n-tier vs. n-layer

The man might be know his architecture, but his vocabulary needs work. Tier and layer are synonomous, logical and physical are not.

There are also often valid requirements for different physical tiers or layers, such as having multiple clients sharing the same database server. When implemented on a serparate machine, maintenance or downtime on the database need not affect the operation of clients.

I disagree on your vocab point - i think talking of a tier as being physical and a layer as logical helps to more clearly define a discussion on the topic.

You should read his business object book bro (highly recommended) - i think you will find that you are 'preaching to the choir'. :-P

In most cases Tier and Layers are synonymous, but there exists a subtle difference between both, Tier is the partitioning of the system like User, Business and Data. Where as layer is the partioning of the Tiers. For example an User Tier can consist of the Client Layer and a Presentation Layer (existing in the server).

Regardless of what terminology is used, separating code into different objects is preferred, while using multiple machines is not desireable because of the performance hit. Rockford has defined tiers as relating to machines and layers as code objects. Sounds good to me. Let's use them.