blocks|key|50698|text|Wikipedia|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|50699|50700|在软件工程中，多层体系结构(通常称为n层体系结构)是一种客户端-服务器体系结构，其中的表示、应用程序处理和数据管理是逻辑上分离的过程。例如，使用中间件为用户和数据库之间的数据请求提供服务的应用程序采用多层体系结构。最广泛使用的“多层架构”指的是三层架构。|blockquote|50701|50702|50703|什么是“层”是有争议的，但在我看来，它至少需要跨越进程边界。否则它就被称为层。但是，它不需要在物理上不同的机器中。虽然我不推荐这样做，但您可以在同一机器上托管逻辑层和数据库。|50704|​|50705|📷|atomic|50706|50707|编辑：一种含义是表示层和逻辑层(有时称为业务逻辑层)需要“跨越网络”跨越机器边界，有时跨越不可靠、缓慢和/或不安全的网络。这与简单的桌面应用程序非常不同，在桌面应用程序中，数据与文件驻留在同一台计算机上，或者在Web应用程序中，您可以直接访问数据库。|style|BOLD|50708|对于n层编程，您需要将数据打包成某种称为“数据集”的可传输形式，并通过网络传输它们。.NET的DataSet类或Web+Services协议(如SOAP+)很少尝试通过网络传输对象。|50709|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Multitier_architecture|1|IMAGE|IMMUTABLE|imageUrl|https://upload.wikimedia.org/wikipedia/en/6/66/Overview_of_a_three-tier_application.png|imageAlt|2|http://msdn.microsoft.com/en-us/library/system.data.dataset.aspx|3|http://www.w3.org/TR/soap/^0|0|9|0|0|0|0|0|0|0|0|0|1|1|0|0|0|2|0|1B|7|2|20|4|3|0^^$0|@$1|2|3|4|5|6|7|1F|8|@]|9|@$A|1G|B|1H|1|1I]]|C|$]]|$1|D|3|-4|5|6|7|1J|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|1K|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1L|8|@]|9|@]|C|$]]|$1|I|3|-4|5|6|7|1M|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|1N|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|1O|8|@]|9|@]|C|$]]|$1|N|3|O|5|P|7|1P|8|@]|9|@$A|1Q|B|1R|1|1S]]|C|$]]|$1|Q|3|M|5|6|7|1T|8|@]|9|@]|C|$]]|$1|R|3|S|5|6|7|1U|8|@$A|1V|B|1W|T|U]]|9|@]|C|$]]|$1|V|3|W|5|6|7|1X|8|@]|9|@$A|1Y|B|1Z|1|20]|$A|21|B|22|1|23]]|C|$]]|$1|X|3|-4|5|6|7|24|8|@]|9|@]|C|$]]]|Y|$Z|$5|10|11|12|C|$13|14]]|15|$5|16|11|17|C|$18|19|1A|-4]]|1B|$5|10|11|12|C|$13|1C]]|1D|$5|10|11|12|C|$13|1E]]]]

<a href="http://en.wikipedia.org/wiki/Multitier_architecture" rel="noreferrer">Wikipedia</a>:

<blockquote>
 In software engineering, multi-tier
 architecture (often referred to as
 n-tier architecture) is a
 client-server architecture in which,
 the presentation, the application
 processing and the data management are
 logically separate processes. For
 example, an application that uses
 middleware to service data requests
 between a user and a database employs
 multi-tier architecture. The most
 widespread use of "multi-tier
 architecture" refers to three-tier
 architecture.
</blockquote>

It's debatable what counts as "tiers," but in my opinion it needs to at least cross the process boundary. Or else it's called layers. But, it does not need to be in physically different machines. Although I don't recommend it, you can host logical tier and database on the same box.

<img src="https://upload.wikimedia.org/wikipedia/en/6/66/Overview_of_a_three-tier_application.png" alt="alt text">

Edit: One implication is that presentation tier and the logic tier (sometimes called Business Logic Layer) needs to cross machine boundaries "across the wire" sometimes over unreliable, slow, and/or insecure network. This is very different from simple Desktop application where the data lives on the same machine as files or Web Application where you can hit the database directly.

For n-tier programming, you need to package up the data in some sort of transportable form called "dataset" and fly them over the wire. .NET's <a href="http://msdn.microsoft.com/en-us/library/system.data.dataset.aspx" rel="noreferrer">DataSet</a> class or Web Services protocol like <a href="http://www.w3.org/TR/soap/" rel="noreferrer">SOAP</a> are few of such attempts to fly objects over the wire.

blocks|key|50749|text|它基于表示层与核心业务逻辑和数据访问(Wikipedia)的分离方式。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|50750|50751|3-tier是表示层%2B组件层%2B数据访问层。|unordered-list-item|50752|N-tier是指在这些层之外添加附加层，通常是为了增加模块性、可配置性或与其他系统的互操作性。|50753|50754|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Front-end_and_back-end|1|http://en.wikipedia.org/wiki/Multitier_architecture^0|J|9|0|0|0|0|6|1|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|H|3|I|5|G|7|13|8|@]|9|@]|C|$]]|$1|J|3|-4|5|6|7|14|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]]]

It's based on how you separate the presentation layer from the core business logic and data access (<a href="http://en.wikipedia.org/wiki/Front-end_and_back-end" rel="nofollow noreferrer">Wikipedia</a>)

<ul>
<li><a href="http://en.wikipedia.org/wiki/Multitier_architecture" rel="nofollow noreferrer">3-tier</a> means Presentation layer + Component layer + Data access layer. </li>
<li>N-tier is when additional layers are added beyond these, usually for additional modularity, configurability, or interoperability with other systems.</li>
</ul>

blocks|key|888525|text|这是一个时髦的词，指的是普通的网络架构，例如，Javascript+-+ASP.Net+-+Middleware+-+Database+layer。这些东西中的每一个都是“层”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|888526|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It's a buzzword that refers to things like the normal Web architecture with e.g., Javascript - ASP.Net - Middleware - Database layer. Each of these things is a "tier".

blocks|key|3272036|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3272037|+N层数据应用程序是分成多个层的数据应用程序。也称为“分布式应用程序”和“多层应用程序”，n层应用程序将处理分离到分布在客户端和服务器之间的离散层。当您开发访问数据的应用程序时，您应该在组成应用程序的各个层之间有一个清晰的分离。|blockquote|3272038|3272039|典型的n层应用程序包括表示层、中间层和数据层。在n层应用程序中分隔各个层的最简单方法是为要包含在应用程序中的每个层创建离散的项目。例如，表示层可能是Windows窗体应用程序，而数据访问逻辑可能是位于中间层的类库。此外，表示层可以通过服务等服务与中间层中的数据访问逻辑进行通信。将应用程序组件分成不同的层可以提高应用程序的可维护性和可伸缩性。它通过更容易地采用可应用于单个层的新技术来实现这一点，而无需重新设计整个解决方案。此外，n层应用程序通常在中间层存储敏感信息，中间层保持与表示层的隔离。|3272040|3272041|取自微软website。|offset|length|3272042|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/bb384398.aspx^0|0|0|0|0|0|4|7|0|0^^$0|@$1|2|3|-4|4|5|6|T|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|U|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|V|7|@]|8|@]|9|$]]|$1|E|3|F|4|5|6|W|7|@]|8|@]|9|$]]|$1|G|3|-4|4|5|6|X|7|@]|8|@]|9|$]]|$1|H|3|I|4|5|6|Y|7|@]|8|@$J|Z|K|10|1|11]]|9|$]]|$1|L|3|-4|4|5|6|12|7|@]|8|@]|9|$]]]|M|$N|$4|O|P|Q|9|$R|S]]]]

<blockquote>
 N-tier data applications are data applications that are separated into
 multiple tiers. Also called "distributed applications" and "multitier
 applications," n-tier applications separate processing into discrete
 tiers that are distributed between the client and the server. When you
 develop applications that access data, you should have a clear
 separation between the various tiers that make up the application.
 
 A typical n-tier application includes a presentation tier, a middle
 tier, and a data tier. The easiest way to separate the various tiers
 in an n-tier application is to create discrete projects for each tier
 that you want to include in your application. For example, the
 presentation tier might be a Windows Forms application, whereas the
 data access logic might be a class library located in the middle tier.
 Additionally, the presentation layer might communicate with the data
 access logic in the middle tier through a service such as a service.
 Separating application components into separate tiers increases the
 maintainability and scalability of the application. It does this by
 enabling easier adoption of new technologies that can be applied to a
 single tier without the requirement to redesign the whole solution. In
 addition, n-tier applications typically store sensitive information in
 the middle-tier, which maintains isolation from the presentation tier.
</blockquote>

Taken from Microsoft <a href="https://msdn.microsoft.com/en-us/library/bb384398.aspx" rel="nofollow">website</a>.

blocks|key|4117646|text|如果我理解了这个问题，那么在我看来，提问者实际上是在问“好吧，3层是很好理解的，但围绕4层或泛化的N层架构的含义，似乎存在炒作、困惑和不确定的混合。那么……什么是被广泛理解和同意的N层的定义？”|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4117647|这实际上是一个相当深刻的问题，为了解释为什么，我需要更深入一点。听我说。|4117648|经典的3层架构:数据库、“业务逻辑”和表示，是阐明如何遵守关注点分离原则的好方法。也就是说，如果我想要改变“业务”想要为客户提供服务的方式，我不应该查看整个系统来找出如何做到这一点，特别是决策业务问题不应该随意分散在代码中。|4117649|现在，这个模型已经很好地服务了几十年，它是经典的“客户端-服务器”模型。快进到云产品，web浏览器是广泛的物理分布的用户集的用户界面，一个典型的结果是必须添加内容分发服务，这些服务不是经典的3层架构的一部分(并且需要自己管理)。|4117650|当涉及到服务、微服务、数据和计算如何分布等等时，这个概念就是泛化的。某物是否为“层”在很大程度上取决于该层是否为该层后面(或下面)的服务提供了接口和部署模型。因此，内容分发网络将是一个层，但身份验证服务不是。|4117651|现在，考虑到这个概念，去阅读N层架构示例的其他描述，您就会开始理解这个问题。其他观点包括基于供应商的方法(例如NGINX)、内容感知负载均衡器、数据隔离和安全服务(例如IBM+Datapower)，所有这些都可能会也可能不会为给定的体系结构、部署和用例增加价值。|4117652|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|P|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Q|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|S|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|M|$]]

If I understand the question, then it seems to me that the questioner is really asking "OK, so 3-tier is well understood, but it seems that there's a mix of hype, confusion, and uncertainty around what 4-tier, or to generalize, N-tier architectures mean. So...what's a definition of N-tier that is widely understood and agreed upon?"

It's actually a fairly deep question, and to explain why, I need to go a little deeper. Bear with me.

The classic 3-tier architecture: database, "business logic" and presentation, is a good way to clarify how to honor the principle of separation of concerns. Which is to say, if I want to change how "the business" wants to service customers, I should not have to look through the entire system to figure out how to do this, and in particular, decisions business issues shouldn't be scattered willy-nilly through the code. 

Now, this model served well for decades, and it is the classic 'client-server' model. Fast forward to cloud offerings, where web browsers are the user interface for a broad and physically distributed set of users, and one typically ends up having to add content distribution services, which aren't a part of the classic 3-tier architecture (and which need to be managed in their own right).

The concept generalizes when it comes to services, micro-services, how data and computation are distributed and so on. Whether or not something is a 'tier' largely comes down to whether or not the tier provides an interface and deployment model to services that are behind (or beneath) the tier. So a content distribution network would be a tier, but an authentication service would not be. 

Now, go and read other descriptions of examples of N-tier architectures with this concept in mind, and you will begin to understand the issue. Other perspectives include vendor-based approaches (e.g. NGINX), content-aware load balancers, data isolation and security services (e.g. IBM Datapower), all of which may or may not add value to a given architecture, deployment, and use cases.

blocks|key|4117173|text|据我所知，N-Tier使用独立的物理机将业务逻辑、客户端访问和数据彼此分离。理论上，它们中的一个可以独立于其他的进行更新。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4117174|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It's my understanding that N-Tier separates business logic, client access and data from each other using separate physical machines. The theory is that one of them can be updated independently of the others.

blocks|key|4117486|text|N层数据应用程序是分成多个层的数据应用程序。也称为“分布式应用程序”和“多层应用程序”，n层应用程序将处理分离到分布在客户端和服务器之间的离散层。当您开发访问数据的应用程序时，您应该在组成应用程序的各个层之间有一个清晰的分离。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4117487|在http://msdn.microsoft.com/en-us/library/bb384398.aspx中依此类推|offset|length|4117488|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/bb384398.aspx^0|0|1|1H|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

N-tier data applications are data applications that are separated into multiple tiers. Also called "distributed applications" and "multitier applications," n-tier applications separate processing into discrete tiers that are distributed between the client and the server. When you develop applications that access data, you should have a clear separation between the various tiers that make up the application.

And so on in <a href="http://msdn.microsoft.com/en-us/library/bb384398.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/bb384398.aspx</a>

blocks|key|4117733|text|当构建通常的MCV+(3层体系结构)时，可以决定实现具有双层接口的MCV，这样实际上可以在不修改一行代码的情况下替换特定的层。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4117734|我们经常看到这种的好处，例如，在你想要使用多个数据库的情况下(在这种情况下，你在控制层和数据层之间有一个双重接口)。|offset|length|style|BOLD|4117735|当你把它放在视图层(演示)上时，你就可以(坚持住！！)用另一台机器替换用户界面，从而自动化实际输入(！)-因此，您可以运行繁琐的可用性测试数千次，而任何用户都不必一遍又一遍地点击相同的东西。|4117736|有些人将具有1个或2个双接口的3层体系结构描述为4层或5层体系结构，隐含地暗示了双接口。|4117737|其他情况包括(但不限于)这样一个事实，即在半复制或完全复制数据库的情况下，系统实际上能够将其中一个数据库视为“主数据库”，因此您将拥有一个由主数据库组成的层和另一个由从数据库组成的层。|4117738|移动示例|4117739|因此，多层-或N-层-确实有一些解释，而我肯定会坚持由夹在中间的瘦接口磁盘组成的3层%2B额外层，以实现层交换，并且在测试方面(特别是在移动设备上使用)，您现在可以在真实软件上运行用户测试，通过模拟用户点击的方式，控制逻辑无法区分真实用户点击。这在模拟真实用户测试的中几乎是至关重要的，因为您可以记录来自用户的所有输入，然后在进行回归测试时重用相同的输入。|4117740|entityMap^0|0|0|8|0|0|F|6|O|2|R|2|0|0|0|4|0|0|A|2N|6|3N|19|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@$D|V|E|W|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|Y|8|@$D|Z|E|10|F|G]|$D|11|E|12|F|G]|$D|13|E|14|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|15|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|16|8|@$D|17|E|18|F|G]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|19|8|@$D|1A|E|1B|F|G]|$D|1C|E|1D|F|G]|$D|1E|E|1F|F|G]]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|S|$]]

When constructing the usual MCV (a 3-tier architecture) one can decide to implement the MCV with double-deck interfaces, such that one can in fact replace a particular tier without having to modify even one line of code. 

We often see the benefits of this, for instance in scenarios where you want to be able to use more than one database (in which case you have a double-interface between the control and data-layers). 

When you put it on the View-layer (presentation), then you can (hold on!!) replace the USER interface with another machine, thereby automate REAL input (!!!) - and you can thereby run tedious usability tests thousands of times without any user having to tap and re-tap and re-re-tap the same things over and over again.

Some describe such 3-tier architecture with 1 or 2 double-interfaces as 4-tier or 5-tier architecture, implicitly implying the double-interfaces.

Other cases include (but are not limited to) the fact that you - in case of semi-or-fully replicated database-systems would practically be able to consider one of the databases as the "master", and thereby you would have a tier comprising of the master and another comprising of the slave database. 

Mobile example

Therefore, multi-tier - or N-tier - indeed has a few interpretations, whereas I would surely stick to the 3-tier + extra tiers comprising of thin interface-disks wedged in between to enable said tier-swaps, and in terms of testing (particularly used on mobile devices), you can now run user tests on the real software, by simulating a users tapping in ways which the control logic cannot distinguish from a real user tapping. This is almost paramount in simulating real user tests, in that you can record all inputs from the users OTA, and then re-use the same input when doing regression tests.

blocks|key|893541|text|当我们谈论层时，我们通常谈论物理进程(具有不同的内存空间)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|893542|因此，如果应用程序的层部署在不同的进程中，这些不同的进程将是不同的层。|893543|893544|例如，在一个3层的应用程序中，业务层与大型机(独立的进程)对话，并与报告服务(独立的进程)对话，那么该应用程序将是5层。|blockquote|893545|893546|893547|因此，通用名称是n-tier。|893548|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|Q|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|R|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|S|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|T|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|U|8|@]|9|@]|A|$]]]|M|$]]

When we talk of Tiers, we generally talk of Physical Processes (having different memory space).

Thus, in case, Layers of an application are deployed in different processes, those different processes will be different tiers. 

<blockquote>
 E.g, In a 3-tier application, business tier talks to Mainframes (separate process) and talks to Reporting Service (separate process), then that application would be 5 tier.
</blockquote>

Hence, the generic name is n-tier.

blocks|key|51165|text|来自https://docs.microsoft.com/en-us/azure/architecture/guide/architecture-styles/n-tier|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|51166|N层体系结构主要将应用轮胎划分为逻辑轮胎和物理层，并将它们划分为子部分。|style|BOLD|51167|📷|atomic|51168|​|51169|层是分离职责和管理依赖关系的一种方式。每一层都有特定的职责。较高层可以使用较低层中的服务，但反之亦然。|51170|各层在物理上是分开的，运行在不同的机器上。一个层可以直接调用另一个层，或者使用异步消息传递(消息队列)。尽管每一层都可以托管在自己的层中，但这并不是必需的。可以在同一层上托管多个层。以物理方式分隔各层可提高可扩展性和恢复能力，但也会增加额外网络通信的延迟。|51171|传统的三层应用程序有一个表示层、一个中间层和一个数据库层。中间层是可选的。更复杂的应用程序可以有三个以上的层。上图显示了一个具有两个中间层的应用程序，封装了不同的功能区域。|51172|N层应用程序可以具有封闭层体系结构或开放层体系结构：|51173|In+a+closed+layer+architecture,+a+layer+can+only+call+the+next+layer+immediately+down.
In+an+open+layer+architecture,+a+layer+can+call+any+of+the+layers+below+it.|code-block|syntax|javascript|51174|封闭层架构限制了层之间的依赖关系。但是，如果一层只是将请求传递到下一层，则可能会产生不必要的网络流量。|51175|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/azure/architecture/guide/architecture-styles/n-tier|1|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/5d75260c0462897b6b95763b54062e8c.png|imageAlt^0|2|2C|0|0|9|4|G|4|L|3|0|0|1|1|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1F|8|@]|9|@$A|1G|B|1H|1|1I]]|C|$]]|$1|D|3|E|5|6|7|1J|8|@$A|1K|B|1L|F|G]|$A|1M|B|1N|F|G]|$A|1O|B|1P|F|G]]|9|@]|C|$]]|$1|H|3|I|5|J|7|1Q|8|@]|9|@$A|1R|B|1S|1|1T]]|C|$]]|$1|K|3|L|5|6|7|1U|8|@]|9|@]|C|$]]|$1|M|3|N|5|6|7|1V|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1W|8|@]|9|@]|C|$]]|$1|Q|3|R|5|6|7|1X|8|@]|9|@]|C|$]]|$1|S|3|T|5|6|7|1Y|8|@]|9|@]|C|$]]|$1|U|3|V|5|W|7|1Z|8|@]|9|@]|C|$X|Y]]|$1|Z|3|10|5|6|7|20|8|@]|9|@]|C|$]]|$1|11|3|-4|5|6|7|21|8|@]|9|@]|C|$]]]|12|$13|$5|14|15|16|C|$17|18]]|19|$5|1A|15|1B|C|$1C|1D|1E|-4]]]]

from <a href="https://docs.microsoft.com/en-us/azure/architecture/guide/architecture-styles/n-tier" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/architecture/guide/architecture-styles/n-tier</a>

An N-tier architecture divides an application tires into logical tiresand physical tiers mainly and their are divide to sub parts.
<a href="https://i.stack.imgur.com/rAtGm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rAtGm.png" alt="enter image description here"></a>

Layers are a way to separate responsibilities and manage dependencies. Each layer has a specific responsibility. A higher layer can use services in a lower layer, but not the other way around.

Tiers are physically separated, running on separate machines. A tier can call to another tier directly, or use asynchronous messaging (message queue). Although each layer might be hosted in its own tier, that's not required. Several layers might be hosted on the same tier. Physically separating the tiers improves scalability and resiliency, but also adds latency from the additional network communication.

A traditional three-tier application has a presentation tier, a middle tier, and a database tier. The middle tier is optional. More complex applications can have more than three tiers. The diagram above shows an application with two middle tiers, encapsulating different areas of functionality.

An N-tier application can have a closed layer architecture or an open layer architecture:

<pre><code>In a closed layer architecture, a layer can only call the next layer immediately down.
In an open layer architecture, a layer can call any of the layers below it.
</code></pre>

A closed layer architecture limits the dependencies between layers. However, it might create unnecessary network traffic, if one layer simply passes requests along to the next layer.

blocks|key|4117937|text|N层应用程序是包含三个以上组件的应用程序。这些组件是什么？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4117938|用于异步行为的|4117939|Cache|unordered-list-item|4117940|Message队列|4117941|加载|4117942|4117943|Message服务器，以便在处理大量data|4117944|Components时涉及的大量data|4117945|Components进行搜索运行异构技术，通常称为web服务等。|4117946|4117947|4117948|所有的社交应用如Instagram，Facebook，大型行业服务如Uber，Airbnb，在线大型多人游戏如Pokemon+Go，具有奇特功能的应用程序都是n层应用程序。|4117949|entityMap^0|0|0|0|0|1|1|1|1|1|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|F|7|11|8|@]|9|@]|A|$]]|$1|K|3|E|5|F|7|12|8|@]|9|@]|A|$]]|$1|L|3|M|5|F|7|13|8|@]|9|@]|A|$]]|$1|N|3|O|5|F|7|14|8|@]|9|@]|A|$]]|$1|P|3|Q|5|F|7|15|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|18|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|W|$]]

An N-tier application is an application which has more than three components involved.
What are those components?

<ul>
<li>Cache</li>
<li>Message queues for asynchronous behaviour</li>
<li>Load balancers</li>
<li>Search servers for searching through massive amounts of data</li>
<li>Components involved in processing massive amounts of data</li>
<li>Components running heterogeneous tech commonly known as web services
etc.</li>
</ul>

All the social applications like Instagram, Facebook, large scale industry services like Uber, Airbnb, online massive multiplayer games like Pokemon Go, applications with fancy features are n-tier applications.

blocks|key|4117893|text|马丁·福勒清楚地展示了：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4117894|分层是软件设计人员用来分解复杂软件系统的最常见的技术之一。你可以在机器架构中看到这一点，在机器架构中，层通过操作系统调用从编程语言下降到设备驱动程序和CPU指令集，以及芯片内部的逻辑门。网络将FTP分层在TCP之上，TCP位于IP之上，IP位于以太网之上。|4117895|当从层的角度考虑系统时，您可以想象软件中的主要子系统以某种形式的层饼形式排列，其中每一层都位于较低的层上。在该方案中，较高层使用由较低层定义的各种服务，但较低层不知道较高层。此外，每一层通常对上面的层隐藏其下层，因此第四层使用第三层的服务，第三层使用第二层的服务，但是第四层不知道第二层。(并不是所有的分层体系结构都像这样不透明，但大多数都是--或者更确切地说，大多数是不透明的)。|4117896|将系统分解为多个层有许多重要的好处。|4117897|·您可以将单个层理解为一个连贯的整体，而无需对其他层了解太多。您可以了解如何在TCP之上构建FTP服务，而无需了解以太网如何工作的细节。|4117898|·您可以使用相同基本服务的替代实现来替换层。FTP服务可以在以太网、PPP或有线电视公司使用的任何设备上运行而无需更改。|4117899|·最小化各层之间的依赖关系。如果有线电视公司改变了它的物理传输系统，只要他们能使用IP，我们就不必改变我们的FTP服务。|4117900|·层是标准化的好地方。TCP和IP是标准，因为它们定义了各自层的工作方式。|4117901|·一旦您构建了一个层，您就可以将其用于许多更高级别的服务。因此，FTP、telnet、SSH和HTTP都使用TCP/IP。否则，所有这些较高级别的协议都必须编写自己的较低级别的协议。摘自凯尔·杰弗里·帕萨雷利图书馆|4117902|分层是一项重要的技术，但也有缺点。|4117903|·层很好地封装了一些东西，但不是所有的东西。因此，您有时会得到级联更改。分层企业应用程序中的典型示例是添加一个字段，该字段需要显示在UI上，必须在数据库中，因此必须添加到中间的每一层。|4117904|·额外的层可能会损害性能。在每一层，事物通常都需要从一种表示转换到另一种表示。但是，底层函数的封装通常会给您带来超过补偿的效率收益。可以对控制事务的层进行优化，然后让一切变得更快。但是，分层体系结构最困难的部分是决定拥有哪些层以及每一层的职责是什么。|4117905|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|11|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|12|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|14|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|15|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|16|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|17|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|18|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|19|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|1A|8|@]|9|@]|A|$]]|$1|X|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Y|$]]

Martin Fowler demonstrating clearly:

Layering is one of the most common techniques that software designers use to
break apart a complicated software system. You see it in machine architectures,
where layers descend from a programming language with operating system calls
into device drivers and CPU instruction sets, and into logic gates inside chips.
Networking has FTP layered on top of TCP, which is on top of IP, which is on
top of ethernet.

When thinking of a system in terms of layers, you imagine the principal subsystems
in the software arranged in some form of layer cake, where each layer
rests on a lower layer. In this scheme the higher layer uses various services
defined by the lower layer, but the lower layer is unaware of the higher layer.
Furthermore, each layer usually hides its lower layers from the layers above, so
layer 4 uses the services of layer 3, which uses the services of layer 2, but layer 4
is unaware of layer 2. (Not all layering architectures are opaque like this, but
most are—or rather most are mostly opaque.)

Breaking down a system into layers has a number of important benefits.

• You can understand a single layer as a coherent whole without knowing
much about the other layers. You can understand how to build an FTP service
on top of TCP without knowing the details of how ethernet works.

• You can substitute layers with alternative implementations of the same
basic services. An FTP service can run without change over ethernet, PPP,
or whatever a cable company uses.

• You minimize dependencies between layers. If the cable company changes
its physical transmission system, providing they make IP work, we don’t
have to alter our FTP service.

• Layers make good places for standardization. TCP and IP are standards
because they define how their layers should operate.

• Once you have a layer built, you can use it for many higher-level services.
Thus, TCP/IP is used by FTP, telnet, SSH, and HTTP. Otherwise, all of these
higher-level protocols would have to write their own lower-level protocols.
From the Library of Kyle Geoffrey Passarelli

Layering is an important technique, but there are downsides.

• Layers encapsulate some, but not all, things well. As a result you sometimes
get cascading changes. The classic example of this in a layered enterprise
application is adding a field that needs to display on the UI, must be
in the database, and thus must be added to every layer in between.

• Extra layers can harm performance. At every layer things typically need to
be transformed from one representation to another. However, the encapsulation
of an underlying function often gives you efficiency gains that more
than compensate. A layer that controls transactions can be optimized and
will then make everything faster.
But the hardest part of a layered architecture is deciding what layers to have
and what the responsibility of each layer should be.

I've seen quite a few developer job postings recently that include a sentence that reads more or less like this: "Must have experience with N-Tier architecture", or "Must be able to develop N-Tier apps".

This leads me to ask, what is N-Tier architecture? How does one gain experience with it?

What is N-Tier architecture?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我最近看到了相当多的开发人员招聘广告，其中有一句话读起来或多或少是这样的：“必须有N-Tier架构的经验”，或者“必须能够开发N-Tier应用程序”。这让我不禁要问，什么是N-Tier架构？如何获得使用它的经验？

问什么是N-Tier架构？
EN

回答 12

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