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Lesson 3Web models
ObjectiveVarious models/ helps understanding Web components

Tool for thought: the Web Interaction Model

Compare various models as aids in understanding the components of the Web.

What actually happens when you access a Web resource? A number of different models explain how particular elements of the Web work, but the Web Interaction Model illustrates how these complex processes work together. Whereas other models are effective at illustrating the way technologies work, the Web Interaction Model is especially effective at accounting for the dynamic interaction between the user (including users who design pages as well as the end user) and those complex technologies. Before learning the full implications of applying this model, however, it is useful to compare other Web models.

Tiered models

One common way of talking about Web applications is based on the idea of "tiers." Each tier represents a different component or location of hardware and software, with the number of tiers increasing to account for the increased complexity in the technologies.

Types of Models: 2-tier and 3-tier

The 2-tiered model, or front-end/back-end model, is used to differentiate users or clients (the front end) from the hardware and software sources which provide the information they seek (the back end). The 3-tier model represents greater complexity in client- server applications. The back end is broken out into the components (hardware or software) that are distributed across different servers or locations. For example, the 3-tier model enables separation of a Web server (tier 2) from a database that provides information for specific applications (tier 3).

The N-tier model

The N-tier model recognizes that there are often many more tiers than just the individual user and a Web server. Because Web transactions increasingly involve multiple software applications or databases hosted in multiple locations, this model allows for the most expansive illustration of back-end technologies.
The following SlideShow shows how, like building blocks, this model relies on the addition of tiers to illustrate the added software, hardware, and network components that are necessary for increasingly complex technologies:

  1. The front end (Tier 1) consist of the user's computer and software, and the back end (Tier 2) consists of a Web server
  2. The 3-tier model acknowledges more complexity than the 2-tier model. A typical example is the separation of a Web server from a database server that provides information for specific applications
  3. The N-tier model encompasses a full range of back-end complexities, including components such as routers and firewalls.
  4. This model is especially valid for e-commerce and business-to-business Web Applications
  5. While this model accounts for the many different servers and applications that are involved in organizing and providing content to the user

N-tier Models

Limitations of Tiered Models

Although these models are easy to understand, by focusing almost exclusively on the back end, they oversimplify the real interaction that occurs during a typical Web transaction. For example, many e-commerce applications involve multiple components and locations.
A sample e-commerce transaction may involve components such as a consumer's personal computer; a customer's Internet service provider's ( ISP) network and hardware; the e-commerce site's Web server, database, and wide area network; and middleware at the e-commerce site's Application Service Provide. In the next lesson, you will learn about the function of the Web Interaction Model.

Click the link below to explore your understanding of the tiered models.
Tiered Models