Data flow diagrams

Question 1

What is a data flow diagram?
How is it used to show the flow of information?
Level 0 DFD?
Level 1 DFD?

Answer 1

• A map out the flow of information for any process or system.
• Used to model how data flows through a system. Mainly between external entities to process to data stores.
• Context diagrams, shows data system in limited detail, shows overall flow of data through the whole system
• Focus on one part of the system, gaining a wider range of detail compared to level 0.

Question 2

What is a external entities ?

How is it used to show the flow of information?

Answer 2

• Eternal sources which is communicating with the system.
• Refers to an outside systems which sends and receive data.
• School reports: input info about a student is entering, and then the report it’s sent to parents, leaving the system. External entity = storing that report somewhere.

Question 3

What is a processes?

How is it used to show the flow of information?

Answer 3

• Anything that happens to modify the data, results an output being produced by the system.
• Perform a calculation, sort data, or direct data flow based on business rules.
• Every process must consist of one input and output to gain results.
• School report: once teacher input comments, the process will combine all comments to form a final report for all subjects. Then is distributed to parents.

Question 4

What is a data stores?

How is it used to show the flow of information?

Answer 4

• Files which hold information, because it needs to be used at a later time or date.
• Represents any real world sort of data held in the system.
• E.g: database table, database form

Question 5

What is a data flow?

Answer 5

• Flows of data between the entities – processes – data stores
• Route data takes between all the three above.
• How does your data move around the system.

Question 6

What is a standard symbols?

Answer 6

• External entity = oval OR oval with chord line showing a duplicate.
• Process = rectangle with a horizontal line a third down. From horizontal line, 1/4 way across, vertical line up.
• Data flow = line with arrow shows direction.
• Data store = slim rectangle with vertical line 1/4 across.

Question 7

What is a connectivity rules for drawing Level 1 DFSs?

How is it used to show the flow of information?

Answer 7

• Highlights the main functions carried out by the systems
• Breaks down the high-level process of context diagram to sub-process.
• Every process must consist of one input and output to gain results. Each entity is submitting or receiving date.
• Data has to flow in ONE direction. Each form has its own arrow and label, and MUST have this.
• Arrow and labels highlight the direction of the data, and what type of data is travelling.
• Every data flow has to link to one process. Data is either going to a data store after it is processed OR coming from a data store ready to be processed.
• One input of data and one output of data flow required for each process.

Question 8

Impacts affecting the flow of information in information systems

Answer 8

• Information characteristics: If the info is poor quality it’s going to impact your results. Examples good quality, accurate.
• Hardware: system failure: delay in flow of info, OR lack of storage: info not saved correctly.
• Human error: could result in data being incomplete OR lost
• Delays: due to lack of communication.