A logical data flow diagram (DFD) is a visual representation that illustrates the flow of data within a system, emphasizing what happens rather than how it happens. In essence, it maps out the business events and the data involved in each.
Key Aspects of a Logical DFD
Here's a breakdown of what constitutes a logical DFD:
- Focus on Business Events: It describes the core activities or events that take place within a system. Examples include:
- Placing an order.
- Processing a payment.
- Adding a new customer.
- Data Requirements: It specifies the data necessary for each of these events to occur. Examples include:
- Customer details (name, address, contact information).
- Order information (items, quantities, price).
- Payment information (card details, billing address).
- Abstraction of Implementation: It does not depict the physical implementation or technology used. It avoids details about databases, software, or specific hardware. It is focused on the data flow related to each business process/event.
- Foundation for Physical DFD: According to the reference, the logical DFD serves as a solid base for creating a physical DFD. This means it sets the stage for mapping how the actual system will be designed, including technology and resources.
Differences between Logical and Physical DFD
| Feature | Logical DFD | Physical DFD |
|---|---|---|
| Focus | Business events and data requirements | Hardware, software, files, and people involved |
| Abstraction | High level, implementation details omitted | Low level, specific implementation details included |
| Purpose | Understand what needs to happen | Understand how it happens |
| Technology | Independent of technology | Dependent on specific technology |
Example Scenario
Let's consider a simple online book store:
- Logical DFD Example Event: A customer places an order.
- Required Data: This event requires:
- Customer information (name, shipping address).
- Book selection (title, quantity).
- Payment details (credit card information).
A logical DFD would show the flow of these data items and their association with the "Place Order" business event.
Importance of Logical DFD
- Clear understanding: Helps stakeholders comprehend the system from a business perspective.
- Basis for design: Provides a foundation for the physical design and system development.
- Communication tool: Facilitates communication among business users, analysts, and developers.
- Reduced ambiguity: By clarifying the required data and process, the overall system specification is less ambiguous.
In summary, a logical data flow diagram is an essential tool for defining and understanding the flow of data in a system, focusing solely on business events and their associated data requirements, setting the stage for a subsequent physical implementation design. It does not get into the implementation, but rather focuses on the business process and its related data.
