The story of a web application 

Before we tackle the different use cases and the building blocks in the rest of the chapter, let's refresh the concepts of how a standard three-tier application would work. If you are wondering as to why this is important, it's because it provides an understanding of the building blocks that we will deal with in the latter part of the chapter. 

Most applications found today are web applications (applications accessible through a web browser). These range from relatively simple websites such as WordPress, to complicated systems such as Wolfram Alpha. These applications were traditionally 3-tier, comprising of a web-tier, an application-tier, and finally the database-tier. 

Now, let's take a look at an enterprise application, such as an employee management system. There are several products on the market, but essentially...