Data Flow Diagram
Micah Pate 20 Jun 2013 CIS3512/5197
Assignment 6
Pg 305 2. What is a data flow diagram? Why do systems analysts use data flow diagrams? Answers: A picture of the movement of data between external entities and the processes and data stores within a system. Systems analysts use DFDs to help in the analysis phase by accomplishing the following three things: 1. Requirements Determination 2. Requirements Structuring 3. Alternative Generation and Selection 3. Explain the rules for drawing good data flow diagrams. Answers: Process: A. No process can have only outputs. It is making data from nothing (a miracle). If an object has only outputs, then it must be a source. B. No process can have only inputs (a black hole). If an object has only inputs, then it must be a sink. C. A process has a verb phrase label. Data Store: D. Data cannot move directly from one data store to another data store. Data must be moved by a process. E. Data cannot move directly from an outside source to a data store. Data must be moved by a process which receives data from the source and places the data into the data store. F. Data cannot move directly to an outside sink from a data store. Data must be moved by a process. G. A data store has a noun phrase label. Source/Sink: H. Data cannot move directly from a source to a sink. It must be moved by a process if the data are of any concern to our system. Otherwise, the data is not shown in the DFD. I. A source/sink has a noun phrase label.
Data Flow: J. A data flow has only one direction of flow between symbols. It may flow in both directions between a process and a data store to show a read before an update. The latter is usually indicated, however, by two separate arrows since these happen at different times. K. A fork in a data flow means that exactly the same data goes from a common location to two or more different processes, data stores, or sources/sinks (this usually indicates different copies of the same data going to different
Assignment 6
Pg 305 2. What is a data flow diagram? Why do systems analysts use data flow diagrams? Answers: A picture of the movement of data between external entities and the processes and data stores within a system. Systems analysts use DFDs to help in the analysis phase by accomplishing the following three things: 1. Requirements Determination 2. Requirements Structuring 3. Alternative Generation and Selection 3. Explain the rules for drawing good data flow diagrams. Answers: Process: A. No process can have only outputs. It is making data from nothing (a miracle). If an object has only outputs, then it must be a source. B. No process can have only inputs (a black hole). If an object has only inputs, then it must be a sink. C. A process has a verb phrase label. Data Store: D. Data cannot move directly from one data store to another data store. Data must be moved by a process. E. Data cannot move directly from an outside source to a data store. Data must be moved by a process which receives data from the source and places the data into the data store. F. Data cannot move directly to an outside sink from a data store. Data must be moved by a process. G. A data store has a noun phrase label. Source/Sink: H. Data cannot move directly from a source to a sink. It must be moved by a process if the data are of any concern to our system. Otherwise, the data is not shown in the DFD. I. A source/sink has a noun phrase label.
Data Flow: J. A data flow has only one direction of flow between symbols. It may flow in both directions between a process and a data store to show a read before an update. The latter is usually indicated, however, by two separate arrows since these happen at different times. K. A fork in a data flow means that exactly the same data goes from a common location to two or more different processes, data stores, or sources/sinks (this usually indicates different copies of the same data going to different