(From aosd.net) A concern is an area of interest or focus in a system. Concerns are the primary criteria for decomposing software into smaller, more manageable and comprehensible parts that have meaning to a software engineer (see separation of concerns). Examples of concerns include requirements, use cases, features, data structures, quality-of-service issues, variants, intellectual property boundaries, collaborations, patterns and contracts. There are many formulations used to capture concerns as well-identified separate units, aspects are one such mechanism, that are tuned to capturing crosscutting concerns.