Answer to Question 1
TRUE
Explanation: 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 because the read and update usually happen at different times.
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Answer to Question 2
File processing systems have several disadvantages, including:
1. Program-data dependenceThe program is tied to the underlying data. Whenever the data changes, (in the sense of structurally), then the program must be modified.
2. Duplication of dataApplications are often developed separately, resulting in duplicate data.
3. Limited data sharingThis is closely related to disadvantage 2, since often applications are developed in a silo. So, for example, the accounting department might develop an application which uses some of the same data as another department. However, there is no data sharing, so two sets of data are maintained.
4. Excessive program maintenance and lengthy development timesSince the programmer has to write all of the low-level file I/O for the application, this adds to the complexity of the application. Also, since the program might need maintenance whenever there is a change to the attributes of the data, there is a need for a lot of program maintenance.
The phosphorus cycle. Numbers are 1012 g P or fluxes as 1012 g P per year (data from Schlesinger 199
The nitrogen cycle. Numbers represent fluxes as 1012 g N per year (data from Schlesinger 1991, after
Cross functional Process Flow Diagram
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