【Chapter 1】什么是软件架构

Software systems are constructed to satisfy organizations’ business goals. The architecture is a bridge between those (often abstract) business goals and the inal (concrete) resulting system.
构建软件系统是为了满足组织的业务目标。而架构是这些（抽象）业务目标和最终的（具体）软件系统之间的桥梁。
These, then, are the topics for this book: the design, analysis,documentation, and implementation of architectures. We will also examine the inluences, principally in the form of business goals and quality attributes, which inform these activities.
架构活动包括：设计分析（评估）记录（文档化）实现，这些活动都受业务目标和质量属性的影响。
A structure is architectural if it supports reasoning about the system and the system’s properties. The reasoning should be about an attribute of the system that is important to some stakeholder. These include functionality achieved by the system, the availability of
the system in the face of faults, the dificulty of making speciic changes to the system, the responsiveness of the system to user requests, and many others.
如果一个结构支持推理系统和系统的属性，那这个结构就是一个架构。推理的系统属性应该是干系人关心（对于干系人重要）的，这些属性包括系统要实现的功能，系统在出现故障时的可用性，变更系统的困难程度，对于用户请求的响应性等等。
This means that architecture speciically omits certain information about elements that is not useful for reasoning about the system—in particular, it omits information that has no ramiications outside of a single element. Thus, an architecture is foremost an abstraction of a system that selects certain details and suppresses others. In all modern systems, elements interact with each other by means of interfaces that partition details about an element into public and private parts.
架构刻意忽略那些对推理整个系统没用元素的某些信息。因此，架构是一个系统最初的抽象，它选择某些细节同时抑制其他信息。现代系统中，元素之间通过接口进行交互，接口将公共部分和私有部分分离。
Architecture is concerned with the public side of this division; private details of elements—details having to do solely with internal implementation—are not architectural.
架构关心的是公共部分，私有部分的细节由各自的内部独立实现，这些私有的内部实现不属于架构。
System and Enterprise Architectures
软件架构系统架构企业架构的概念区别，参见P7（纸质版！）
The neurologist, the orthopedist, the hematologist, and the dermatologist all have different views of the structure of a human body. Ophthalmologists, cardiologists, and podiatrists concentrate on speciic subsystems. And the kinesiologist and psychiatrist are concerned with different aspects of the entire arrangement’s behavior. Although these views are pictured differently and have very different properties, all are inherently related, interconnected: together they describe the architecture of the human body
神经学医生、整形外科医生、血液学专家、皮肤科医生他们对人体的结构都有着各自的不同的视角。眼科医生、心脏病专家和足科医生专注于特定的子系统。运动学家和精神病学家关注的是整个行为的不同方面。虽然这些视角都不同，都具有不同的属性，但它们都是内在相关的，相互关联的:它们一起描述了人体的结构。
So it is with software. Modern systems are frequently too complex to grasp all at once. Instead, we restrict our attention at any one moment to one (or a small number) of the software system’s structures. To communicate meaningfully about an architecture, we must make clear which structure or structures we are discussing at the moment—which view we are taking of the architecture.
软件和人体结构的情况一样。现代系统因为太复杂了而难以一次把握。因此，我们采取在某一时刻只关注软件的一个结构或者部分结构的方法。
We will be using the related terms structure and view when discussing architecture representation.
■ A view is a representation of a coherent set of architectural elements, as written by and read by system stakeholders. It consists of a representation of a set of elements and the relations among them.
■ A structure is the set of elements itself, as they exist in software or hardware.
架构的表现有两个相关术语，一个是结构一个是视图。
■视图由一套连贯的架构元素组成，由系统的干系人读写。
架构的结构是软件架构的核心。架构的结构可以分为3大类：
Component-and-connector structures embody decisions as to how the system is to be structured as a set of elements that have runtime behavior (components) and interactions (connectors).
组件-连接器结构：提现了系统是如何通过一套有运行时的行为（组件）和交互（连接器）的元素组织起来的。
In these structures, the elements are runtime components (which are the principal units of computation and could be services, peers, clients, servers, ilters, or many other types of runtime elements) and connectors (which are the communication vehicles among components, such as call-return, process synchronization operators, pipes, or others).
运行时的组件是重要的运算单元，可以是：服务、对等体（端对端）、客户端、服务器、过滤器以及其他类型的运行时元素；
运行时的连接器是组件之间交流的载体工具，可以是调用-返回、进程同步操作、管道或者其他。
Component-and-connector views help us answer questions such as these:
■ What are the major executing components and how do they interact at runtime?
■ What are the major shared data stores? ■ Which parts of the system are replicated?
■ How does data progress through the system?
■ What parts of the system can run in parallel?
■ Can the system’s structure change as it executes and, if so, how?
组件-连接器可以解决如下问题：
●在运行时哪些是主要的执行组件以及它们之间是如何交互的？
●主要的共享数据存储有哪些？
●系统的哪部分是可复用的？
●在系统中数据如何处理？
●系统的哪些部分可以并行处理系统在执行时，它的结构会不会发生改变，如果改变，是如何改变的。
By extension, component-and-connector views are crucially important for asking questions about the system’s runtime properties such as performance, security, availability, and more.
并且，组件-连接器视图对系统运行时的属性，如：性能、安全、可用性等等提出问题是相当重要的。
Module structures embody decisions as to how the system is to be structured as a set of code or data units that have to be constructed or procured.
模块结构体现了系统是如何由一套必须的代码或数据单元来构造的。
In any module structure, the elements are modules of some kind (perhaps classes, or layers, or merely divisions of functionality, all of which are units of implementation).
模块可以由如下元素组成：类、层、部分功能，所有这些都是实现的单元。
Modules represent a static way of considering the system. Modules are assigned areas of functional responsibility; there is less emphasis in these structures on how the resulting software manifests itself at runtime。
模块结构很少关心软件在运行时的自身表现。模块展示了对系统的一种静态的思考。模块被分配了功能职责的一部分；
Module structures allow us to answer questions such as these:
■ What is the primary functional responsibility assigned to each module?
■ What other software elements is a module allowed to use?
■ What other software does it actually use and depend on?
■ What modules are related to other modules by generalization or specialization (i.e., inheritance) relationships?
模块结构可以帮助我们搞清楚如下问题：
■每个模块的主要功能职责
■模块允许使用哪些其他软件元素
■模块实际使用和依赖哪些其他软件
■模块间的关系是什么？泛化、继承？
In other words, examining a system’s module structures—that is, looking at its module views—is an excellent way to reason about a system’s modiiability。
通过查看系统的模块结构可推理出系统的可修改性。
Structures play such an important role in our perspective on software architecture because of the analytical and engineering power they hold. Each structure provides a perspective for reasoning about some of the relevant quality attributes. For example
因为结构拥有可分析和工程化的能力，所以结构在软件架构中扮演者重要的角色。每一种结构都为推理相关的质量属性提供了视角。例如：
■The module “uses” structure, which embodies what modules use what other modules, is strongly tied to the ease with which a system can be extended or contracted.
■ The concurrency structure, which embodies parallelism within the system, is strongly tied to the ease with which a system can be made free of deadlock and performance bottlenecks.
■ The deployment structure is strongly tied to the achievement of performance, availability, and security goals.
■模块结构大类中的“use”结构体现了哪些模块使用了其他模块，并且非常方便系统的扩展和压缩。
■并发结构体现了系统的并发性，与系统能够轻松避免死锁和性能瓶颈紧密相关。
■部署结构和系统的性能、可用性、和安全目标的实现紧密相连。
Allocation structures embody decisions as to how the system will relate to nonsoftware structures in its environment (such as CPUs, file systems, networks, development teams, etc.).
分配结构体现了系统在其环境中（如，CPU、文件系统、网络、开发团队等等）如何与非软件系统进行联系。
These structures show the relationship between the software elements and elements in one or more external environments in which the software is created and executed.
这些结构展示了系统元素和在创建和执行软件的一个或多个环境中的元素的关系。
Allocation views help us answer questions such as these:
■ What processor does each software element execute on?
■ In what directories or files is each element stored during development, testing, and system building?
■ What is the assignment of each software element to development teams?
分配视图可以帮助我们回答如下问题：
■软件元素在哪个处理器上执行？
■在开发、测试、系统构建的过程中元素存储在哪些目录或文件中？
■开发团队接收到的元素开发任务是什么？
And so forth. Each structure provides the architect with a different insight into the design (that is, each structure can be analyzed for its ability to deliver a quality attribute). But perhaps more important, each structure presents the architect with an engineering leverage point: By designing the structures appropriately, the desired quality attributes emerge.
每一种结构都为架构师提供了一种不同的视角来看待设计（也就是说，可以分析出每一种结构的能力/作用来交付一种质量属性）。
但是，可能更重要的是结构给架构师提供了一个工程杠杆支点：只要合理的设计结构就会得到想要的质量属性。

一些好的成熟的模块结构：
分解结构：
The units are modules that are related to each other by the is-a-submodule-of relation, showing how modules are decomposed into smaller modules recursively until the modules are small enough
to be easily understood.
这些模块是通过“是一种子模块”的关系来与其他模块产生关联，展示了这些模块是如何被递归的分解成更小的模块，以便可以很轻松的理解他们。类似分而治之的思想。
Modules often have products (such as interface specifications, code, test plans, etc.) associated with them.
这些模块通常和接口文档、代码、测试计划等联系在一起。

The decomposition structure determines, to a large degree, the system’s modifiability, by assuring that likely changes are localized. That
is, changes fall within the purview of at most a few (preferably small) modules.
因为分解结构可以保证变化是局部的，所以，可以在很大程度上决定系统的可修改性。也就是说，更改只能属于少数（并且是小的）模块内。

The units in this structure tend to have names that are organization-specific such as “segment” or “subsystem.”
这些分解结构也被称为“片段”或“子系统”。

“uses”结构：
In this important but overlooked structure, the units here are also modules, perhaps classes. The units are related by the uses relation,
a specialized form of dependency
这种结构虽然重要但是常被忽略，这些单元可能是类。他们通过“使用关系”来产生关联，一种特殊的依赖形式。

A unit of software uses another if the correctness of the first requires the presence of a correctly functioning
version (as opposed to a stub) of the second.
如果第一个软件单元的正确性需要第二个软件单元的正确运行版本(而不是存根)的存在，那么这个软件单元就会使用另一个软件单元。

The uses structure is used to engineer systems that can be extended to add functionality, or from which
useful functional subsets can be extracted.
uses结构用于设计可以扩展以添加功能的系统，或者可以从中提取有用的功能子集。

The ability to easily create asubset of a system allows for incremental development.
轻松创建系统子集的功能允许增量开发。

分层结构：

The modules in this structure are called layers. A layer is an abstract “virtual machine” that provides a cohesive set of services
through a managed interface.
分层是一种抽象的虚拟机，它通过一个托管理的接口来提供一套内聚的服务。

Layers are allowed to use other layers in a strictly managed fashion; in strictly layered systems, a layer is only allowed
to use the layer immediately below
分层在使用其他层的时候采用严格的管理方式；在严格的分层系统中，一个层只允许调用它直接的下层。

This structure is used to imbue a system with portability, the ability to change the underlying computing platform
这种结构用于为系统注入可移植性，即改变底层计算平台的能力。

类（泛化）结构：

The module units in this structure are called classes. The relation is inherits from or is an instance of. This view
supports reasoning about collections of similar behavior or capability (e.g., the classes that other classes inherit from) and parameterized differences.
类结构体现的关系是 ”继承“或”是谁的实例“。类结构视图支持推理相似的行为或能力（该类继承其他类）的集合以及参数化差异。

The class structure allows one to reason about reuse and the incremental addition of functionality.
类结构允许人们考虑重用和增加额外的功能。

If any documentation exists for a project that has followed an object-oriented analysis and design process, it is typically this structure
任何面向对象的分析和设计过程都是典型的类结构

数据模型结构：

The data model describes the static information structure in terms of data entities and their relationships
数据模型描述的是静态信息结构，静态信息结构是指数据实体以及实体之间的关系。

For example, in a banking system, entities will typically include Account, Customer, and Loan。
例如，在银行系统中，实体通常包括账号、客户和贷款。

Account has several attributes, such as account number, type (savings or checking), status, and current balance. A relationship may dictate that one
customer can have one or more accounts, and one account is associated to one or two customers.
账户有多种属性，例如账号、类型（储蓄或支票）、状态以及当前余额。关系可以是规定：一个客户可以有一个或多个账号，一个账户可以关联一个或多个客户。

一些好的成熟的组件-连接器结构：

Component-and-connector structures show a runtime view of the system. In these structures the modules described above have all been compiled into executable
forms.

组件-连接器结构展示了系统运行时的视图。在这些运行时的结构中，之前描述的“Modules”结构都被编译成了可执行的形式。

All component-and-connector structures are thus orthogonal to the module-based structures and deal with the dynamic aspects of a running system.
所有的组件-连接器结构都与基于“Module”的结构产生正交，并且处理运行时系统的动态方面。

The relation in all component-and-connector structures is attachment, showing how the components and the connectors are hooked together（The connectors themselves can be familiar constructs such as “invokes.”）
组件-连接器中的关系都是连接物，展示了组件和连接器如何连接在一起（连接器本身可以是熟悉的结构，如“调用”。）。

服务结构：

The units here are services that interoperate with each other by service coordination mechanisms such as SOAP (see Chapter 6).
组成服务结构的单元是通过服务协调机制(如SOAP)彼此互操作的服务(见第6章)

The service structure is an important structure to help engineer a system composed of components that may have been developed anonymously and
independently of each other

服务结构是一种重要的结构，它有助于设计出一个由各种相互独立并且相互匿名的组件组成的系统。

并发结构：

This component-and-connector structure allows the architect to determine opportunities for parallelism and the locations where resource contention may occur
组件和连接器结构允许架构师确定并行的机会和可能发生资源争用的位置。

The units are components and the connectors are their communication mechanisms.
组件和连接器是并发结构通信机制。

The components are arranged into logical threads; a logical thread is a sequence of computations that could be allocated to a separate physical thread later in the design process.
组件被安排进了逻辑线程；一个逻辑线程是一个在后续的设计过程中被分配给一个独立的物理线程的计算序列。

The concurrency structure is used early in the design process to identify the requirements to manage the issues associated with concurrent execution.
并发结构在设计过程的早期使用，以识别并管理与并发执行相关的问题的需求

一些好的成熟的分配结构

Allocation structures define how the elements from C&C or module structures map onto things that are not software: typically hardware, teams, and file systems
非配结构的定义是：如果将组件-连接器结构或者模块结构映射到非软件的事物上去：如、通常是硬件、团队及文件系统。

部署结构：
The deployment structure shows how software isassigned to hardware processing and communication elements
部署结构显示了如何将软件分配给硬件以对元素进行处理和通信。

The elements are software elements (usually a process from a C&C view), hardware entities (processors), and communication pathways.

这些元素是：软件元素(从组件-连接器视图来看，通常是一个进程)、硬件实体(处理器)和通信路径。

Relations are allocated-to, showing on which physical units the software elements reside,and migrates-to if the allocation is dynamic
针对分配关系，那就展示软件元素驻留在哪个物理单元上；如果是动态分配，那就展示软件元素迁移到哪个物理单元。

This structure can be used to reason about performance, data integrity, security, and availability. It is of particular interest in distributed and parallel systems
这个结构可以用来分析性能、数据完整性、安全性和可用性。它在分布式和并行系统中尤为重要。

实现结构：

This structure shows how software elements (usually modules) are mapped to the file structure(s) in the system’s development, integration, or configuration control environments
实现结构显示了软件元素(通常是模块)是如何映射到系统开发、集成或配置控制环境中的文件结构中的。

This is critical for the management of development activities and build processes. (In practice, a screenshot of your development environment tool, which manages
the implementation environment, often makes a very useful and sufficient diagram of your implementation view.)
这对于开发活动和构建过程的管理至关重要。(在实践中，管理实现环境的开发环境工具的截图，通常会形成非常有用和充分的实现视图图。)

工作分配结构：

This structure assigns responsibility for implementing and integrating the modules to the teams who will carry it out。
工作分配结构将实现和集成模块的责任分配给将负责实现的团队。

Having a work assignment structure be part of the architecture makes it clear that the decision about who does the work has architectural as well as
management implications。
将工作分配结构作为体系结构的一部分，可以清楚地表明由谁来完成工作的决策具有体系结构和管理方面的含义。

Also, on large multi-sourced distributed development projects, the work assignment structure is the means for calling out units of
functional commonality and assigning those to a single team, rather than having them implemented by everyone who needs them. This structure will
also determine the major communication pathways among the teams: regular teleconferences, wikis, email lists, and so forth.

同样，在大型多源分布式开发项目中，工作分配结构是调用功能公共单元并将其分配给单个团队的方法，而不是让每个需要它们的人实现它们。这个结构还将确定团队之间的主要通信路径:定期电话会议、wiki、电子邮件列表，等等。

翻译自《软件架构实践》

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