What is the basic differences among data dictionary entries prepared for data stores, data structures, and data elements?
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Data dictionary entries may be created after the data flow diagram has been completed, or they may be constructed as the data flow diagram is being developed. The use of algebraic notation and structural records allows the analyst to develop the data dictionary and the data flow diagrams using a top-down approach. For instance, the analyst may create a Diagram 0 data flow after the first few interviews and, at the same time, make the preliminary data dictionary entries. Typically, these entries consist of the data flow names found on the data flow diagram and their corresponding data structures.
After conducting several additional interviews with users to learn the details of the system and the ways they interact with it, the analyst will expand the data flow diagram and create the child diagrams. The data dictionary is then modified to include the new structural records and elements gleaned from further interviews, observation, and document analysis.
Each level of a data flow diagram should use data appropriate for the level. Diagram 0 should include only forms, screens, reports, and records. As child diagrams are created, the data flow into and out of the processes becomes more and more detailed, including structural records and elements.
Figure below illustrates a portion of two data flow diagram levels and corresponding data dictionary entries for producing an employee paycheck. Process 5, found on Diagram 0, is an overview of the production of an EMPLOYEE PAYCHECK. The corresponding data dictionary entry for EMPLOYEE RECORD shows the EMPLOYEE NUMBER and four structural records, the view of the data obtained early in the analysis. Similarly, TIMEFILE RECORD and the EMPLOYEE PAYCHECK are also defined as a series of structures.
Two data flow diagrams and corresponding data dictionary entries for producing an employee paycheck.
It is important that the data flow names on the child data flow diagram are contained as elements or structural records in the data flow on the parent process. Returning to the example, WAGE INFORMATION (input into process 5.3, COMPUTE CURRENT PAYAMOUNTS) is a structural record contained in the EMPLOYEE RECORD (input to process 5). Similarly, GROSS PAY(output from process 5.3.4, a lower-level process not shown in the figure) is contained in the structural record CURRENT PAYAMOUNTS (output from the parent process 5.3, COMPUTE CURRENT PAYAMOUNTS).
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Data science is an inter-disciplinary field that uses scientific methods, processes, algorithms and systems to extract knowledge and insights from many structural and unstructured data. Data science is related to data mining, machine learning and big data
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