Two birds with one stone: Understanding 3-tier client/server architectures

Here we will use conceptual models to illustrate a couple major principles of software architecture. By now you should be getting a feel for what a sentence like this means. If you don't please make a comment here. No question is a silly one and we all benefit from the open airing of questions and concerns.

To review, a conceptual model is nothing more than a prototypical drawing representing an actual implementation of something (in our case a software system). Just as related-but-distinct plans are drawn up by architects and engineers for each element in the building of a new facility (the plumbing & heating specs, the architectural drawing, health & safety guidelines, the regulation and compliance measures, the electrical system, and so on), a different conceptual model can be drawn for all the different ways in which a system might be viewed (a process view, data view, network view, a user-interface view, etc...). In the process of designing, troubleshooting, or just discussing an application, each specific model may be used and "drawn" in the abstract to hide irrelevant details which would make it impossible to focus on a specific part of the design. The implementation of a software system is both designed and built upon an architecture. And hopefully that architecture is based on sound principles which give our creation distinct advantages such as quality and strength, cost-effectiveness, performance, ease-of-use, flexibility, scalability, and interoperability.

Here, using conceptual models, we take a closer look at two important and interrelated principles of software design: client/server and 3-tier architectures.

Both the client/server and 3-tier model have become central concepts of computer networking.  Here are some pointers on the 3-tier client/server architecture which identify the key characteristics of both.   

Remember a client/server architecture refers to a resource sharing strategy whereby one component, a server, provides specialized services on an as needed basis to other components, clients.

A three-tier architecture is one that groups the components within a system by function in three standard groupings:  the presentation layer as it's called which consists of components which manage  user interactions, the application layer which consists of components which manage the overal flow and control of the system and its components, and the data layer which is dedicated to managing the data which is needed by and supports the system.

Here are some examples of the two architectures co-existing.

By now you may be noticing....the principles of modularity, in large part, are the same that make the 3-tier client/server architecture so effective. Separating components of an application by their "class" enhances the application's scalability and flexibility. It makes it easier to manage as it allows the components to worry only about specialized tasks. So the people that look after the pieces also can worry only about their specialized task. Overall this makes for more stable, reliable, and reusable software. And given that we're talking about distributed software - that which is engaged and deployed using components which may be spread all over the network this separation is especially efficient - it makes for good use of network resources.

The Web itself is designed on a client/server architecture and most web-based applications use a 3-tier approach.

This post shows a three-tier architecture in the form of a web-based commerce application.