Data Flow Diagram

Drawing the system DFD diagram is a very important part in the requirement analysis of building the system. Today, we will give a brief overview of the data flow graph section.

Composition:

A data flow chart is represented by four types of symbols. They are:Processing,Data Stream,Data storage files,Data SourceOrSettlement point.

Data Flow diagram design principles:

~From outside to inside, from top to bottom, refined layer by layer, and gradually refined;

~Maintain the balance between the parent and subgraphs. The input and output data streams in the parent graph must be consistent with those in the subgraphs;

~Maintain data conservation. The data in all output data streams of a processing operation must be directly obtained from the processed input data streams,Each process must have an input data stream and an output data stream.. The output data stream is determined only by the input data stream.Any data stream must be processed.

No data flow exists between the external entity and the external entity.;

Data Streams cannot exist between external entities and data storage.;

Data Streams cannot exist between data storage and data storage.;

A data stream in the parent graph may be obtained by combining multiple data streams in the subgraph. Therefore, there is often a relationship between data streams:

~Hidden processing details;

~Simplify the relationship between processes. The call for High Cohesion and low coupling.

~Uniform decomposition. Make sure that each processing layer is roughly the same.

~Proper status data stream, processing, file, source/fate name, the name should reflect the actual meaning of this component, avoid empty name;

~Ignore the branches;

~Arrows represent data streams rather than control flows.The flow chart contains the control flow..

Data Dictionary

On the basis of a data flow chart, you need to describe each data flow, file, and data item. In this case, you need to use the data dictionary.

This section describes the composition and Design Principles of the data flow diagram and the data dictionary method. Are a simple overview, the specific practices in reference to this article, do a few questions will be more clear.