The Web paradigm adds a whole new level of complexity to traditional application development. The phrase “You’ve got just 15 seconds to grab a user’s attention” is fast becoming a cliché, but it really sums up the idea. You’re no longer just creating an application, but a commercial or a TV show, and the user has his or her hand on the remote. It’s called surfing the Web for a reason. As a developer, you need to be keenly aware of the impact of architectural and implementation decisions on application performance and scalability. With this technology, as we are discovering, we are still dealing with a client/server model.

The Importance of Protocols
Have you ever seen a diplomatic meeting on a news report? Usually these events are very formal affairs with rules that were clearly defined beforehand. For diplomats, protocol is everything. It specifies the ceremony and etiquette and generally governs every aspect of interaction between nations. In short, it’s all about communication. For standards-based communication, protocols are everything as well. Internet protocols are agreed-upon standards for exchanging data between networks on diverse platforms and different environments.

Although understanding the entire network model is important, you’ll spend most of your time as a Web developer using the application-level protocols, such as Hypertext Transfer Protocol.

Hypertext Transfer Protocol
HTTP is known as a stateless protocol. It’s also one of the most highly used protocols in the process/application layer. Using HTTP for communication is normally divided into two parts: a request by the browser (or other client) to a server for information and a response by the server fulfilling the client request. This flow should be familiar to you because it resembles the client/server model with which we are all familiar.

HTTP uses Uniform Resource Locators (URLs) to assist in locating documents on Web servers. A URL is associated with a lower-level IP address and can be thought of as a human-readable way to access resources. We’ll explore how the two identifiers are resolved later. For now, let’s focus on the URL and its successive elements.

Download pdf Introduction to Web Application Development