Data flow diagrams Flashcards

1
Q

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

A
  • 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.
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2
Q

What is a external entities ?

How is it used to show the flow of information?

A
  • 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.
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3
Q

What is a processes?

How is it used to show the flow of information?

A
  • 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.
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4
Q

What is a data stores?

How is it used to show the flow of information?

A
  • 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
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5
Q

What is a standard symbols?

A
  • 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
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6
Q

What is a connectivity rules for drawing Level 1 DFSs?

How is it used to show the flow of information?

A
  • 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.
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7
Q

Impacts affecting the flow of information in information systems

A
  • 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.
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