The World Wide Web has become a ubiquitous part of modern life. Correspondingly, web development is a burgeoning industry. Web development differs from traditional software development in several profound ways.
A complex web site can be made up of several different pages, whose content can be generated from many different files. Content can be divided up among the files in an infinite number of ways by a web developer who writes the code in the files that when processed by the web server and displayed in a browser results in the page a viewer sees. As the web server processes the files, it frequently generates additional content along the way. A few lines of code processed by the web server can be responsible for the generation of hundreds of lines of code in the final web page. When a client makes a request to a web server, the web server determines what files compose the response, assembles them into a single file, and then sends the response back to the client. After a browser has loaded the documents received from the web server into the browser, a scripting language that adds interactive features to the web page may add, delete, or modify contents in the document.
The way web processing works affects web development. For example, when a web developer wants to change part of a web site, the web developer has to know which of the many files at the web server associated with the web site is the file that has to be changed.