3.9.2 Data Flow Diagram (DFD)

3.9.2 Data Flow Diagram (DFD)
DFD or Data Flow Diagram is a graphical representation that showing the flow of data of information system. It also shows the structured design of the program to replace the flowchart or pseudo code as program tool. Basically DFD can be divided into four components such as entity or external entity, process, data store and data flow. DFD start with an overview of the system that needs to be designed. This DFD known as context DFD that contain the entity and the process only. DFD can be expanded into certain level depending on the processes of the design system or program. There are such methods like top down analysis or breaking down DFDs that usually known as leveling.
Entity/ External Entity
An entity is the
In simple word, it functions to receive input and produce some output. In the diagram, processes represent as ellipse shape, circle or segmented rectangle and include a process name and process number. The process name uses simple verb such as display homepage, transfer money, validate credit card, process invoice, submit payment and
Entities tell the characteristic of the entity, or property, trait relationship, or another attribute. The examples such as the Employee is the entity and Employee ID, Employee Name, Employee Designation is some kind of attributes that related to Employee. There are also attributes that have their own specific attributes to specify more details about the attributes that known as composite attribute. For example attribute receipt that can have receipt number, table number, cashier name, GST registration number, date and time. There are some highest levels ERD that show attributes in order to show the simplicity of the diagram. . It represented in ER diagrams by an oval shapes.

Relationship
As the name relationship, it relates or interacts between two entities. It is usually implemented in computing data that contains databases or information systems.We can see that how carpenter have relationship with table by using relationship makes or builds as shown in figure 38 below. In the diagram the relationship always using verbs and represented by diamond shapes
There are three types of relationship
• One-to-One
One entity connects to another one entity that has only one instances. For example, one Employee allows having one parking lot. In the ERD diagram, it represented by normal single line at both entities as figure 40