# Cross-cutting concern

> (in Aspect-oriented programming) Cross-cutting concern

(in [Aspect-oriented programming](https://wiki.g15e.com/pages/Aspect-oriented%20programming.txt)) Cross-cutting concern

The concern that doesn't stay inside of any one module boundary such as:

- System-wide error-handling
- Contract enforcement (see [Contract-driven development](https://wiki.g15e.com/pages/Contract-driven%20development.txt))
- Distribution concerns
- Feature variations
- Context-sensitive behavior
- Persistence
- Testing

Cross-cutting concern is inherent in complex systems. But cross-cutting concerns have a clear purpose and a natural structure. Cross-cutting concern's natural structure is:

- Defined set of methods
- Module boundary crossings
- Points of resource utilization
- Lines of dataflow
- …

In <AOP>, we can use [aspects](https://wiki.g15e.com/pages/Aspect%20(AOP.txt)) to capture the structure of cross-cutting concerns explicitly in a modular way, linguistic and with tool support. Aspects are well modularized cross-cutting concerns.