data stored indicates the retention of data in the system. It is very important in
the data flow diagram because single or multiple processes are needed in the usage and the
recorded data in the data store are used for future references. Top-down decomposition
technique is also known as leveling. It is a method which is used to portray detailed
information of the lower-level data flow diagrams.
Leveling is produced by the help of a series of diagrams having more detailed information
until the desired detailing gets achieved. An external entity is a department or a person or an
outside organization which provides information and data to the information system and also
receives output from the information system. External entities can also be defined as the
components found in the outer boundaries of a business information system. The external
entities help represent the interactions between the outside world and the information system.
The external entity is represented by a rectangle in the data flow diagram. These external
entities either receive data or supply data but they do not process data. There is a difference
between physical and logical data flow diagrams. The physical data flow diagram portrays
the ways the system would be implemented. On the other hand, logical data flow diagram
portrays on the ways business gets operated and it mainly focuses on the core areas of the
business.
Two types of Data Flow Diagram-Logical and Physical Data Flow Diagram
Logical Data Flow Diagram
There are two types of data flow diagram logical and physical data flow diagram. Logical
data flow diagram is that type of data flow diagram which mainly focuses on business
activities and the business as a whole. It can be considered as the fundamental basis of
physical data flow diagram because by modifying the logical data flow diagram, we can get
the physical data flow diagram. Logical data flow diagram explains data and business events
which are necessary to accomplish the business events. A physical data flow diagram can be
developed based on a logical data flow diagram. Physical data flow diagram depicts the
working of the data in the system with the support of paper files, Software, Hardware, and

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people involved. The flow of business activities and actions are mapped by the help of a
logical data flow diagram. The inefficiencies and shortcomings of a system get clarified by
the help of a logical data flow diagram. The steps involved in data process in eliminating and
modifying the data are also obtained from the logical data flow diagram. The non-technical
people can easily understand the mechanism of a logical data flow diagram. It is a commonly
observed diagram in any business. The functionality can be understood with the help of a
logical data flow diagram even without implementation. Logical data flow diagrams also
provide in-depth information and help in understanding the system. It helps to identify
shortcomings, inefficiencies, and mistakes. It is an essential diagram because it helps to
eliminate the risks associated with data processing in the system. It elaborates the flow of
data so that functionalities can be made better without technical solutions or without
implementing the actual system. Logical data flow diagram helps to explain the ways a
business can be operated or business gets operated in real. It mainly explains the business
activities. The data store of the logical data flow diagram represents the collection of data
regardless of the ways such data have been stored. The data source for the logical data flow
diagram represents only the collections of permanent data. The business controls are well-
depicted by the help of a logical data flow diagram.
Physical Data Flow Diagram
A physical data flow diagram is created after the creation of a logical data flow diagram.
Physical data flow diagram explains the best-suited method to implement any business
activity. It is involved in the physical implementation of various inter-related devices and
files which are required for processes of the business. Physical data flow diagrams provide
detailed information about external components, hardware, software, and people involved to
operate the business processes. It is mainly concerned with the ways the system can be
implemented or explains the operations of the current system in a business. It presents the
program modules, programs, and manual procedures. The data stored of physical data flow
diagram represent databases, physical files, and manual files. Different sources of data such
as transaction files and master files are found in the case of physical data flow diagrams. Any
processes which can operate at different times should get connected by a particular data
source. Physical data flow diagrams show various controls which are needed to validate input
data or to obtain a record. These controls help ensure effective completion of any process or
system security.

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Difference between Physical and Logical Data Flow Diagrams
The logical data flow diagram is not at all concerned with the ways the information system
gets constructed. Therefore, in the case of logical data flow diagram we can easily overlook
implementation specifics like data storage, technology, computer configuration, message
passing methods for communication and the focus can be given on the actual performance of
the system. The system is engaged in performing data, collection data, information
transformation, and reporting. Physical data flow diagram represents the ways the
information system or the system dealing with information and data can be implemented. It
includes software, hardware, people, and files to get engaged in the system. It is mainly
developed in such a way that the processes which are described by the help of logical data
flow diagrams can be implemented accurately to meet the business goals. The major
difference between physical and logical data flow diagrams is related to their focus because
physical data flow diagrams mainly focus on the implementation of the system and the other
hand, logical data flow system focuses on business activities. Data flow diagrams mainly
explain the data flow taking place in a business information system.
Logical data flow diagram depicts the ways a business operates and the physical data flow
diagram shows the ways the information system is implemented. The main focus of logical
DFD is business activities and the main focus of physical DFD is the implementation of the
system. So, the differences between physical and logical data flow diagrams mainly come
from their focus. A process is considered to be a business activity under the logical data flow
diagram. But a process is considered to be a software program or any manual procedure
under a physical data flow diagram. Datastore is another area where we can find the
difference between logical and physical data flow diagram. Datastore in a logical data flow
diagram depicts the explanation of the ways the data are stored in different databases. Under
physical data flow diagram, data store means computer files, databases, and paper files. The
ways the data gets stored in the databases, paper files, or computer files are explained by a
logical data flow diagram descriptively. A logical data flow diagram can be understood by a
non-technical person but a physical data flow diagram is highly complex and it can only be
interpreted by the persons having prior knowledge and technical skills. Therefore, it can be
said that the data flow diagram represents the flow of data of processes or a system. Logical
and physical data flow diagrams or two types of data flow diagrams and they are different

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from each other. It can also be said that the physical data flow diagram comes from a logical
data flow diagram.
Why are Data Flow Diagrams Important?
The most significant aspect of a data flow diagram is that it helps in keeping the program
highly organized. The programmers can use data flow diagrams in planning the
accomplishment of new programs efficiently. The programmers can also keep a constant
track on the program with the help of data flow diagrams. In the domain of decision-building,
the role of data flow diagrams is highly crucial. In every program which is available to
consumers, we can find there are several parts which help in making decisions based on the
data. Such decisions can be taken either by any part of the program or by the users. Data flow
diagrams support the programmers to figure out various options with the help of which the
programs can be handled and data can be obtained. Data flow diagrams can help the
programmers to explain the functionalities of the program to any laypeople without using any
technical terminologies or computer languages which might not be understood by the
laypeople. By the help of data flow diagrams, the programmers can explain the program to
the people without wasting any time and effort in explaining different computer codes and
languages to the non-technical people. Sometimes, the programmers realize the fact that
there is always an effective way of optimizing the code. This realization takes place during a
project is in its ongoing phase when the programmers find it difficult to figure out where to
use the code. The programmers might also need to modify the codes so that they could
accommodate them feasibly. But with the use of a data flow diagram, the programmers can
able to visualize the consequences of injecting certain codes into the program.
In understanding the logical movement of data in a business, the role of data flow diagrams
can never be overemphasized. The systems analysts structure data flow diagrams as a tool
which helps in depicting interrelated data flows and subsystems of an information system. By
the help of graphical representation of the movement of data storage and data transformation,
the entire information can be obtained. The analysts usually gather sources of data processes
data flows and data stores from initial organizational narratives which are provided by the
users or get revealed by any data sources. This information is used to develop data flow
diagram based on the contexts available. The data flow diagram intricately explains the
performance of the processes by different users, execution of the processes, performance of
similar processes, combination of batch processes for effective processing, the combination

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of processes and partitioning of the processes into different programs. These are the main
areas which get represented by the help of data flow diagrams.

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Merits of Logical Data Flow Diagram
There are certain \benefits of logical data flow diagrams. Logical data flow diagram presents
business information focusing on different business activities which enhances the
communication and the performance of the communication tool when it is used the project
users. It is developed based on business events where physical arrangements or particular
technological resources are not required. It enhances the stability of the resulting system.
Logical data flow diagram also helps the analysts to understand the fact that the business has
been studied upon intricately and it also supports in identifying the fundamental reasons
behind the implementation plans. The system which is implemented on the logical data flow
diagram can be maintained easily because business activities do not get frequently changed.
Logical data flow diagram does not include any data store. It only contains a database which
makes logical data flow diagrams less complex as compared to that of a physical data flow
diagram. Moreover, the logical data flow diagram is much easier to get developed. Physical
data flow diagrams can be formed by making certain modifications in a logical data flow
diagram.
Merits of Physical Data Flow Diagram
There are certain benefits of physical data flow diagrams. Physical data flow diagram
clarifies the manually developed processes and the processes which are automated in nature.
Manual processes demand detailed documentation. On the other hand, an automated process
can be developed with the help of a computer program. Physical data flow diagrams provide
details information about the processes including every step of processing the data. It also
provides sequential information of the processes which helps in understanding the sequence
of business activities appropriately. Physical data flow diagrams help in identifying the data
storage which is temporary. Temporary data storage includes a sales transaction file and a
report on customer receipts. It also specifies actual file names and printouts. It also describes
actual reports and filenames and helps the programmers to relate such data with data
dictionary while they develop the system. It adds more control to enhance the efficiency of
the performance of the processes. There are certain validations or conditions of data which
are required to be met during the process of input, delete, update, and other data processing
activities.

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