Logical DFD vs. Physical DFD

Attribute	Logical DFD	Physical DFD
Representation	Abstract representation of the system's processes and data flows	Physical representation of the system's processes and data flows
Focus	Focuses on the system's functionality and requirements	Focuses on the system's implementation and technology
Level of Detail	High-level view of the system's processes and data flows	Detailed view of the system's processes and data flows
Abstraction	Abstracts away the implementation details	Includes implementation details
Notation	Uses symbols like circles, arrows, and rectangles	Uses symbols like circles, arrows, and rectangles
Focus on Data	Emphasizes the flow of data between processes	Emphasizes the physical storage and movement of data
Focus on Processes	Emphasizes the logical processes and transformations	Emphasizes the physical processes and operations
Implementation Independence	Independent of any specific technology or implementation	Dependent on the chosen technology and implementation

Introduction

Data Flow Diagrams (DFDs) are powerful tools used in system analysis and design to represent the flow of data within a system. They provide a visual representation of how data moves through processes, data stores, and external entities. DFDs are commonly used in both logical and physical system modeling. In this article, we will compare the attributes of Logical DFDs and Physical DFDs, highlighting their differences and similarities.

Logical DFD

A Logical DFD focuses on the logical aspects of a system, abstracting away the physical implementation details. It represents the system's functionality and the flow of data between processes, data stores, and external entities. The primary goal of a Logical DFD is to understand the system's requirements and provide a high-level view of the system's processes and data flows.

Logical DFDs are often used during the early stages of system analysis and design to capture the essential functions and data requirements of the system. They are typically represented using standardized symbols, such as circles for processes, arrows for data flows, and rectangles for data stores and external entities.

One of the key attributes of a Logical DFD is its simplicity. It focuses on the "what" rather than the "how" of the system. It abstracts away the implementation details, such as hardware, software, and network configurations, allowing analysts to focus on understanding the system's requirements and functionality.

Another attribute of a Logical DFD is its ability to provide a clear and concise representation of the system's processes and data flows. By removing unnecessary details, it allows analysts to communicate the system's functionality to stakeholders in a more understandable and meaningful way. This helps in identifying potential issues, improving system understanding, and facilitating effective decision-making.

Logical DFDs are also highly flexible and can be easily modified and refined during the system analysis and design process. They provide a foundation for further development and serve as a basis for creating Physical DFDs.

Physical DFD

A Physical DFD, on the other hand, focuses on the physical implementation of the system. It represents the actual hardware, software, and network configurations required to support the system's functionality. Physical DFDs provide a detailed view of how data flows through the system, including the specific data stores, files, and databases used.

Physical DFDs are typically created after the Logical DFDs have been developed and serve as a bridge between the logical and physical aspects of the system. They provide a more detailed representation of the system's processes, data flows, and data stores, taking into account the specific technologies and resources used in the system's implementation.

One of the key attributes of a Physical DFD is its focus on the "how" of the system. It includes specific details about the hardware, software, and network components required to support the system's functionality. This level of detail helps in understanding the system's technical requirements and constraints.

Physical DFDs also provide a more accurate representation of the system's data flows. They include specific data stores, files, and databases used in the system, allowing analysts to identify potential bottlenecks, data redundancies, and performance issues. This level of detail is crucial for system implementation and optimization.

Another attribute of a Physical DFD is its ability to support system documentation and implementation. It provides a detailed blueprint for system developers, allowing them to understand the system's requirements and design. Physical DFDs can also be used to generate code, configure databases, and set up network connections, making the implementation process more efficient and accurate.

Comparison

While Logical DFDs and Physical DFDs have distinct attributes, they are closely related and serve different purposes in the system analysis and design process. Let's compare their attributes:

1. Focus

Logical DFDs focus on the system's functionality and requirements, abstracting away the physical implementation details. They provide a high-level view of the system's processes and data flows. Physical DFDs, on the other hand, focus on the physical implementation of the system, including the specific hardware, software, and network configurations required.

2. Level of Detail

Logical DFDs provide a simplified and abstracted view of the system, removing unnecessary details. They focus on the essential functions and data flows. Physical DFDs, on the other hand, provide a more detailed view of the system, including specific data stores, files, and databases used. They include the necessary technical details for system implementation.

3. Representation

Logical DFDs are typically represented using standardized symbols, such as circles for processes, arrows for data flows, and rectangles for data stores and external entities. They provide a clear and concise representation of the system's functionality. Physical DFDs, on the other hand, include specific hardware, software, and network components, represented using appropriate symbols. They provide a more detailed and accurate representation of the system's implementation.

4. Purpose

Logical DFDs are primarily used to understand the system's requirements, functionality, and high-level processes. They help in identifying potential issues, improving system understanding, and facilitating effective decision-making. Physical DFDs, on the other hand, are used to bridge the gap between the logical and physical aspects of the system. They provide a detailed blueprint for system implementation, optimization, and documentation.

5. Flexibility

Logical DFDs are highly flexible and can be easily modified and refined during the system analysis and design process. They provide a foundation for further development and serve as a basis for creating Physical DFDs. Physical DFDs, on the other hand, are less flexible as they represent the specific implementation details of the system. Changes in the physical implementation may require modifications to the Physical DFD.

Conclusion

Logical DFDs and Physical DFDs are both valuable tools in system analysis and design. While Logical DFDs focus on the system's functionality and requirements, Physical DFDs provide a detailed view of the system's physical implementation. Logical DFDs help in understanding the system's high-level processes and facilitating effective decision-making, while Physical DFDs bridge the gap between the logical and physical aspects of the system, providing a blueprint for system implementation and optimization. Both types of DFDs have their unique attributes and serve different purposes in the system development lifecycle.