> OSI I understand OSI, but it's not a useful model in this circumstance, because it draws no distinction between the HTTP layer and the business logic served

> OSI I understand OSI, but it's not a useful model in this circumstance, because it draws no distinction between the HTTP layer and the business logic served over HTTP. The complexities of that interface is what we're talking about. > HTTP status codes reflect the result of the HTTP request itself, not the next application in the chain, if one exists. Let's say I request /robotz.txt and I get 404 Not Found. How do you maintain that 404 is a result of "the HTTP request itself" and not the HTTP server handing the request to the component that looks on the filesystem (or in the cache, or in MongoDB, or...) and not finding the resource?