专业英语

高频考点词汇

软件工程模型 waterfall, incremental, iterative, spiral, agile, prototyping

项目管理 stakeholder, milestone, deliverable, baseline, tailoring, schedule

数据库核心 schema, instance, attribute, normalization, transaction, concurrency

云计算 virtualization, IaaS, PaaS, SaaS, connected, infrastructure

通用技术 architecture, framework, implementation, specification, requirement

逻辑关系词/描述词 rarely, invaluable, efficiently, abstract, de facto (事实上的)

影响阅读补充：

duplicated重复的，impractical不切实际的， explicitly明确地，implicitly含蓄地，sumptions假设，implementer实施者，briefings简报

软件工程类

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常考场景：题目描述"分阶段交付"→选 incremental；"快速响应变化"→选 agile；"风险驱动"→选 spiral

项目管理类

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常考场景："对标准过程进行调整"→选 tailoring；"经批准的版本"→选 baseline

数据库类

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常考场景：ACID 中的 A（Atomicity）原子性、C（Consistency）一致性等也常考

通用技术类

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常考搭配：requirement specification（需求规格说明）、software architecture（软件体系结构）

考试解题速记口诀

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真题

1

For nearly ten years， the Unified Modeling Language (UML) has been the industry standard for visualizing， specifying， constructing， and documenting the （ 1 ）of a software-intensive system.As the （ 2 ）standard modeling language， the UML facilitates communication and reduces confusion among project （ 3 ）.The recent standardization of UML 2.0 has further extended the language’s scope and viability. Its inherent expressiveness allows users to（ 4 ）everything from enterprise information systems and distributed Web-based applications to real-time embedded systems.The UML is not limited to modeling software. In fact， it is expressive enough to model （ 5 ）systems， such as workflow in the legal system， the structure and behavior of a patient healthcare system， software engineering in aircraft combat systems， and the design of hardware.To understand the UML， you need to form a conceptual model of the language， and this requires learning three major elements: the UML’s basic building blocks， the rules that dictate how those building blocks may be put together， and some common mechanisms that apply throughout the UML.

①artifacts：Artifacts 在软件工程中不是"人工制品"的日常意思，而是特指：软件开发过程中产生的一切有形产出物，涵盖"代码+模型+文档"全部产物。

这里就与前面四个动词（visualizing, specifying, constructing, documenting）完美对应。

近十年来，统一建模语言（UML）一直是可视化、规范说明、构建和记录软件密集型系统的开发制品的行业标准。

②de facto：这是标准领域的拉丁语借词：（事实上的 / 实际上的）。

作为事实上的标准建模语言

③stakeholders：干系人 / 利益相关者，任何影响项目决策、活动或结果，或受项目影响、自认为受项目影响的个人、群体或组织。

UML 的核心价值是可视化沟通和减少歧义，UML 是画给所有干系人看的，不是只给程序员看的所以必须是 stakeholders。

UML 促进了沟通并减少了项目干系人之间的误解。

④model

其固有的表达能力允许用户对从企业信息系统、分布式 Web 应用到实时嵌入式系统的所有事物进行建模。

⑤non-software：这里注意上句话才提到不局限于对软件建模

UML 并不局限于对软件进行建模。事实上，它的表达能力足以对非软件系统进行建模

2

Observe that for the programmer, as for the chef, the urgency of the patron （顾客）may govern the scheduled completion of the task, but it cannot govern the actual completion. An omelette（煎鸡蛋）, promised in two minutes, may appear to be progressing nicely. But when it has not set in two minutes, the customer has two choices—waits or eats it raw. Software customers have had（ 6 ）choices.

Now I do not think software（ 7 ）have less inherent courage and firmness than chefs, nor than other engineering managers. But false（ 8 ）to match the patron’s desired date is much more common in our discipline than elsewhere in engineering. It is very（ 9 ）to make a vigorous, plausible, and job risking defense of an estimate that is derived by no quantitative method, supported by little data, and certified chiefly by the hunches of the managers.

Clearly two solutions are needed.We need to develop and publicize productivity figures, bug-incidence figures, estimating rules, and so on. The whole profession can only profit from（ 10 ）such data.Until estimating is on a sounder basis, individual managers will need to stiffen their backbones and defend their estimates with the assurance that their poor hunches are better than wish derived estimates.

⑥the same

请注意，对于程序员而言，正如对于厨师一样，顾客的紧迫程度可以决定任务计划完成的时间，但无法决定实际完成的时间。一个承诺两分钟内做好的煎蛋，看起来可能进展顺利。但当两分钟过去煎蛋还没凝固时，顾客只有两种选择——要么等着，要么生吃。软件顾客也面临同样的选择。

⑦ managers：注意原意是把 software managers（软件经理）和其他工程经理放在同一层级做对比。

现在我不认为软件经理比厨师、比其他工程经理的勇气和坚定性差

⑧scheduling：这里的scheduling和后面说的date是对应的

但是，为了迎合顾客期望的日期而进行虚假排期，在我们的学科中比其他工程领域要常见得多。

⑨difficult

要为一个估算进行有力、看似合理且足以赌上职业生涯的辩护是非常困难的——尤其是当这个估算：并非来自任何定量方法，几乎没有数据支撑，且主要凭经理们的直觉拍板而定的时候。

⑩sharing

显然需要两种解决方案。我们需要开发并公布生产率数据、缺陷发生率数据、估算规则等等。整个业界都能从共享这类数据中获益。

3

Ravi, like many project（ 1 ）,had studied the waterfall model of software development as the primary software life-cycle（ 2 ）．He was all set to use it for an upcoming project, his first assignment． However, Ravi found that the waterfall model could not be used because the customer wanted the software delivered in stages, something that implied that the system had to be delivered and built in （ 3 ） and not as（ 4 ）.

The situation in many other projects is not very different． The real world rarely presents a problem in which a standard process, or the process used in a previous project, is the best choice． To be the most suitable, an existing process must be（ 5 ）to the new problem．

A development process, even after tailoring, generally cannot handle change requests．To accommodate change requests without losing control of the project, you must supplement the development process with a requirement change management process．

看到 project ___，优先考虑 manager(s)；看到 life-cycle ___，优先考虑 process / model

①managers：选择生命周期模型是项目经理的决策职责

②software life-cycle process ： "软件生命周期过程"，是软件工程的固定搭配

拉维像许多项目经理一样，曾将软件开发的瀑布模型作为主要软件生命周期过程来学习。

③parts，主要是既和后面的a whole对应，也是分阶段交付固定的搭配

④a whole，选项中和delivered in stages符合not as相反的、表达整体的只有a whole

然而，拉维发现瀑布模型无法使用，因为客户希望软件分阶段交付——这意味着系统必须以部分方式交付和构建，而不是作为一个整体。

⑤tailored：为...量身定制/裁剪，而且Tailoring 在软件工程和质量管理体系中是一个正式术语，前面suitable已经出现过了

为了成为最合适的选择，现有的过程必须针对新问题进行裁剪适配。

4

At a basic level, cloud computing is simply a means of delivering IT resources as （ 6 ）.Almost all IT resources can be delivered as a cloud service: applications, compute power, storage capacity， networking, programming tools, even communication services and collaboration （ 7 ）。

Cloud computing began as large-scale Internet service providers such as Google, Amazon, and others built out their infrastructure. An architecture emerged: massively scaled, （ 8 ） distributed system resources, abstracted as virtual IT services and managed as continuously configured, pooled resources. In this architecture, the data is mostly resident on （ 9 ）“somewhere on the Internet”and the application runs on both the "cloud servers”and the user’s browser.

Both clouds and grids are built to scale horizontally very efficiently. Both are built to withstand failures of （ 10 ） elements or nodes. Both are charged on a per-use basis. But while grids typically process batch jobs， with a defined start and end point, cloud services can be continuous. What’s more, clouds expand the types of resources available —— file storage, databases, and Web services —— and extend the applicability to Web and enterprise applications.

⑥services

⑦tools，其他的选项一系列例举compute power/storage capacity已经出现了，而且协助工具collaboration tools和Programming tools是相对应的。

从基本层面看，云计算只是将 IT 资源作为服务交付的一种方式。几乎所有 IT 资源都可以作为云服务交付：应用、计算能力、存储容量、网络、编程工具，甚至通信服务和协作工具。

⑧horizontally，云计算架构的特征是能够通过增加更多的机器（节点）来扩展系统，这种扩展方式在计算机科学中被称为 “水平扩展”。而且水平拓展在后文中还重复出现了。

一种架构出现了：大规模扩展的、水平分布的系统资源，被抽象为虚拟 IT 服务，并作为连续配置的资源池进行管理。

⑨servers

在这类架构中，数据主要驻留在“互联网某处”的服务器上，而应用程序则同时在“云服务器”和用户的浏览器上运行。

⑩individual

云和网格（网格计算）都是为了非常高效地进行水平扩展而构建的。两者也都被设计为能够承受单个元素或节点的故障。

5

So it is today. Schedule disaster,functional misfits,and system bugs all arise because the left hand doesn’t know what the right hand is doing. As work（ 1 ）,the several teams slowly change the functions, sizes, and speeds of their own programs, and they explicitly or implicitly（ 2 ）their assumptions about the inputs available and the uses to be made of the outputs.

For example, the implementer of a program-overlaying function may run into problems and reduce speed relying on statistics that show how（ 3 ）this function will arise in application programs. Meanwhile, back at the ranch, his neighbor may be designing a major part of the supervisor so that it critically depends upon the speed of this function. This change in speed itself becomes a major specification change,and it needs to be proclaimed abroad and weighed from a system point of view.

How , then , shall teams（ 4 ）with one another ? In as many ways as possible：

Informally . Good telephone services and a clear definition of intergroup dependencies will encourage the hundreds of calls upon which common interpretation of written documents depends.

Meetings . Regular project meetings, with one team after another giving technical briefings ,are（ 5 ）. Hundreds of minor misunderstandings get smoked out this way.

Workbook . A formal project workbook must be started at the beginning.

①proceeds：As work proceeds 是描述项目随时间推进的标准表达。

②change：因果对应，因为团队修改了程序（前半句），所以他们关于输入和输出的假设也就随之改变了（后半句）。

随着工作的推进，各个团队慢慢地改变着他们自己程序的功能、规模和速度，并且他们显式或隐式地改变了关于可用输入和输出用途的假设。

③rarely：要注意到前面说了reduce speed，然后这里就是为什么要reduce，而且另外三个选项基本都是频繁的意思，排除法也能选出来

例如，程序覆盖功能的实现者可能会遇到问题并降低速度，因为他们依据的统计数据显示该功能在应用程序中极少出现。

④communicate：要注意到在原文中主要讲的是信息传递的事情，相互沟通较为正式的用法就是Communicate with。

那么，团队之间应该如何沟通呢？要尽可能用多种方式：非正式地。良好的电话服务和对组间依赖关系的清晰定义，将促成数百次通话——而这些通话正是对书面文档形成共同理解的基础。

⑤invaluable：极有价值的、无价的。其他选项意思完全相反。

定期项目会议，各团队依次进行技术简报，是极有价值的。数百个微小误解通过这种方式被消除。

6

Why Have Formal Documents?

First, writing the decisions down is essential. Only when one writes do the gaps appear and the （ 6 ） protrude(突出). The act of writing turns out to require hundreds of mini-decisions, and it is the existence of these that distinguishes clear, exact policies from fuzzy ones.

Second, the documents will communicate the decisions to others. The manager will be continually amazed that policies he took for common knowledge are totally unknown by some member of his team. Since his fundamental job is to keep everybody going in the （ 7 ） direction, his chief daily task will be communication, not decision-making, and his documents will be immensely （ 8 ） this load.

Finally, a manager's documents give him a data base and checklist. By reviewing them （ 9 ） he sees where he is, and he sees what changes of emphasis or shifts in direction are needed.

The task of the manager is to develop a plan and then to realize it. But only the written plan is precise and communicable. Such a plan consists of documents on what, when, how much, where, and who. This small set of critical documents （ 10 ） much of the manager's work. If their comprehensive and critical nature is recognized in the beginning, the manager can approach them as friendly tools rather than annoying busywork. He will set his direction much more crisply and quickly by doing so.

⑥inconsistencies：不一致、矛盾，前面的gaps缺口/空白显现，后面就会出现不一致、矛盾。而且另外三个选项基本都有稳定的含义，排除法可以得出。

为什么需要正式文档？首先，将决策写下来至关重要。只有当一个人写下来时，缺口才会显现，矛盾之处才会突显。

⑦same

⑧lighten：lighten the load就是减轻负担的意思。这里主要是固定的一个搭配。

由于他的根本工作是让所有人朝同一方向前进，他的主要日常任务将是沟通，而非决策，而他的文档将极大地减轻这一负担。

⑨periodically：周期性回顾文档，另外三个意思完全相反。

最后，管理者的文档为他提供了一个数据库和检查清单。通过定期审阅这些文档，他能看清自己所处的位置，也能发现需要在重点上做出哪些调整、在方向上做出哪些转变。

⑩encapsulates：压缩;概括;简述

这样的计划包含关于“做什么、何时做、做多少、在哪里做以及由谁做”的文档。这少量关键文档概括了管理者的绝大部分工作。

7

In the fields of physical security and information security, access control is the selective restriction of access to a place or other resource. The act of accessing may mean consuming, entering, or using. Permission to access a resource is called authorization（授权）.

An access control mechanism（ 1 ）between a user （or a process executing on behalf of a user） and system resources, such as applications, operating systems, firewalls; routers, files,and databases. The system must first authenticate（验证）a user seeking access. Typically the authentication function determines whether the user is （ 2 ） to access the system at all.

Then the access control function determines if the specific requested access by this user is permitted. A security administrator maintains an authorization database that specifies what type of access to which resources is allowed for this user. The access control function consults this database to determine whether to（ 3 ） access. An auditing function monitors and keeps a record of user accesses to system resources.

In practice, a number of（ 4 ）may cooperatively share the access control function. All Operating systems have at least a rudimentary（基本的）. And in many cases a quite robust, access control component. Add-on security packages can add to the （ 5 ）access control capabilities of the OS. Particular applications .or utilities, such as a database management system, also incorporate access control functions. External devices, such as firewalls, can also provide access control services .

①mediates：协调、调解、仲裁。在信息安全领域，访问控制机制的核心功能是主动判断和控制访问权限。这里主要是一个专业英语，访问控制机制常被称为"access mediator"（访问调解器）。

访问控制机制在用户（或代表用户执行的进程）与系统资源（如应用程序、操作系统、防火墙、路由器、文件和数据库）之间进行协调/调解。

② permitted

系统必须首先验证试图访问的用户身份。通常，认证功能决定用户是否被允许访问系统。

③grant：数据库对应的赋予权限就是grant

访问控制功能查询该数据库，以确定是否授予访问权限。

④components：在操作系统中，访问控制功能由系统内部组件（如安全模块、内核组件、服务进程等）实现。这里注意cooperatively share指多个系统组件协同实现了访问控制的功能function。

在实践中，多个组件可能协同共享访问控制功能。

⑤native：native最准确描述操作系统内建的、原生的访问控制能力，安全包在此基础上进行增强。这里可以类比成selinux，访问控制是需要配置的本地系统功能。

附加的安全包可以增强操作系统的原生访问控制能力。

8

The beauty of software is in its function, in its internal structure, and in the way in which it is created by a team. To a user, a program with just the right features presented through an intuitive and （ 6 ） interface is beautiful.To a software designer, an internal structure that is partitioned in a simple and intuitive manner, and that minimizes internal coupling is beautiful.To developers and managers, a motivated team of developers making significant progress every week, and producing defect-free code, is beautiful. There is beauty on all these levels.

Our world needs software -- lots of software. Fifty years ago software was something that ran in a few big and expensive machines. Thirty years ago it was something that ran in most companies and industrial settings. Now there is software running in our cell phones, watches, appliances, automobiles, toys, and tools. And need for new and better software never （ 7 ）. As our civilization grows and expands，as developing nations build their infrastructures, as developed nations strive to achieve ever greater efficiencies，the need for more and more software （ 8 ）to increase. It would be a great shame if, in all that software，there was no beauty.

We know that software can be ugly. We know that it can be hard to use, unreliable, and carelessly structured. We know that there are software systems whose tangled and careless internal structures make them expensive and difficult to change. We know that there are software systems that present their features through an awkward and cumbersome interface.We know that there are software systems that crash and misbehave. These are （ 9 ） systems. Unfortunately, as a profession, software developers tend to create more ugly systems than beautiful ones.

There is a secret at the best software developers know. Beauty is cheaper than ugliness. Beauty is faster than ugliness. A beautiful software system can be built and maintained in less time, and for less money, than an ugly one. Novice software developers don't understand is. They think that they have to do everything fast and quick.They think that beauty is （ 10 ）. No! By doing things fast and quick, they make messes that make the software stiff and hard to understand. Beautiful systems are flexible and easy to understand. Building them and maintaining them is a joy. It is ugliness that is impractical.Ugliness will slow you down and make your software expensive and brittle. Beautiful systems cost the least to build and maintain, and are delivered soonest.

⑥simple：这里指交互界面简约

对用户而言，一个功能恰到好处、界面直观简洁的程序是优美的。

⑦stop

如今，我们的手机、手表、家电、汽车、玩具和工具中都有软件在运行，而且对新软件和更好软件的需求永无止境。

⑧continues：首先根据原文，需求不是忽然出现而是增长。并且通过排除法判断，其他选项都有相同的出现含义，或者意思完全相反。

随着人类文明的发展与扩张，发展中国家建设基础设施，发达国家追求更高效率，对软件的需求持续增长。如果在所有这些软件中缺乏美感，将是一种巨大的遗憾。

⑨Ugly：这里要注意后文说更多的丑陋系统

我们深知，存在一些会崩溃、运行不稳定的软件系统，这些便是丑陋的系统。遗憾的是，软件开发者作为一个职业群体，往往创造出更多丑陋的系统，而非美观的系统。

⑩time-wasting

新手软件开发者往往不理解这一点：他们以为必须快速完成所有工作，认为追求美感是在浪费时间。不！正是这种快速完成的做法，让他们制造出混乱，使软件变得僵硬且难以理解。

9

A transaction is an action, or a series of actions, carried out by a single user or（ 1 ）, that accesses or changes the contents of the database.

A transaction should possess the four basic or so-called ACID properties:

Atomicity. The “all or nothing” property. A transaction is an（ 2 ） unit that is either performed in its entirety or is not performed at all.

Consistency . A transaction must transform the database from one consistent state to another consistent state.

Isolation.Transactions execute independently of one another. In other words, the partial effects of（ 3 ）transactions should not be visible to other transactions.

Durability.The effects of a successfully completed (committed)transaction are permanently recorded in the database and must not be lost because of a subsequent failure.

The four properties above, only（ 4 ）property is the responsibility of the concurrency control subsystem to ensure. It is the responsibility of both the（ 5 ）and the application developers to ensure consistency. To guarantee the Atomicity and Durability properties after a failure, a log file is needed.

①application program：数据库事务的执行主体通常包括用户直接操作和用户通过应用程式间接操作。

事务是由单个用户或应用程式执行的操作，或一系列操作，这些操作访问或修改数据库的内容。

②indivisible：这里涉及到数据库的ACID事务概念

原子性。即“全有或全无”特性。事务是一个不可分割的单元，要么全部执行，要么完全不执行。

③incomplete：这里涉及到数据库的ACID事务概念

隔离性。事务之间相互独立执行。即，未完成事务的中间状态对其他事务不可见。

④consistency：这里要注意到后文马上又提到了一致性

⑤DBMS（数据库管理系统）：提供机制来维护数据一致性

上述四个特性中，只有一致性特性是由并发控制子系统负责确保的。确保一致性是DBMS和应用开发者的共同责任。为了在故障后保证原子性和持久性，需要一个日志文件。

10

The entity-relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called （ 6 ）, and of relationships among these objects. An entity is a “thing” or “object” in the real world that is distinguishable from other objects. Entities are described in a database by a set of （ 7 ） . A relationship is an association among several entities. The set of all entities of the same type and the set of all relationships of the same type are termed an entity set and relationship set, respectively. The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram, which is built up from the following components: （ 8 ） represent entity set, （ 9 ） represent attributes, etc. In addition to entities and relations, the E-R model represents certain（ 10 ） to which the contents of a database must conform. The entity-relationship model is widely used in database design.

⑥entities：实体，主要是根据一前一后，前面刚说entity-relationship，后面就提到XXX and relationships。

实体-关系（E-R）数据模型基于对现实世界的认知，认为现实世界由一组基本对象（称为实体）以及这些对象之间的关系构成。

⑦attributes：属性，实体由一组属性来描述是数据库设计的概念知识。其他的选项都是一些具体的现实层面的实例。

实体在数据库中通过一组属性来描述。关系是多个实体之间的关联。

⑧rectangles：矩形

⑨ellipses：椭圆

Rectangles（矩形）和 ellipses（椭圆）是 E-R 图的标准符号：矩形表示实体集，椭圆表示属性。这是数据库理论中的固定图形规范，是软考必背的基础知识。

数据库的整体逻辑结构（模式）可以通过 E-R 图以图形方式表达，该图由以下组件构建：矩形代表实体集，椭圆代表属性等。

⑩ constraints：约束条件，在数据库理论中，E-R 模型（实体-关系模型） 由三大核心要素构成：Entities（实体）/Relationships（关系）/Constraints（约束）

除了实体和关系之外，E-R 模型还表示某些约束条件，数据库内容必须符合这些约束。

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Cloud computing is a phrase used to describe a variety of computing concepts that involve a large number of computers（ 1 ）through a real-time communication network such as the Internet. In science, cloud computing is a（ 2 ）for distributed computing over a network, and means the（ 3 ）to run a program or application on many connected computers at the same time.

The architecture of a cloud is developed at three layers: infrastructure, platform, and application, The infrastructure layer is built with virtualized computer, storage, and network resources. The platform layer is for general-purpose and repeated usage of the collection of software resources. The application layer is formed with a collection of all needed software modules for SaaS applications. The infrastructure layer serves as the（ 4 ）for building the platform layer of the cloud. In turn, the platform layer is a foundation for implementing the（ 5 ）layer for SaaS applications.

①Connected:这里主要是注意后面提到了通过实时通信如互联网进行......，在云计算语境中，大量计算机通过互联网进行连接，形成资源池。

云计算是一个用来描述多种计算概念的短语，这些概念涉及大量计算机通过实时通信网络（如互联网）进行连接的方式。

②synonym 同义词

③ability

在科学领域，云计算是网络分布式计算的同义词，指的是同时在多台联网计算机上运行程序或应用的能力。

④foundation:看到前文 infrastructure就很容易联想到基础，而且后文又出现了foundation。

⑤application 这里是云计算三层架构的标准模型和SaaS 的定义。看到saas就要想到向用户提供可直接使用的应用程序。

表格

基础设施层作为构建云平台层的基础。反过来，平台层又是实现 SaaS 应用程序应用层的基础。

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A database system is a collection of interrelated data and a set of programs that allow users to access and modify these data. A major purpose of a database system is to provide users with an（ 6 ）view of the data. That is, the system hides certain details of how the data are stored and maintained. For the system to be usable, it must retrieve data（ 7 ）. The need for efficiency has led designers to use complex data（ 8 ）to represent data in the database. Since many database-system users are not computer trained, developers hide the complexity from users through several levels of abstraction, to simplify users' interactions with the system. Physical level is the lowest level of abstraction that describes（ 9 ）the data are actually stored. Logical level is the next-higher level of abstraction that describes（ 10 ）data are stored in the database, and what relationships exist among those data. View level is the highest level of abstraction that describes only part of the entire database.

⑥abstract：数据库系统的一个主要目的是为用户提供数据的抽象视图。屏蔽底层复杂性，只呈现用户关心的逻辑结构。

数据库系统是相互关联的数据集合，以及一组允许用户访问和修改这些数据的程序。数据库系统的一个主要目的是为用户提供数据的抽象视图。

⑦efficiency：后文马上又提到了 The need for efficiency ...

也就是说，系统隐藏了数据存储和维护的某些细节。为了让系统可用，它必须高效地检索数据。

⑧structures

对效率的需求促使设计者们使用复杂的数据结构来表示数据库中的数据。

⑨how

物理层是最低层次的抽象，它描述了数据是如何实际存储的。

⑩what

逻辑层次是更高一级的抽象，描述了数据库中存储的数据内容及其之间的关联关系。

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When we talk about a database, we must differentiate between the database （ 1 ）,which is the logical design of the database, and the database （ 2 ）, which is a snapshot of the data in the database at a given instant in time. The concept of a relation corresponds to the programming-language notion of a variable, while the concept of a relation schema corresponds to the programming-language notion of type definition. In general, a relation schema consists of a list of（ 3 ）and their corresponding domains. The concept of a relation instance corresponds to the programming-language notion of a value of a （ 4 ） . The value of a given variable may change with time; similarly the contents of a relation instance may change with time as the relation is updated. In contrast, the （ 5 ） оf a relation does not generally change.

①schema 模式/架构，是数据库的逻辑结构和组织方式

②instance 实例，是数据库当前的状态，后文明显有instant

当我们谈论数据库时，必须区分数据库模式（schema），即数据库的逻辑设计，以及数据库实例（instance），即在某一特定时间点数据库中数据的快照。

③Attributes 属性，关系模式（relation schema）由属性（attributes）列表及其对应域（domains）组成，这是关系数据库的形式化标准定义。

一般来说，关系模式由一组属性及其对应的域组成。

④variable 变量，这里主要是和value对应。关系实例（relation instance）可以随时间改变（增删改数据）

⑤schema 与 instance 形成 In contrast 对比，schema（结构）一般不变化，instance（数据）经常变化

关系实例的概念对应于编程语言中变量的值的概念。一个给定变量的值可能随时间改变；类似地，关系实例的内容也可能随关系的更新而随时间改变。相反，关系的模式（schema）通常不会改变。