Demand analysis, that is, the identification and division of system functions, and uses this identification and division using DFD models, and finally describes, record, and aggregate data and processing in DFD with data dictionary.
This document is recorded in the process of learning and practicing system functionality.
1. Division principle
The basic idea of functional division should of course be "self-top, gradually refined", which is probably has become a non-porous classic classic in software engineering. Starting from the CONTEXT DIAGRAM, gradually subdivided into a grade flow map, two flow maps, etc. Function (Note 1). Different levels of data flow diagrams are a coverage of the overall or part of the system, and the larger the overlay, the larger the overlay, the larger the overlay.
Note 1: The original text "Software Engineering - Practitioner 's Research Method 5" P236.
It is necessary to pay attention to the continuity of data streams between different subdivision levels during subdivision or refining. That is, how many layers are subdivided to a processing, and the data flow flowing and flowing out of the processing should be maintained.
By the way, "consistency" is a habit of analytical personnel should always pay attention to maintaining in the demand analysis. Includes consistency, DFD and data dictionary, and so on. This requires other modifications to other relevant aspects while modifying some of the contents in the model.
