The concept of having layers that make up your enterprise architecture is nothing new. Indeed, in IT we love to create layer diagrams anytime we want to simplify things that are complex.
In the world of SOA, layers take on not only logical but physical characteristics, working up from the macro layer, or enterprisewide, to the micro layer or domain/project-specfic. The idea is that services and information should be available at each layer, but the way you leverage services and protect services is a bit different.
From my days as contributing geek/editor at PC Magazine I'm reminded of the operating system testing we did in PC Labs, and the logical and physical layers that each operating system leveraged when utilizing a platform. Indeed, on the x86 these were noted as rings, where ring 0 was the most privileged -- the kernel, really -- and working out to rings 1 and 2 (the device drivers), then to ring 3 (the applications). I remember how only the best-tested operating system components could touch ring 0. One false move and the machine was locked up. I mean the kind of lock up where you need to remove power to reboot.
So, what does processor architecture have to do with enterprise architecture? The notion is that there is always a ring 0 of enterprise architecture, or those core services that are common to all within the enterprise and thus the most important, which is why they need to be managed very carefully and made secure. Moreover, they need to have the ability to scale and never, ever fail, else the entire enterprise locks up.
Working up from ring 0, you have rings 1 and 2, which are the services that are domain specific. Services that are rarely shared outside of the domain but are also dependent on services found at ring 0. For instance, an HR service for resume processing that also leverages a ring 0 service to validate address information, which is also leveraged by the sales department domain, the support department domain, and shipping and logistics department domain.
Ring 3 are the configurable solutions, such as orchestration layers, traditional process integration layers, composite applications, etc., where you turn the services into business solutions. Again, dependent on services at rings 0 – 2.
It's an interesting concept using processor architectures to figure out enterprise architecture, but there are indeed similarities. Just as a well-designed operating system will provide a stable platform for computing, so will a well-designed enterprise architecture/SOA.