table of Contents
What are the requirements analysis process?
In the front, we carried out the software plan of the project, completed the feasibility study report, and knew what to do. In the next step, we need to further understand how the project should be done and answer the questions about what must be done.
The status of needs analysis
The last stage of the software system definition stage, accurately answering the question of what the system must do
What is the sign of the end?
Form requirements specifications
What are the requirements analysis process?
1. Answer what the system must do and describe in depth the functions and performance of the software. Perform more detailed studies on the basis of the feasibility study report
2. Determine the constraints of the software design and the details of the interface between the software and other system elements
3. Define other validity requirements of the software
Principles of Software Requirements Specification
Separate the function from the display, that is, describe "what to do" rather than "how to achieve"
It is necessary to be able to decompose and continuously refine the problem in a hierarchical manner (decompose an abstract problem in a hierarchical manner, and decompose it into sub-problems with different functions)
Decomposition method: horizontal decomposition, vertical decomposition
Data flow diagram
What is a data flow diagram?
It is a tool to describe the process of data processing. It represents the flow of information within the system and represents the logic processing function of the system
What are the characteristics?
Abstraction, generality, hierarchy
Data flow-oriented analysis method
Structured analysis methods . Use data flow graph DFD and data dictionary DD to describe
The core is to decompose and simplify the problem, separate physical and logical representations, and abstract the data and logic of the system
What are the advantages and disadvantages?
1. The overall concept is strong, and each layer clearly emphasizes "what to do", "what is needed", and "what to give"
2. It can reflect the flow and processing of data
3. Due to top-down analysis, it is easy to find logical errors in various parts of the system early and easy to modify
4. Easy to compare with computer processing
5. It's not intuitive, it usually needs to be summarized, abstracted, and corrected based on the analysis of the operation process.
6. Without the help of a computer system, manual drawing is too troublesome and heavy workload
The main graphic elements of the data flow diagram
Hierarchical data flow diagram (generally divided into 3 layers)
Example description
Example: Computer Teaching Material Sales System
Principles of checking and modifying data flow diagrams
All graphic symbols on the data flow diagram are limited to the aforementioned four basic graphic elements
The main diagram of the data flow diagram must include the basic elements of the interim period, none of which are indispensable
Each process has at least one input data stream and one output data stream
In the data flow diagram, the processing boxes need to be numbered by layer. The number indicates the level of the processing and the personal relationship between the upper and lower levels
It is stipulated that any data flow sub-graph must correspond to a processing of its upper layer, and the input data flow and output data flow of the two must be consistent
Tool for writing processing logic description
Structured English
Decision table
Decision tree
to sum up
Software plan and demand analysis are interdependent, software plan provides a basis for demand analysis, and demand analysis is disassembled and analyzed on the basis of software plan
At the end of the software plan, a feasibility study report needs to be generated, and requirements analysis form a requirement specification