需求工程 | Rye Land

The process of finding out, analysing, documenting and checking the services and constraints of a software system is called requirements engineering (RE).

需求管理

大型软件系统的需求总是在变化的，一个系统一旦被正式使用，不可避免会产生新的需求。一般有三个基本阶段：

问题分析和变更描述

变更分析和成本计算

变更实现

There are three key activities in RE

需求引出和分析

Requirements elicitation and analysis: interact with stakeholders, discovering the user and system requirements.

需求发现

Requirements discovery：有时称“需求导出”，是一个对准备建立的系统和正在使用的系统进行信息收集，并从这些信息当中提取需求的过程。有以下常见的发现技巧：

采访

Interview

封闭式采访 （Closed Interviews）

信息持有者回答一组预定的问题（Stakeholders answers a predefined set of questions）

开放式采访 （Open Interviews）

没有一个预先准备好的程序，需求工程团队即兴提问（free form discussions with stakeholders）

场景

Scenarios: describe how the system can be use for some particular task

（探索）具体的使用场景，用于描述系统或软件在不同情境下的行为和交互。

描述用户在特定情境下使用软件的行为和交互。场景通常包括特定的输入和预期的输出，以及用户的行为和系统的反应。

例如，当用户点击”购买”按钮时，系统应该显示一个确认对话框，询问用户是否确定购买此商品，并提示用户输入付款信息。

深入实际

Ethnography, the scientific description of different races and cultures, is an observational technique that can be used to understand operational processes and help derive requirements for software to support these processes.

💡原译为“人种学”，是“人类学“的分支，是一种研究人类文化和社会行为的方法，可以应用于软件开发的过程中，了解用户的需求。

Immerse yourself in the working environment

Observe day-to-day work and taking notes

Discover implicit requirements of the system

The Importance of the Observation Activity

Actual work practices are far richer, more complex, and more dynamic than the models assumed

People often find it very difficulty to clearly articulate details of their work

People may understand their own work, but may not understand its relationship to other work in the organization

(2022 Final Exam) Ethnography is a technique used during the requirements elicitation and analysis stage of requirements engineering. State the importance of using the technique in requirements engineering. (Make three main points and use an example to support your answer).

Understanding users and environments. Ethnography can help development teams uncover implicit needs that users may not be able to articulate.

Improving product quality. By observing user behavior and needs, teams can gain a better understanding of how the product will make improvements to its functionality.

Promoting team collaboration. By working with users together, team members from different departments can gain a better understanding of each other's work to achieve common goals.

需求分类和组织

Requirements classification and organization: take the unstructured collection of requirements, groups related requirements

需要向不同类型的读者传达系统信息，因此不同层次的需求是有用的。

用户需求

User requirements

Usually written for non-technical people

Often written in natural langue with diagrams

High level, abstract statement of a service that a system should provide or a constraint on a system

系统需求

System requirements

Usually written for technical people

Detailed description of software system’s services and operational constraints

Define exactly what is to be implemented

It may be part of the contract between system investors and software developers

功能需求

Functional Requirements: focused on what system should should do.

E.g., How the system should react to particular inputs? How the system should behave in a particular situation?

非功能需求

Non-functional Requirements: specify characteristics of the system as a whole. E.g., reliability, performance, security, etc.

指不直接关系到系统向用户提供的具体服务的一类需求。它们与系统的总体特性相关，如可靠性、响应时间和储存空间占用等。

Functional Requirements	Non-Functional Requirements
Describe what the software must do	Describe how the software must perform
Focused on specific features and functions	Focused on overall quality and performance
Easier to define and measure	More difficult to define and measure

1️⃣

需求的分类

2️⃣

需求的度量

Non functional Requirements must be testable, So, 如何评判非功能需求的实现程度？

→ 转化为 Measurable Non-Functional Requirements

把质量需求，如性能、可靠性、安全性等非功能需求，转化为具体场景，在特定环境下对系统进行相应的刺激 (stimulus)，从而根据系统反应进行测试。

*Example: Quality Attribute Scenario for System Reliability*

3️⃣

需求产生的冲突

Issues with too Many Non-Functional Requirements

Many non-functional requirements conflict with others, e.g., speed/security, scalability/availability.

Realizing a non-functional requirement may require staffs to have specialized skills

Extra resources may be needed, for example, specially configured tested, more time required for testing, extra budget to spend on hiring external specialists, etc.