1. There are four components to a data flow graph:
source or destination;
deal with;
data;
data flow.
When drawing a data flow diagram, you should first divide the components.
Second, the function decomposition:
When further decomposition will involve how to specifically implement a function, it should not continue to be decomposed.
Continuity of information must be maintained during hierarchical refinement. That is, when a process is decomposed into a series of processes, the input and output data streams before and after decomposition must be the same. ,
3. Naming
1. Data flow
1) The name should represent the content of the entire data stream, not just some of its components;
2) Avoid the use of empty names that lack specific meaning ("data", "information", "input", etc.);
3) If there is difficulty in naming a data flow, it may be caused by improper decomposition of the data flow graph, and you should try to decompose it again.
2. Handling
1) Name the data stream first, and then name the processing associated with it;
2) The name should reflect the function of the entire process, not part of it;
3) The name is best composed of a specific transitive verb plus a specific object (verb-object phrase, such as "update list", "generate report"), try to avoid the use of "processing", "processing" and other empty and general verb as name
4) Usually the name contains only one verb. If two verbs must be used to describe accurately, it should be considered to be divided into two processes;
5) When there is difficulty in naming, it may be caused by improper decomposition.
Fourth, the role of data flow diagrams
1. The basic function of drawing a data flow diagram is to use it as a function of communicating information;
2. As a tool for analysis and design.
Five, some online pictures
