Difference Between ERD and DFD

ERD and DFD are data presentation models that help in identifying the flow of data as well as inputs and outputs. They are important as they enable effective communication between members of different departments in an organization. There are similarities in the two types of data presentation models although there are differences that will be talked about in this article.

DFD’s are systematic representation of how data flows in an organization, how and from where it enters the system, how it moves from one process to another and how it is stored in the organization. On the other hand, a semantic data model of a system in a top down manner is called Entity Relationship Diagram or ERD. ERD demonstrates how a system will look like without telling how to implement it. Since it is entity based, ERD shows the relationship between entities in a system or process. On the other hand, DRD being data flow diagrams focus upon flow of data in a system and how this data is utilized in different stages of a process.

Both DFD and ERD are important for an organization. While entities, whether they are people, places, events or objects are represented in an ERD, DFD talks about how data flows between entities. One gets to know about the entities for which data is stored in the organization through ERD while DFD gives information about the flow of data between entities and how and where it is stored.

Different tools are made use of while preparing DFD and ERD. While it is common to use circles, ovals, rectangles and arrows to make DFD, ERD uses only rectangular boxes. Diamonds are used to represent relationships between entities in ERD and you find description of relationship whereas naming in DFD is through a single word.

Despite their popularity and widespread use, both DFD and ERD are incomplete in the sense that one does not get the full picture looking at either of the two data representation diagrams.

In brief:

• While DFD depicts how the information enters, gets transformed, used and stored in an organization, ERD focuses on entities and how they make use of information in the system.

• ERD just tells how the system ultimately looks like without specifying the process of implementation.

• There are different tools for representation of ERD and DFD