Summary of writing software engineering documents

It took about a week from the beginning to the end. Although I am not sure what to write during the writing process, I want to know what to do from the software engineering documentation. Of course, they have also deepened their understanding of some knowledge points.

The current understanding is far from enough. The summary of the data flow diagram, system flowchart, erdiagram, IPO diagram, and module involved in the document is scattered.

 

1. Data Flow Diagram

A data flow chart, also known as the data flow chart date flowdiworkflow and DFD, is a graphical tool that helps you understand and analyze the data flow of the system, it accurately describes system functions, inputs, outputs, and data storage logically, and is an important part of the system logic model.

A Data Flow chart has four basic graphical symbols:

------->: Arrow, indicating data flow;

0: circle or elliptic, indicating processing;

=
: Parallel bars, indicating data storage;

□: Box, indicating the source or end point of the data.

(1)
Data Flow. Data Stream is the path where data is transmitted in the system. Therefore, data streams are composed of fixed data. For example, a ticket consists of a passenger's name, age, unit, ID card number, date, destination, and other data items. Because a data stream is a flow of data, it must have a flow direction. In addition to the data stream between the data stream and the data storage, the data stream should be named by a noun or a noun phrase.

(2) Processing (also known as data processing ). Perform operations or transformations on data streams. Each processing should also have a name, usually a verb phrase, which briefly describes what processing is completed. In the layered data flow diagram, the processing should also be numbered.

(3) Data Storage (also called a file) refers to the temporary data stored. It can be a database file or any form of data organization.

(4) data source points or endpoints are entities (including personnel, organizations or other software systems) in the external environment of the software system, collectively referred to as external entities. Generally, only the top-level diagram of the data flow diagram is displayed.

Steps for drawing a data flow diagram:

(1) first draw the input and output of the system, that is, draw the top-layer data flow diagram. A top-level flow chart contains only one processing method to indicate the developed system, and then considers the input data and output data streams of the system. A top-level chart is used to indicate the scope of the developed system and its data exchange relationship with the surrounding environment.

 

(2) Draw a lower-layer data flow chart inside the system. Processing that is no longer decomposed is called basic processing. Generally, the layer number starts from 0 and adopts the principle of top-down and outward-internal. When a layer-0 data flow chart is drawn, the system that breaks down the top-layer data flow chart is a number of subsystems, and the data interface and Activity Relationship between each subsystem are determined.

 

2. Module

A module is a unit that can be combined, decomposed, and replaced. It is a basic unit that forms a system and is easy to process.

A module should have the following four elements:

(1) input and output: The Input Source and output destination are normally the same caller.

(2) function: refers to the work done by the module to convert input into output.

(3) Internal data: data that is only used by this module.

(4) program code: refers to the program used to implement module functions.

 

The first two elements are the external features of the module, which reflect the appearance of the module. The last two elements are the internal features of the module. Because each module has clear functions and is independent, it can be easily replaced and independently designed. When a module is added to or removed from the system, the function of this module is only added or reduced to the system, but has no or less impact on other modules. It is precisely this independence of the module that makes it easy to find errors, and effectively prevents the spread of errors in a module in the system, so that the system has good repair and modification and maintainability.