The complexity of the systems that software engineers build has continuously grown since the inception of the field. What has not changed is the engineers? mental capacity to operate on about seven distinct pieces of information at a time. Improvements like the widespread use of UML have led to more abstract software design activities, however the same cannot be said for reverse engineering activities. The well known concept assignment problem is still being solved at the line-by-line level of analyzing source code. The introduction of abstraction to the problem will allow the engineer to move farther away from the details of the system, increasing his ability to see the role that domain level concepts play in the system. In this paper we present a technique that facilitates filtering of classes from existing systems at the source level based on their relationship to the core concepts in the domain. This approach can simplify the process of reverse engineering and design recovery, as well as other activities that require a mapping to domain level concepts.