Data Flow Diagram (DFD) and Entity Relationship Diagram (ERD) are used for data flow representation. In this article, we will look into DFD and ERD and we will also see the difference between DFD and ERD.
What is Data Flow Diagram (DFD)?
Data means information, flow means to move, and a diagram means a picture to represent something. So, DFD is simply the graphical representation of the flow of data or information. It is a framework or pattern of the data systems. It includes data input, data output, and storing data. DFD describes the process of taking the data as input, storing the data, and giving the data as output. DFD describes the path of data that completes the process. There are mainly two types of DFD: Physical Data Flow Diagram, and Logical Data Flow Diagram.
Example of DFD
- Lemonade Stand
Data Flow Diagram
What is Entity Relationship Diagram (ERD)?
ERD is also known as the Entity-Relationship Model. ERD was originally proposed by Peter Chen. Entity means any object used to store information and are distinguishable, relationship means connection, and diagram/model means a picture uses to represent something. So, ERD is simply the diagram or model that is used to represent or show the relationship between the entities or data objects that are stored in a database. The main components of the E-R model are an entity, attributes, and relationship. It is a very easy way to represent the database design.
Example of ERD
- School Information Management
Entity Relationship Diagram
Differences Between DFD and ERD
| DFD | ERD |
|---|---|
| It stands for Data Flow Diagram. | It stands for Entity Relationship Diagram or Model. |
| Main objective is to represent the processes and data flow between them. | Main objective is to represent the data object or entity and relationship between them. |
| It explains the flow and process of data input, data output, and storing data. | It explains and represent the relationship between entities stored in a database. |
| Symbols used in DFD are: rectangles (represent the data entity), circles (represent the process), arrows (represent the flow of data), ovals or parallel lines (represent data storing). | Symbols used in ERD are: rectangles (represent the entity), diamond boxes (represent relationship), lines and standard notations (represent cardinality). |
| Rule followed by DFD is that at least one data flow should be there entering into and leaving the process or store. | Rule followed by ERD is that all entities must represent the set of similar things. |
| It models the flow of data through a system. | It model entities like people, objects, places and events for which data is stored in a system. |
Previous Year Questions
Q.1: A black hole in a DFD is a: [UGC NET CSE June Paper II]
(A) A data store with no inbound flows
(B) A data store with only inbound flows
(C) A data store with more than one inbound flow
(D) None of these
Solution: Correct Answer is (B).
Q.2: A context model of a software system can be shown by drawing which Level of DFD [ISRO CS 2011]
(A) LEVEL-0 DFD
(B) LEVEL-1 DFD
(C) LEVEL-2 DFD
(D) LEVEL-3 DFD
Solution: Correct Answer is (A).
Q. 3: A physical DFD specifies [ISRO CS 2007]
(A) what processes will be used
(B) who generates data and who processes it
(C) what each person in an organization does
(D) which data will be generated
Solution: Correct Answer is (B).
For detailed explanation, refer to ISRO | ISRO CS 2007 | Question 77.
Frequently Asked Questions on DFD and ERD
Q.1: What are the 4 components of DFD?
Answer:
The 4 components of DFD are Entity, Process, Data Store and Data Flow.
Q.2: What is a weak entity in ER diagram?
Answer:
Weak entity is represented with a double rectangle box. Weak entity does not have primary key.
Q.3: What are 3 levels of abstraction in ERD ?
Answer:
The three levels of abstraction in ERD are View, Logical and Physical.
