In Gane & Sarson notation, external entity is represented by

Question

BlackTom AI · Accepted Answer

External entities in data flow modeling are shown as simple 2D squares in the Gane & Sarson notation.

1. Relevant knowledge points and concepts
- Data Flow Diagrams (DFDs) model system boundaries, processes, data stores, data flows, and external entities (sources or sinks of data).
- Gane & Sarson is one standard DFD notation; it uses specific shapes to distinguish elements clearly: external entities (sources/sinks) are squares, processes are rounded rectangles, data stores use open-ended rectangles or paired lines, and arrows show data flows.

2. Step-by-step reasoning process
- Identify the element asked about: “external entity” (an actor outside the system that provides or receives data).
- Recall the Gane & Sarson visual conventions: the designers chose a simple square to represent anything outside the system boundary so it’s visually distinct and easy to label.
- Compare the given options to the established conventions: determine which shape matches the convention for external entities.

3. Calculations / intermediate steps
- No numeric calculation is required. The “intermediate steps” are matching the concept (external entity) to the standard symbol in the Gane & Sarson palette: external entity → square.

4. Why the correct answer is correct
- The 2D square is the conventional and documented symbol for external entities in the Gane & Sarson DFD notation because it plainly indicates an outside actor/source/sink and contrasts with the rounded shapes used for internal processes.

5. Why the other options are incorrect
- B. Circle: In some DFD traditions (older Yourdon/DeMarco style), circles or bubbles represent processes, not external entities.
- C. Cuboid: Not a recognized standard symbol in Gane & Sarson; cuboids are not used to denote external entities.
- D. Rounded rectangle: In Gane & Sarson this shape is reserved for processes (internal functional transformations), not external entities.

6. Conclusion
The correct symbol for an external entity in Gane & Sarson notation is a 2D square, which matches option A.

In Gane & Sarson notation, external entity is represented by单项选择题

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