Web Applications and HTTP

What’s a web application?

Since we’re going to develop web applications, let’s first figure out what we mean by this term. A web application is a program that runs on a server and is accessible over the network via the HTTP protocol, usually in a web browser. For us, it’s a broad definition that includes websites, SaaS (software as a service) applications, social networks, and even the backends of mobile applications. It’s comprehensive because, as developers, we build all of these things similarly.

What’s HTTP?

The Hypertext Transfer Protocol (HTTP) is an application layer protocol for hypertext, aka the internet as we know it. It’s a stateless protocol designed to be human-readable and extensible.

Hypertext is text with hyperlinks that leads to other hypertext documents. We can also use it for formatted text and different content types, like images.

Here’s an example of how hypertext works in this lesson. Look at the address bar in there browser. There’s a page URL, something like https://www.educative.io/courses/developing-web-applications-with-php/mE98QZpVw19. When the browser tries to open this page, it uses the https (HTTP Secure) protocol to send a GET /courses/developing-web-applications-with-php/mE98QZpVw19 request to the server behind www.educative.io. The server returns a document with references to other files (like images, styles, and client-side scripts), and the browser loads them with separate HTTP requests. Responses to all these requests are composed into this page.