In general, nearly all e-commerce systems can be represented by the three-tier model as shown in figure 2.12:
This three-tier model has three main components, namely:
1) Client Side,
2) Service System, and
3) Backend System
The service system and the backend system are often called server side.
This three-tier model is a client/server-based computing system. The client side connects users to the system, the service system serves the users' requests, and the backend system supports the service system in fulfilling the users' requests (e.g., by providing the required data). From the business perspective, the client side provides the customer interface, the service system handles the business logic, and the backend system provides the necessary information to complete a transaction.
Figure 2.13 shows the typical architecture of a web-based e-commerce system in general. Referring to the three-tier model, the web server and the application server forms the service system, the web client or the web browser is client side, and database is backend system.
The web server is responsible for interacting with the web client as well as the application server and the backend system. The internet provides the communication platform for transferring information between the web client and the web server. The information transfer is governed by an application protocol called the Hypertext Transfer Protocol (HTTP). This is a simple request/response protocol for the web client and the web server to "talk" to each other. The web client issues a request to the web server and the web server returns a response to the web client.
To build the client side, one need a standard way to present text, images, graphics, and other multimedia information to users. For example, through the user interface, users can view product information and submit information to the web server.
In many cases, the web server's response is dynamic or is dependent on the user's input. For example, if a customer wants to search for some books, the web server's response will depend on the search criteria. To create a dynamic web page, the client's request invokes a program in the web server. In conjunction with the application server, the web server processes the client's request according to the program logic. In some cases, this may involve data retrieval from the database(s). After processing the client's request, the output will be returned to the client in the HTTP response message. The programs on the server side can be written in many languages.
HTTP is a simple request/response protocol, so it is stateless. In other words, a web server will not keep track of user state or user information. For example, a web server cannot know whether the current request is from a previous client or from a new client. In many e-commerce systems, knowing the user state is an important requirement. In technical terms, this is called session tracking.
In consumer-oriented systems, the client side is typically a user on a personal computer with a web browser to interact with the e-commerce system. In business oriented systems, the client side could be:
1) A user on a personal computer with a web browser to interact with the e- commerce system.
2) An organisational system that is capable of carrying-out purchasing and updating its own electronic documents and databases. Here there may be a direct connection between the client's organisational system and the seller's server-side system. Such communication is facilitated by electronic data interchange using business connectors.
The internet, itself, is a non-secure public network. Therefore, one need to protect the user against possible attacks from other users of the internet. Security is an important requirement in e-commerce.
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