What is a Data Flow Diagram (DFD)?
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Data Flow Diagrams (DFDs) are an essential tool in software engineering that enables analysts to represent the flow of data within a system. DFDs provides a graphical representation of the system’s inputs, outputs, and the various processing steps that transform the inputs into the desired outputs. They are particularly useful in identifying the various data sources, data stores, and data transformations that are involved in a software system.
By using DFDs, software engineers can better understand the interactions between various components of a system, which can help to develop software that is more efficient, effective, and better meets the needs of the stakeholders. In this way, DFDs can play a critical role in software development, from the requirements-gathering phase to the final testing and deployment of a system.
These Data Flow Diagrams provide an overview of the following:
- Provides an overview of the data that the system processes.
- Depicts the various transformations that are performed on the data.
- Illustrates the data that is stored within the system.
- Shows the different results that are produced by the system.
- Enables analysts to understand the interconnections between various components of the system.
- Aids in the identification of data sources, data stores, and data transformations within a software system.
- Helps to develop software that is more efficient, effective, and better meets the needs of the stakeholders.
- Plays a critical role in software development, from the requirements gathering phase to the final testing and deployment of a system.
Essential Observations for DFDs
- All names used in DFDs must be unique to make it easier to refer to individual elements within the diagram.
- DFDs are not flowcharts, and as such, arrows represent the flow of data, not the order of events.
- Logical decisions should be suppressed in DFDs. Diamond-shaped boxes, commonly used in flowcharts to represent decision points, should not be included in DFDs.
- Details should be avoided in DFDs. Analysts should defer error conditions and error handling until the end of the analysis.
DFD Creating Rules
- The names of the entities included in the DFD should be clear, concise, and easily understandable without the need for additional comments or explanation.
- Processes should be either numbered or listed in an ordered manner to facilitate easy reference.
- Consistency should be maintained across all DFD levels to ensure coherence and avoid confusion.
- A single DFD should have a minimum of 3 processes and a maximum of 9 processes, in order to maintain a manageable level of complexity and make the diagram easier to understand.
Symbols Used in Creating DFDs
- Square Box (Entity): A square box represents the source or destination of data within the system, and is also known as an entity. This symbol is typically represented by a rectangle.
- Arrow or Line: An arrow or line indicates the movement of data within the system. This symbol helps to identify the flow of data between entities, processes, and data stores.
- Circle or Bubble Chart (Process): A circle or bubble chart represents a process in the system that transforms input data into output data, and is also known as a processing box. This symbol represents the activities or operations performed on the data within the system.
- Open Rectangle (Data Store): An open rectangle represents a data store where data is stored either temporarily or permanently. This symbol is used to represent a location where data is held for later use and can be used to show where data is retrieved from or stored during the system’s operation.
Levels in Data Flow Diagram
0-level DFD:
- The highest level of parent level in the DFD hierarchy.
- Provides an overview of the entire system being analyzed.
- It consists of only one process representing the entire system.
- This level focuses on the external entities that interact with the system and the data flows between them.
1-level DFD:
- The first level of decomposition of the parent process is in the 0-level DFD.
- It represents a more detailed view of the system.
- At this level, the parent process is divided into a set of smaller, more manageable sub-processes.
- The external entities and data flows are also depicted at this level.
2-level DFD:
- The second level of decomposition of each process in the 1-level DFD.
- This level represents a more detailed view of the sub-processes identified in the 1-level DFD.
- The sub-processes are decomposed further into smaller sub-processes or activities.
- The data stores and data flow for each sub-process/activity are also identified at this level.
Advanatages of DFDs
- DFD provides an in-depth understanding of a system’s operations and limitations.
- DFDs can be comprehended by both technical and non-technical people because of their easy-to-understand nature.
- DFD offers a detailed and well-explained representation of system components.
- It is used as a part of system documentation files.
- It is a graphical representation that is easy to understand and helps in visualizing system contents.
Disadvantages of DFDs
- DFDs can sometimes be confusing to programmers and other stakeholders, leading to misunderstandings about the system.
- DFD may not capture all the details of a complex system and can oversimplify it, leading to an incomplete or inaccurate understanding of the system.
- The process of creating a DFD can be time-consuming, which may lead to resistance from analysts and other team members.
- Changes made to the system can make the DFD quickly outdated, making it difficult to keep it updated and maintain its relevance.
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