The New Three-Tier Application

In the beginning (that is, the 90’s), developers created the three-tier application. Per Martin Fowler, these tiers were the data source tier, managing persistent data, the domain tier, implementing the application’s primary business logic, and the presentation tier, handling the interaction between the user and the software. The motivation for this separation is as relevant today as it was then: to improve modularity and allow different components of the system to be developed relatively independently. Of course, application architecture has evolved greatly since the 90's. The first big change was in the presentation tier. While most applications once used native clients or the terminal as their interface, they’ve now mostly moved to a web interface. Thus, the presentation tier became the frontend and the domain tier became the backend: Over the last ~15 years, an even larger shift has occurred in the domain tier/backend. These used to be largely monolithic, implemented in a single ... Read full article.