- Describe the Gane and Sarson symbols used for processes, data flows, data stores, and entities. Give four examples of typical names for processes, data flows, data stores, and entities.
- What is the relationship between a context diagram and diagram 0, and which symbol is not used in a context diagram?
The Correct Answer and Explanation is :
1. Gane and Sarson Symbols
In Gane and Sarson’s data flow diagram (DFD) methodology, the symbols represent key elements such as processes, data flows, data stores, and entities.
- Process: Represented by a rectangle with rounded corners. A process shows how data is transformed or manipulated. It is always labeled with a verb-noun phrase to indicate the action or operation taking place.
- Examples of process names:
- “Process Order”
- “Validate Payment”
- “Generate Report”
- “Check Stock Availability”
- Examples of process names:
- Data Flow: Represented by an arrow. Data flows show the direction in which data moves from one part of the system to another, either between processes, data stores, or entities. They are named using nouns to describe the data being transferred.
- Examples of data flow names:
- “Order Information”
- “Payment Details”
- “Customer Data”
- “Invoice”
- Examples of data flow names:
- Data Store: Represented by a rectangle with open sides. A data store represents a place where data is stored within the system for later use or processing.
- Examples of data store names:
- “Customer Database”
- “Order Records”
- “Inventory File”
- “Product Catalog”
- Examples of data store names:
- Entity: Represented by a rectangle. Entities are external agents (people, systems, or organizations) that interact with the system. They are usually sources or destinations of data flows.
- Examples of entity names:
- “Customer”
- “Supplier”
- “Payment Gateway”
- “Sales Representative”
- Examples of entity names:
2. Context Diagram vs. Diagram 0
A context diagram provides a high-level view of a system, illustrating the system as a single process along with external entities and the data flows between them. It shows the system’s boundaries and interaction with external entities, without detailing internal processes.
Diagram 0 (also called “Level 1 DFD”) is a more detailed version of the context diagram. It breaks down the single process from the context diagram into several sub-processes, revealing more information about how the system operates internally. It expands the context diagram’s central process into multiple processes while still maintaining interaction with the same external entities.
Relationship between Context Diagram and Diagram 0:
- A context diagram is essentially the “top-level” DFD and focuses solely on the external interactions, simplifying the system’s representation. It only includes the system as a single process and external entities.
- Diagram 0, on the other hand, begins to show internal processes, breaking down the major process into smaller sub-processes. The entities and the general data flows are the same, but Diagram 0 introduces internal details about how the system functions.
Symbol not used in a Context Diagram:
- Data Stores are not included in the context diagram. Since the context diagram focuses only on the high-level interactions between the system and external entities, it doesn’t delve into internal storage or how data is retained in the system. Data stores are only represented in Diagram 0 and subsequent levels, where the system’s internal workings are detailed.