Question Details

MGMT 340 Week 3 Data Flow Diagramming

Data-Flow Diagramming

Data-flow diagrams use four symbols.
1.	Symbols that represent how data flows
2.	Symbols that describe where data is temporarily stored
3.	Symbols that show the processes to modify data
4.	Symbols that show source/sinks which are external data in-flows and out-flow
Symbol	Definition	Representation	Examples
Data Flow	Depicts data moving in a system and moves the data as a whole	Arrow	Database searches, marketing reports, and product orders
Data Store	Describes where data is temporarily stored	Rectangle with its right vertical line missing	A filing cabinet, notebook, or a database
Business Process	Represents the actions performed on data to transform it into information or new knowledge	Rectangle with rounded corners	N/A
Sources/Sinks	Sources are the external origin of data coming into our system.
Sinks are the destination of data our system creates and disseminates externally.	Rectangles	Suppliers are examples of sources, and customers are examples of sinks.
Analysts are not concerned with the interactions between sinks and sources, how a source gets the data it sends to our system, or what the sink does with information our system sends it.
Symbol	Comparison of Symbols
Data Flow	A data flow depicts data moving in a system and moves the data as a whole. An arrow is used to depict a data flow on a DFD. Database searches, marketing reports, and product orders are good examples of data flows.
Data Store	In contrast to a data flow (data in motion), a data store represents data at rest. A data store is depicted as a rectangle with its right vertical line missing on data-flow diagrams. A filing cabinet, notebook, or a database are data stores.
Business Process	A business process is depicted as a rectangle with rounded corners, and represents the actions performed on data to transform it into information or new knowledge.
Sources/Sinks	Sources are the external origin of data coming into our system, and sinks are the destination of data our system creates and disseminates externally. Sources and sinks are depicted on DFDs as rectangles. Suppliers are examples of sources, and customers are examples of sinks. Analysts are not concerned with the interactions between sinks and sources, how a source gets the data it sends to our system, or what the sink does with information our system sends it.
Here is a graphical representation of what the four symbols look like. Move your mouse pointer over them to review definitions, descriptions, and examples of use.
The Flow of Data
 

Transcript
The scope of a system is depicted by a context diagram, which shows the system- interactions with sources and sinks. The context diagram has only one process (that represents the entire system) labeled “0,” and no data stores. Once the context diagram is completed, a level-0 diagram is prepared. The level-0 diagram depicts the key system processes, data flows, and data stores.
The figure below depicts a Context Diagram.
A Context Diagram of Hoosier Burger's Food-Ordering System
 
Transcript
The figure below depicts a Level-0 Diagram.
Dynamic Flow Diagram
 
Transcript
A set of rules describes how the data-flow diagram is prepared. The inputs to a process must be different from the outputs, and all objects must have unique labels. The context diagram is further broken down (decomposed) into a series of sub-processes resulting in the creation of multiple levels of diagrams. Decomposition continues until a sub-process cannot be broken down into more detail, and is called a Primitive DFD.
•	A balanced DFD is one where the data inputs and data outputs are the same at the next level.
•	Completeness means all required components on a DFD are drawn and documented.
•	DFD consistency means all information on one level is also included on other levels.
•	Time is not represented on DFDs. They do not show how often an activity occurs.
•	The systems analyst has reached the primitive level when processes cannot be broken down any further.
This nested decomposition is referred to as a level-n diagram.
Creating DFDs is like prototyping; the systems analyst reviews each iteration with the users, then modifies the DFDs for further review until the users agree that the business processes are captured correctly.
DFDs can be used to perform gap analysis between the existing system and the proposed system and for displaying inefficiencies in the business operation.