Requirements analysis refers to the process that developers should accurately understand users' requirements, conduct detailed investigation and analysis, and transform users' informal requirements into complete requirements definitions, and then into corresponding formal functional specifications (requirements specifications). Although requirement analysis is the beginning of software development process, it is very important to the whole software development process and the quality of software products.

Requirements analysis is the most basic task, that is, to accurately define the objectives of the new system and answer the question of what the system must do.

Structured analysis is a method to analyze the requirements of data streams. SA is also a decomposition, which describes the software model that meets the functional requirements.

Service agreement analysis steps:

Understand the workflow of the current system or obtain the physical model of the current system. The current system refers to the currently running system, which may be a software system running on a computer that needs improvement or a manual processing system.

Abstract the logical model of the current system. The physical model reflects the concrete realization of the system "how to do it", removes the non-essential factors in the physical model and abstracts the essential factors. Essential factors refer to the inherent system, which changes with different environments and different implementations.

Establish the logical model of the target system. Target system refers to a system with development. Analyze and compare the logical differences between the target system and the current system, and then decompose the "changed part" again. According to their own experience, analysts gradually determine the internal structure of the changed part by adopting the analysis strategy of top-down gradual refinement, thus establishing the logical model of the target system.

Make further supplements and optimizations. In order to describe the target system completely, we need to make some supplements: explain the man-machine interface of the target system; Explain the details that have not been considered in detail so far.

4. Overall design

The basic tasks of software overall design include: software architecture design, data structure and database design.

Structural design of (1) software system.

In order to realize the target system, the software structure is designed first, and the specific steps are as follows:

1) uses certain design methods to divide a complex system into modules according to functions.

2) Determine the function of each module.

3) Determine the calling relationship between modules.

4) Determine the interface between modules, that is, the information transmitted between modules.

5) Evaluate the quality of the module structure.

(2) Data structure and database design.

1) data structure design To design an effective data structure through gradual refinement will greatly simplify the design of software module processing.

2) Database design. Database design refers to the design of data storage files, mainly in concept, logic and physics.