Data Flow Diagram EXAMPLE [How to Create Data Flow Diagrams]

Summary

This tutorial provides a comprehensive guide to Data Flow Diagrams (DFDs), explaining their purpose, components, and how to create them. It covers key notations like Yourdon & DeMarco and Gane & Sarson, and outlines the different levels of DFDs—from Context to Level 2. Through a case study of Amazon's purchasing system, the tutorial demonstrates the practical application of DFDs. The video also delves into best practices and rules for creating clear and effective DFDs, such as ensuring proper data flow and process interactions. It also contrasts logical and physical DFDs, emphasizing their respective roles in business analysis and system design.

Takeaways

• 😀 DFDs are visual models that represent the flow of data through a system, showing where data comes from, how it is transformed, stored, and used.
• 😀 Common DFD notations include Yourdon & DeMarco, SSADM, and Gane & Sarson, each with slight differences in how components like processes and data stores are represented.
• 😀 The main components of a DFD are external entities, processes, data stores, and data flows, all of which play a vital role in illustrating how a system operates.
• 😀 External entities can be sources (providing data) or sinks (receiving data), and they are typically labeled with nouns (e.g., *Customer*).
• 😀 A process in a DFD is an activity that transforms data, labeled with an active verb-noun format (e.g., *Order Item*), and must have both input and output data flows.
• 😀 Data stores represent repositories for data at rest and must have input and output data flows. Labels for data stores should also follow a noun phrase (e.g., *Order Details*).
• 😀 Data flows represent the movement of data between entities, processes, and data stores, and should be labeled with nouns (e.g., *Sales Order*).
• 😀 DFDs are organized into different levels, from the highest-level context diagram (Level 0) to more detailed diagrams (Level 1, Level 2) that break down processes further.
• 😀 The Level 0 diagram represents the general system and includes one process node, representing the entire system with inputs and outputs from external entities.
• 😀 Level 1 and Level 2 diagrams decompose processes into smaller sub-processes, with reference numbers like 1.1, 1.2, and 2.1 to show the hierarchy and sequence.
• 😀 Best practices for DFDs include maintaining balance between levels, avoiding excessive complexity (e.g., no more than 12 processes), and ensuring all processes are linked to at least one data store or process.

Q & A

What is the primary purpose of a data flow diagram (DFD)?

A data flow diagram (DFD) is used to visually represent the flow of data through a system. It illustrates how data enters and exits a system, what activities transform the data, and where the data is stored or utilized.

What are the main components of a DFD?

The main components of a DFD include external entities, processes, data stores, and data flows. External entities interact with the system, processes transform data, data stores hold data at rest, and data flows represent the movement of data.

What are the common notations used in data flow diagrams?

Common notations for DFDs include rectangles for external entities, ovals or circles for processes, and lines with arrows for data flows. Data stores are represented differently depending on the notation, such as parallel horizontal lines (DeMarco) or open-ended rectangles (Yourdon).

How do external entities function in a DFD?

External entities are outside objects (like people, organizations, or other systems) that interact with the system. They can be classified as sources (providing data to a process) or sinks (receiving data from a process). An entity can also act as both a source and a sink.

What is the significance of reference numbers in DFDs?

Reference numbers help indicate the level of detail in a DFD. For example, a process labeled '1.0' represents the first process at Level 0, while '1.1' or '1.2' would represent sub-processes at Level 1. These numbers maintain clarity as the diagram decomposes into further levels.

What are the different levels of a DFD, and what do they represent?

The different levels of a DFD include: - Level 0 (Context Diagram): Shows the system boundary with one process node and key external entities. - Level 1: Decomposes the system into primary processes and their interactions with data stores and entities. - Level 2: Decomposes the processes from Level 1 into more detailed activities. Further levels are possible, but typically no more than Level 3 is used.

What are some key rules for creating a data flow diagram?

Key DFD rules include: - Data must not flow directly between two entities. - Data must flow from a process to an entity or from an entity to a process. - A process must have both input and output data flows. - Data stores must have both input and output data flows. - Keep the number of processes manageable (preferably no more than 12).

What is the difference between logical and physical data flow diagrams?

A logical DFD focuses on what happens to the data from a business perspective, illustrating processes and goals. A physical DFD shows how the system is implemented, including how data moves through physical elements like databases, forms, and systems.

What does it mean for a DFD to be 'balanced'?

A balanced DFD maintains consistency between different levels. For example, the input and output data flows of a higher-level process should be preserved when the process is decomposed into sub-processes at a lower level, ensuring that the diagram accurately reflects the system's flow of data.

Can you give an example of a DFD in a real-world application?

An example is the Amazon product purchase system. In the Level 0 diagram, the primary process is 'purchase product' with external entities like the customer, vendor, and financial institution. Data flows include customer credentials, product queries, inventory checks, and payment processing. The Level 1 diagram further breaks down the checkout process into sub-processes like entering shipping details, choosing a payment method, and checking funds availability.