In software development, the term architecture is used as a metaphor that’s analogous to the architecture of a building. If architecture is the process and product of planning, designing, and constructing buildings, software architecture is the process and product of planning, designing, and constructing a software system. In architecture, there are structures that are so commonly used that they’re given names like domes, columns, and arches. There are common patterns and structures in software architecture too; most web applications are structured based on the three-tier architecture.
The three-tier architecture is a multi-tier architecture or multi-layered architecture. You’ll commonly find these patterns in computer systems that involve clients and servers like the Internet. In multitiered systems, code is strategically partitioned into separate tiers so that, whenever developers need to modify an application, they’ll only have to work with one tier at a time instead of tearing apart and reworking the entire application. The three tiers of three-tier architecture are:
In web development, front end refers to the highest tier — the presentation tier — and back end refers to the lowest tier — the data tier.
For web applications, the front end is the content rendered by the browser. It’s the content that users can see and interact with. In other words, it’s the web page itself. Colloquially, back end is used to refer to everything else that’s not the front end — that is, the logic tier and data tier. Technically, the back end specifically refers to the data tier which is comprised of the database or file system where data is stored and the software that manages and provides access to the data. In web applications, the logic tier is made up of software that can process user input from the front end, retrieve data from the back end, and process that data so it can be displayed by the front end. For the rest of this course, we’ll use the colloquial definition of back end, the one that encapsulates both the logic and data tier.