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Web Development usage

In the Web development field, three-tier is often used to refer to Websites, commonly Electronic commerce websites, which are built using three tiers:

1. A front end Web server serving static content


2. A middle dynamic content processing and generation level Application server, for example Java EE platform.


3. A back end Database, comprising both data sets and the Database management system or RDBMS software that manages and provides access to the data.

Three Tier Architecture (Linux journal) [1]

• Presentation services tier    Responsible for gathering information from the user, sending the user information to the business services for processing, receiving the results of the business services processing, and presenting those results to the user.



• Business services tier    Responsible for receiving input from the presentation tier, interacting with the data services to perform the business operations that the application was designed to automate (for example, income tax preparation, order processing, and so on), and sending the processed results to the presentation tier.



• Data services tier    Responsible for storage, retrieval, maintenance, and integrity of data.

The Web is a good example of where to apply the three-tier model. Application developers know little about the potential clients except that they have a near-universal interface: the Web browser. The middle tier accepts requests from clients, retrieves information from the back-end systems, processes the data, and forwards the results to the client. The client is relieved of a lot of work. Thin clients are a good fit in this model.

The middle tier may provide the following services:

• The code for the middle tier can exist on multiple application servers, all accepting requests from multiple users (via load-balancing switches) and all connecting with the back-end systems.



• Message queuing allows clients to interact asynchronously with the back-end servers. In other words, transactions don't need to follow a precisely timed flow. The client may need to wait for a message from the server.



• The middle-tier server can provide transaction monitoring, which tracks the order and events of an online exchange to ensure that everything is complete and handled correctly. If not, the transaction is backed out.



• Distributed object computing services in which application logic and/or data resides in objects that are made available through an ORB (object request broker). An ORB provides a sort of software bus through which objects on one system can make requests of objects on another system. See "Distributed Object Computing."

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3-Tier
Architecture

The 3-tier architecture overcomes the weaknesses
of the 2-tier and
client/server architectures. It contains a client workstation, a component
server, and a database server. The user interface is on the client side while
business logic and data management are in dedicated tiers. Business logic resides
on one machine where it can be easily managed. Successful implementation of a
3-tier architecture requires considerable
applied