Data Flow Diagram Guidelines Flashcard

What must be true about the input and output of a process in a DFD?

The input to a process must be different from the output of that process.

Why must every process have a unique name in a DFD?

A process name should clearly describe its function to avoid confusion and ensure accurate documentation.

Can a process have only outputs?

No. If an object has only outputs, it must be a source, not a process.

Can a process have only inputs?

No. If an object has only inputs, it must be a sink, not a process.

How is a process labeled in a DFD?

A process is labeled using a verb phrase (e.g., 'Process Order').

Can data move directly from one data store to another in a DFD?

No. Data must be moved by a process.

Can data move directly from an outside source to a data store?

No. Data must be moved by a process.

Can data move directly from a data store to an outside sink?

No. Data must be moved by a process.

How is a data store labeled?

A data store has a noun phrase label (e.g., 'Customer Database').

Can data move directly from a source to a sink?

No. It must be moved by a process if the data is relevant to the system; otherwise, it is not shown on the DFD.

How is a source/sink labeled?

A source or sink is labeled with a noun phrase (e.g., 'Supplier').

How does data flow direction work in a DFD?

Data flows in only one direction between symbols. For actions like 'read before update,' use two separate arrows to indicate different timings.

What does a fork in data flow indicate?

A fork means the same data is sent from a common point to multiple processes, data stores, or sources/sinks, indicating copies of data going to different locations.

What does a join in data flow mean?

A join means identical data is received at a common location from multiple sources (processes, data stores, or external entities).

Can data flow directly back to the process it originated from?

No. At least one intermediary process must handle the flow before it loops back.

What does a data flow to a data store represent?

It represents an update (delete or change).

What does a data flow from a data store represent?

It represents a retrieval or use of data.

How is a data flow labeled?

A data flow should have a noun phrase label. Multiple noun phrases can appear on one arrow if they move together as a single unit.

How does time work in DFDs?

Time is not well-represented in DFDs. It is best to treat DFDs as perpetual systems with no defined start or stop points.

How should DFD development be approached?

DFD development is iterative. Expect to redraw diagrams multiple times to achieve the closest approximation of the system.