Continued my series of posts designed to cut through the sometimes obtuse terminology around AOP, this week I'll be defining "cross cutting concerns". Well, it's the title of the blog, so I guess I should explain it at some point, eh?

A cross-cutting concern is perhaps the "softest" of the terms, because it's more of an architectural concept than a technical one.

Basically, a cross-cutting concern is some piece of functionality that may not neatly fit in to normal object-oriented architecture, and most likely doesn't add business value or satisfy a requirement on its own (aka non-functional requirements). Logging is the most common example of a cross-cutting concern, because you might use logging in the UI layer, in the business logic, in the persistence layer, etc. Even in an individual layer, logging could be used across all classes/services, cutting through and crossing all the normal boundaries.

Other examples of cross-cutting concerns, which should come as no surprise if you're a regular reader: transactions, exception handling, INotifyPropertyChanged, authorization, caching, multi-threaded/asynchronous programming, auditing (very similar to logging). What else?