Database Design-Data Flow Diagram (DFD) and data flow dfd

Database Design-Data Flow Diagram (DFD) and data flow dfd
1. Data Flow Diagram definition data flow diagram (DFD) is a tool used in structural analysis. It graphically depicts the process of data flow and processing in the system, because it only reflects the logical functions required by the system, it is a function model. In structured development, data flow graphs are the results of the demand analysis phase. ---- Baidu encyclopedia

2. How to use a data flow chart

A Data Flow Chart uses a layered form to describe the flow of system data. Each layer represents the flow of system data.

The higher the level, the more abstract the data flow. High-level DFD graph processing can be performed in one

The steps are decomposed into low-level and more detailed DFD diagrams.

2.1 Data Flow Graph Representation (Gane-Sarson Model)

2.2 Definitions of various graphs in the Data Flow Graph Representation Method

Data source points and data collection points: persons or things outside the system that are connected to the system.

Used to express the external source and destination of the system data.

Data Flow: indicates the input or output of the processing function. Arrows indicate the data flow.

Processing or processing: Refers to processing and transforming data.

Data storage: A logical term used to store data in a living environment. It is generally a table structure.

2.3 layered structure of a data flow chart

2.4 Data Flow Graph instance

Top-layer data flow chart

First layer data flow diagram

Layer 2 Data Flow Diagram-1

Layer 2 Data Flow Diagram-2

Layer 2 Data Flow Diagram-3

Layer 2 Data Flow Diagram-4

3. Note: 3.1 The hierarchy should follow the principle (1) All the processing processes on the same graph should be at the same abstraction level. (2) A processing process is expanded, which is generally divided into 4 ~ 10 are recommended. 3.2 correctness check (1) Data conservation, it is also called matching of input and output data. ① if processing has input, there should be output. ② If processing has output, there must be input. ③ all input data should flow out of the processing or be used to generate the output data. data (excluding useless data) ④ All output data must have been imported into the processing or generated by the data processing that flows into the processing (ensure necessary data)
(2) Any data storage in a data flow diagram must have inbound and outbound data streams. (3) the input and output data streams processed in a parent graph must appear in the corresponding subgraph.
3.3 improve ease of use (1) Simplify the relationship between Processing (using data storage) Example: Set P1, P2 as processing, D1 as data storage P1-> P2 can be changed: p1-> D1 D1-> P2 (2) Uniform decomposition (3) appropriate name
3.4 determine system boundaries (1) exclude Manual Activities (2) exclude activities of other external systems (3) interface between external source points outside the system through data flow

Copyright Disclaimer: This article is an original article by the blogger and cannot be reproduced without the permission of the blogger.