With reference to assignments 8 and 9, what characteristics does an analyst(you) examine when evalauating DFD quality?
According to my research, Data-flow diagram (DFD) is a graphical representation of the "flow" of data through an information system. DFDs can also be used for the visualization of data processing (structured design). On a DFD, data items flow from an external data source or an internal data store to an internal data store or an external data sink, via an internal process.
A DFD provides no information about the timing of processes, or about whether processes will operate in sequence or in parallel. It is therefore quite different from a flowchart, which shows the flow of control through an algorithm, allowing a reader to determine what operations will be performed, in what order, and under what circumstances, but not what kinds of data will be input to and output from the system, nor where the data will come from and go to, nor where the data will be stored (all of which are shown on a DFD).
A DFD provides no information about the timing of processes, or about whether processes will operate in sequence or in parallel. It is therefore quite different from a flowchart, which shows the flow of control through an algorithm, allowing a reader to determine what operations will be performed, in what order, and under what circumstances, but not what kinds of data will be input to and output from the system, nor where the data will come from and go to, nor where the data will be stored (all of which are shown on a DFD).
Characteristics Examined in Evaluating Data Flow Diagram:
Balancing of data flows
The concept of balancing states that all the incoming flows to a process and all the outgoing flows from a process in the parent diagram should be preserved at the next level of decomposition. Process decomposition lets you organize your overall DFD in a series of levels so that each level provides successively more detail about a portion of the level above it. The goal of the balancing feature is to check your system internal consistency, which is particularly useful as different levels of expertise are generally involved in a project. When you decompose a process, PowerDesigner helps you initialize, in the sub diagram, the objects from the upper-level to link to the sub-process. PowerDesigner automatically retrieves global objects, such as external entities or data stores and creates object shortcuts, if need be. A data flow diagram illustrates the processes, data stores, and external entities in a business or other system and the data flows between these things. Four diagramatical components are used to develop a DFD.
Leveling of Data Flow Diagram
All data flows entering and leaving a process must appear on the corresponding diagram which decomposes that process.
The access to data stores across levels of diagrams must be consistent:
• the direction of accesses must match and all accesses on higher level diagrams must appear on corresponding lower level diagrams
• a data store is first shown on the highest level diagram where it is accessed by more than one process
• it can then appear on all lower level diagrams where it is accessed
Develop a Physical Data Flow Diagram
Most logical design level TPS structured design is data flow diagram (DFD) based, since typically the data is simple in structure and independent from the procedural modules because of the need for sharing of data between applications. Complex entity relationship diagrams (ERD) based design methods are therefore seldom required for TPS systems. At the physical design level however, no predominate structured design approach has appeared.
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