The three-tier architecture has dominated application deployment for decades. Presentation Layer, Logic Layer, Data Layer - every application designer is fed this bag of chips again and again, till every other chip is forgotten. Most companies have rigid policies that ensure that this holy trinity of layers is hammered into every policy document and SOP. But... As is true of so many religions, this one is also a bit outdated (Microsoft has even discontinued that page in their architecture). The theory was that many presentation layers could reuse the same business logic (encapsulated neatly in a application layer) but in my many years of slaving at these things I've rarely seen an app layer used by anything more than a single presentation layer as part of a single application. Indeed, this model was created for the client-server world and should have been thrown out when the world moved on but it was what everyone knew in those days so it somehow made it to the web world. A wh