计算机二级必备干货——选择题基础知识（2）
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Share interest, spread happiness, increase knowledge, leave good! Dear, this is LearningYard's new school. Today xiaobian for you to bring computer level two essential dry goods - multiple choice basic knowledge (2).
软件工程基础
001．软件工程基本概念
软件是包括程序、数据及相关文档的完整集合。软件的特点：①软件是一种逻辑实体，具有抽象性。②软件的生产与硬件不同，没有明显的制作过程。③软件在运行、使用期间不存在磨损、老化问题。④软件的开发、运行对计算机系统具有依赖性，会给软件移植带来很多问题。⑤软件复杂性高，成本昂贵，现在软件成本已经大大超过硬件成本。⑥软件开发涉及诸多的社会因素。软件按功能可以分为应用软件、系统软件、支撑软件（或工具软件）。①应用软件是为解决特定领域的应用而开发的软件。②系统软件是计算机管理自身资源，提高计算机使用效率并服务于其他程序的软件。系统软件例如：操作系统、数据库管理系统、编译程序、汇编程序。③支撑软件是介于系统软件和应用软件之间，协助用户开发软件的工具性软件。
001. Basic concepts of Software engineering
Software is a complete collection of programs, data, and related documents.
Software features:
Software is a logical entity with abstractness.
② The production of software is different from that of hardware, and there is no obvious production process.
③ There is no wear and aging problem during the operation and use of the software.
(4) The development and operation of software depend on the computer system, which will bring many problems to the software transplantation.
(5) The complexity of software is high and the cost is expensive. Now the cost of software has greatly exceeded the cost of hardware.
⑥ Software development involves many social factors.
Software can be divided into Application software, system software and support software (or tool software) by function.
① Application software is the software developed to solve the application of a specific field.
② System software is the software that the computer manages its own resources, improves the efficiency of the computer and serves other programs. System software such as operating system, database management system, compiler, assembler.
③ Support software is a tool software between system software and application software to help users develop software.
002．软件危机和软件工程
软件危机主要表现在：①软件需求的增长得不到满足。用户对系统不满意的情况经常发生。②软件开发成本和进度无法控制。③软件质量难以保证。④软件不可维护或维护程度非常低。⑤软件测试成本不断提高。⑥软件开发生产率的提高赶不上硬件的发展和应用需求的增长。可以将软件危机归结为成本、质量、生产率等问题。软件工程包括3要素：方法、工具和过程。
002. Software crisis and software engineering
The software crisis is mainly manifested in:
① The growth of software demand is not being met. Users are often dissatisfied with the system
To happen.
② The cost and schedule of software development cannot be controlled.
③ It is difficult to guarantee the quality of software.
④ The software is not maintainable or the maintenance level is very low.
(5) The cost of software testing continues to increase.
⑥ The productivity of software development has not kept pace with the development of hardware and the growth of application Demand. Software crisis can be boiled down to cost, quality, productivity and other issues.
Software engineering consists of three elements: methods, tools and processes.
003．软件的生命周期
软件的生命周期从提出、实现、使用维护到停止使用退役的过程。软件生命周期分为三个阶段。①软件定义阶段：包括可行性研究制定计划、需求分析。②软件开发阶段：包括总体设计、详细设计、编码和测试。③软件维护阶段：在运行中不断维护，根据需求扩充和修改。
003. The software lifecycle
The software life cycle is a process from proposal, implementation, use and maintenance to decommissioning. The software life cycle is divided into three phases.
(1) Software definition stage: including feasibility study, plan making and demand analysis.
② Software development stage: including overall design, detailed design, coding and testing.
(3) Software maintenance stage: in the operation of continuous maintenance, according to the needs of expansion and modification.
004．结构化分析方法
1．需求分析及其方法需求分析阶段的工作主要有4个方面：①需求获取；②需求分析；③编写需求规格说明书；④需求评审。2．结构化分析方法常用工具①数据流图（DFD）；②数据字典（DD）；③判定表；④判定树。数据字典是结构化分析方法的核心。3．数据流图（DFD）建立数据流图的步骤：由外向里→自顶向下→逐层分解。
004. Structured analysis method
1. Requirements analysis and methods
The work of demand analysis stage mainly includes four aspects: (1) demand acquisition; ② Demand analysis; (3) Preparation of requirements specifications; ④ Demand review.
2. Common tools for structured analysis methods
① Data Flow graph (DFD); ② Data dictionary (DD); ③ Decision table; ④ Decision tree. Data dictionary is the core of structured analysis method.
3. Data Flow Diagram (DFD)
The steps of establishing data flow diagram: from outside-in to top-down to layer by layer decomposition.
005．软件需求规格说明书
1．软件需求规格说明书的作用①便于用户、开发人员进行理解和交流。②反映出用户问题的结构，可以作为软件开发工作的基础和依据。③作为确认测试和验收的依据。④为成本估算和编制计划进度提供基础。⑤软件不断改进的基础。2．软件需求规格说明书的内容软件需求规格说明应重点描述软件的目标、功能需求、性能需求、外部接口、属性及约束条件等。3．软件需求规格说明书的特点①正确性；②无歧义性；③完整性；④可验证性；⑤一致性；⑥可理解性；⑦可修改性；⑧可追踪性。
005. Software requirements specification
1. The role of software requirements specifications
① Easy for users and developers to understand and communicate.
② Reflect the structure of user problems, can be used as the foundation and basis of software development work.
③ As the basis for confirming the test and acceptance.
(4) To provide a basis for cost estimation and preparation of the schedule.
(5) The foundation of continuous improvement of software.
2. Contents of the software requirements specification
Software requirements specifications mainly describe software objectives, functional requirements, performance requirements, external interfaces, attributes, and constraints.
3. Characteristics of software requirements specifications
① Correctness; ② Unambiguous; ③ Integrity; ④ Verifiability; ⑤ Consistency; ⑥ Comprehensibility; ⑦ modifiability; Traceability.
006．结构化设计方法
1．技术角度软件设计包括软件结构设计、数据设计、接口设计、过程设计4个要点。2．工程管理角度软件设计分为概要设计（结构设计）和详细设计两部分。3．软件设计的基本原理软件设计应遵循软件工程的基本原理，主要包括抽象、逐步求精（模块化）、信息屏蔽（局部化）、模块独立性4个方面。①耦合性：用于衡量不同模块相互连接的紧密程度。②内聚性：用于衡量一个模块内部各个元素间彼此结合的紧密程度。好的软件设计应做到高内聚、低耦合。
006. Structured design method
1. Technical point of view
Software design includes software structure design, data design, interface design and process design.
2. Engineering management perspective
Software design is divided into two parts: outline design (structure design) and detailed design.
3. The fundamentals of software design
Software design should follow the basic principles of software engineering, mainly including abstraction, gradual refinement (modularization), information shielding (localization), module independence.
(1) Coupling: used to measure how closely different modules are connected to each other.
(2) Cohesion: used to measure the closeness of each element within a module.
Good software design should achieve high cohesion and low coupling.
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参考资料：百度百科、谷歌翻译。
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