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Specific types of clients include web browsers,email clients, andonline chat clients.

Specific types of servers includeweb servers,ftp servers,application servers, database

servers,name servers,mail servers,file servers,print servers, and terminal servers. Most webservices are also types of servers.

Contents

[hide]

1 Comparison to peer-to-peer architecture

2 Advantages

3 Disadvantages

4 See also

5 References

[edit]Comparison to peer-to-peer architecture

This section requiresexpansion.

In peer-to-peerarchitectures, each host or instance of the program can simultaneously act as

both a client and a server, and each has equivalent responsibilities and status.

Both clientserver and peer-to-peer architectures are in wide usage today. Details may be found

inComparison of Centralized (Client-Server) and Decentralized (Peer-to-Peer) Networking.

[edit]Advantages

In most cases, a clientserver architecture enables the roles and responsibilities of a

computing system to be distributed among several independent computers that are known to

each other only through a network. This creates an additional advantage to this architecture:

greater ease of maintenance. For example, it is possible to replace, repair, upgrade, or even

relocate a server while its clients remain both unaware and unaffected by that change.

All data is stored on the servers, which generally have far greater security controls than

most clients.[citation needed] Servers can better control access and resources, to guarantee that

only those clients with the appropriate permissions may access and change data.

Since data storageis centralized, updates to that data are far easier to administer in

comparison to aP2P paradigm. In the latter, data updates may need to be distributed and

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applied to each peer in the network, which is time-consuming as there can be thousands or

even millions of peers.

Many mature clientserver technologies are already available which were designed to

ensure security, friendliness of the user interface, and ease of use.[citation needed]

It functions with multiple different clients of different capabilities.

[edit]Disadvantages

As the number of simultaneous client requests to a given server increases, the server

can become overloaded. Contrast that to a P2P network, where its aggregated bandwidth

actually increases as nodes are added, since the P2P network's overall bandwidth can be

roughly computed as the sum of the bandwidths of every node in that network.

The clientserver paradigm lacks the robustness of a good P2P network.[citation needed] Under

clientserver, should a critical server fail, clients requests cannot be fulfilled. In P2P

networks, resources are usually distributed among many nodes. Even if one or more nodes

depart and abandon a downloading file, for example, the remaining nodes should still have

the data needed to complete the download.

[edit]See also

Hybrid client

Inter-server Mainframe computer

Mobile software

Name server

Observer pattern

Push technology

Pull technology

Servent

Standalone server Thin client

Multitier architecture

Client (computing)

Server (computing)

For other uses, see Three-tier system (disambiguation).

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This article does not cite anyreferences or sources.Please helpimprove this articleby adding citations to reliable sources. Unsourced material

may bechallengedandremoved.(January 2008)

In software engineering, multi-tier architecture (often referred to as n-tier architecture) is

aclientserver 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 is the three-tier architecture.

N-tier application architecture provides a model for developers to create a flexible and reusable

application. By breaking up an application into tiers, developers only have to modify or add a

specific layer, rather than have to rewrite the entire application over. There should be a

presentation tier, a business or data access tier, and a data tier.

The concepts of layer and tier are often used interchangeably. However, one fairly common point

of view is that there is indeed a difference, and that a layer is a logical structuring mechanism for

the elements that make up the software solution, while a tier is a physical structuring mechanism

for the system infrastructure.[1]

Contents

[hide]

1 Three-tier architecture

o 1.1 Comparison with the MVC architecture

o 1.2 Web development usage

o 1.3 Other considerations

o 1.4 Traceability

o 1.5 Comments

2 See also

3 External links

4 References

[edit]Three-tier architecture

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Visual overview of a Three-tiered application

Three-tier[2] is a clientserver architecture in which the user interface,functional process

logic ("business rules"),computer data storage anddata accessare developed and maintained as

independent modules, most often on separate platforms. It was developed by John J. Donovan in

Open Environment Corporation (OEC), a tools company he founded inCambridge,

Massachusetts.

The three-tier model is a software architecture and asoftware design pattern.

Apart from the usual advantages of modularsoftware with well-defined interfaces, the three-tier

architecture is intended to allow any of the three tiers to be upgraded or replaced independently

as requirements ortechnologychange. For example, a change ofoperating system in

thepresentation tierwould only affect the user interface code.

Typically, the user interface runs on a desktop PC orworkstation and uses a standard graphical

user interface, functional process logic may consist of one or more separate modules running on

a workstation orapplication server, and anRDBMS on a database serverormainframecontains

the computer data storage logic. The middle tier may be multi-tiered itself (in which case the

overall architecture is called an "n-tier architecture").

Three-tier architecture has the following three tiers:

Presentation tier

This is the topmost level of the application. The presentation tier displays information

related to such services as browsing merchandise, purchasing, and shopping cart

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contents. It communicates with other tiers by outputting results to the browser/client tier

and all other tiers in the network.

Application tier (business logic, logic tier, data access tier, or middle tier)

The logic tier is pulled out from the presentation tier and, as its own layer, it controls an

applications functionality by performing detailed processing.

Data tier

This tier consists of database servers. Here information is stored and retrieved. This tier

keeps data neutral and independent from application servers or business logic. Giving

data its own tier also improves scalability and performance.

[edit]Comparison with the MVC architecture

At first glance, the three tiers may seem similar to themodel-view-

controller(MVC) concept; however, topologically they are different. A

fundamental rule in a three tier architecture is the client tier never communicatesdirectly with the data tier; in a three-tier model all communication must pass

through the middle tier. Conceptually the three-tier architecture is linear.

However, the MVC architecture is triangular: the view sends updates to the

controller, the controller updates the model, and the view gets updated directly

from the model.

From a historical perspective the three-tier architecture concept emerged in the

1990s from observations of distributed systems (e.g., web applications) where

the client, middleware and data tiers ran on physically separate platforms.

Whereas MVC comes from the previous decade (by work at Xerox PARC in the

late 1970s and early 1980s) and is based on observations of applications that ran

on a single graphical workstation; MVC was applied to distributed applications

later in its history (see Model 2).

[edit]Web development usage

In the web development field, three-tier is often used to refer to websites,

commonlyelectronic commercewebsites, which are built using three tiers:

1. A front-end web serverserving static content, and potentially

some cached dynamic content. In web based application, Front End is

the content rendered by the browser. The content may be static or

generated dynamically.

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2. A middle dynamic content processing and generation

level application server, for example Java

EE,ASP.NET,PHP,ColdFusion platform.

3. A back-enddatabase, comprising both data sets and

the database management system orRDBMS software that manages

and provides access to the data.

[edit]Other considerations

Data transfer between tiers is part of the architecture. Protocols involved may

include one or more ofSNMP,CORBA,Java RMI,.NET Remoting,Windows

Communication Foundation,sockets,UDP,web services or other standard or

proprietary protocols. Often middleware is used to connect the separate tiers.

Separate tiers often (but not necessarily) run on separate physical servers, and

each tier may itself run on acluster.

[edit]Traceability

The end-to-end traceability of data flows through n-tier systems is a challenging

task which becomes more important when systems increase in complexity.

The Application Response Measurement defines concepts and APIs for

measuring performance and correlating transactions between tiers.

[edit]Comments

This article refers to tiers and layers as equivalent concepts. Generally, the term

tiers is used to describe physical distribution of components of a system on

separate servers, computers, or networks (processing nodes). A three-tier

architecture then will have three processing nodes. Layers refer to a logical

grouping of components which may or may not be physically located on one

processing node.

[edit]See also

Clientserver model Database-centric architecture

Front-end and back-end

Hierarchical internetworking model

Open Services Architecture

Rich Internet application

http://en.wikipedia.org/wiki/Application_serverhttp://en.wikipedia.org/wiki/Java_EEhttp://en.wikipedia.org/wiki/Java_EEhttp://en.wikipedia.org/wiki/ASP.NEThttp://en.wikipedia.org/wiki/ASP.NEThttp://en.wikipedia.org/wiki/ASP.NEThttp://en.wikipedia.org/wiki/PHPhttp://en.wikipedia.org/wiki/PHPhttp://en.wikipedia.org/wiki/ColdFusionhttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Database_management_systemhttp://en.wikipedia.org/wiki/Relational_database_management_systemhttp://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=4http://en.wikipedia.org/wiki/Simple_Network_Management_Protocolhttp://en.wikipedia.org/wiki/Simple_Network_Management_Protocolhttp://en.wikipedia.org/wiki/Simple_Network_Management_Protocolhttp://en.wikipedia.org/wiki/CORBAhttp://en.wikipedia.org/wiki/CORBAhttp://en.wikipedia.org/wiki/Java_RMIhttp://en.wikipedia.org/wiki/Java_RMIhttp://en.wikipedia.org/wiki/.NET_Remotinghttp://en.wikipedia.org/wiki/.NET_Remotinghttp://en.wikipedia.org/wiki/Windows_Communication_Foundationhttp://en.wikipedia.org/wiki/Windows_Communication_Foundationhttp://en.wikipedia.org/wiki/Windows_Communication_Foundationhttp://en.wikipedia.org/wiki/Internet_sockethttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Web_servicehttp://en.wikipedia.org/wiki/Middlewarehttp://en.wikipedia.org/wiki/Cluster_(computing)http://en.wikipedia.org/wiki/Cluster_(computing)http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=5http://en.wikipedia.org/wiki/Application_Response_Measurementhttp://en.wikipedia.org/wiki/APIhttp://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=7http://en.wikipedia.org/wiki/Client%E2%80%93server_modelhttp://en.wikipedia.org/wiki/Database-centric_architecturehttp://en.wikipedia.org/wiki/Front-end_and_back-endhttp://en.wikipedia.org/wiki/Hierarchical_internetworking_modelhttp://en.wikipedia.org/wiki/Open_Services_Architecturehttp://en.wikipedia.org/wiki/Rich_Internet_applicationhttp://en.wikipedia.org/wiki/Application_serverhttp://en.wikipedia.org/wiki/Java_EEhttp://en.wikipedia.org/wiki/Java_EEhttp://en.wikipedia.org/wiki/ASP.NEThttp://en.wikipedia.org/wiki/PHPhttp://en.wikipedia.org/wiki/ColdFusionhttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Database_management_systemhttp://en.wikipedia.org/wiki/Relational_database_management_systemhttp://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=4http://en.wikipedia.org/wiki/Simple_Network_Management_Protocolhttp://en.wikipedia.org/wiki/CORBAhttp://en.wikipedia.org/wiki/Java_RMIhttp://en.wikipedia.org/wiki/.NET_Remotinghttp://en.wikipedia.org/wiki/Windows_Communication_Foundationhttp://en.wikipedia.org/wiki/Windows_Communication_Foundationhttp://en.wikipedia.org/wiki/Internet_sockethttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Web_servicehttp://en.wikipedia.org/wiki/Middlewarehttp://en.wikipedia.org/wiki/Cluster_(computing)http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=5http://en.wikipedia.org/wiki/Application_Response_Measurementhttp://en.wikipedia.org/wiki/APIhttp://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Multitier_architecture&action=edit&section=7http://en.wikipedia.org/wiki/Client%E2%80%93server_modelhttp://en.wikipedia.org/wiki/Database-centric_architecturehttp://en.wikipedia.org/wiki/Front-end_and_back-endhttp://en.wikipedia.org/wiki/Hierarchical_internetworking_modelhttp://en.wikipedia.org/wiki/Open_Services_Architecturehttp://en.wikipedia.org/wiki/Rich_Internet_application

8/3/2019 2 tirear

7/7

Service layer

Web application

Load balancing (computing)

Multilayered architecture

http://en.wikipedia.org/wiki/Service_layerhttp://en.wikipedia.org/wiki/Web_applicationhttp://en.wikipedia.org/wiki/Load_balancing_(computing)http://en.wikipedia.org/wiki/Multilayered_architecturehttp://en.wikipedia.org/wiki/Service_layerhttp://en.wikipedia.org/wiki/Web_applicationhttp://en.wikipedia.org/wiki/Load_balancing_(computing)http://en.wikipedia.org/wiki/Multilayered_architecture