Introduction to Data Flow Diagrams

Data flow diagrams are very important to structured programming. So I decided to do a little article about DFD’s. Data flow diagrams are also known as bubble charts. It is a visual representation of a system via input data to a system, the number of processes carried out to these data and the final output from the system. Data flow diagrams are so popular because of the simplicity and the clearness of the diagrams. Otherwise you can say they are very formal and easy to understand. Data flow diagrams use specific number of easy symbols to depict the functions and processes with the inputs and outputs of the system. Data flow diagrams are a hierarchical diagram type where representing from the set of most high level functions of the system to the sub level function. Any hierarchical model is easy to understand by the humans because hierarchical models starts very simple with abstract model of a system and different details of the system are introduced slowly. There are simple set of rules when drawing data flow diagrams followed by conceptual techniques. Below are the different symbols that represent and used to construct data flow diagrams. Just have a look and see how simple they are.

I’m going to explain each one of these symbols briefly. Try and understand what each of these means and how to use them in a data flow diagram correctly.

External Entity

External entities are represented by a rectangle and the better examples for external entities are librarian, library member, etc. These external entities represent those physical entities in the real world that interacts with the system. As you can see these external entities are outside to the software system and interacting with the system by inputting data by consuming the data created by the software system.

Process

Functions are represented by a circle. These symbols are called as process or bubbles. This term is derived from the bubble chart terminology. Bubbles are connected with the corresponding functions. 

Data Flow Symbol (Arrow)

An arrow is used to represent the connectors or a data flow symbol. This arrow can be a straight directed arrow as well as a curve arrow according to the structure of the diagram. There are three things that a data flow symbol can represent.

1. Data flow between two processes
2. Between external entity and a process
3. Process in a direction of the data flow arrow

Data flow symbols are usually represented with corresponding data names.

Data Store Symbol

Data stores are where data is basically stores and it is represented by an open box. There for an open box can represent a logical file, data structure or a physical file on disk. Each data source is connected with a process obviously with an arrow or a data flow symbol. The direction of the arrow can represent whether the data is read or write from the disk or into a data source. An arrow flowing in or out of a data store implicitly represents the entire data of the data store and hence arrows connecting to a data source need not be annotated with the name of the corresponding data item. 

Above symbols are created with Creately Org Chart Software.