Despite the well-known benefits of separation of concerns, and despite the presence of mechanisms to achieve separation of concerns in all modern software formalisms, software artifacts continue to exhibit properties associated with poor separation of concerns. Comprehensibility degrades over time; impact of change is high; reuse and traceability are limited. We have hypothesized that these limitations are largely cause by the "tyranny of the dominant decomposition:" existing languages and formalisms generally provide only one, "dominant" dimension along which to separate concerns-e.g., by object or by function. Achieving many software engineering goals depends on the ability to separate all concerns of importance. We therefore introduced the notion of multi-dimensional separation of concerns: simultaneous separation according to multiple, potentially overlapping concerns. This paper explores the structure of the space of concerns, to which we refer as hyperspace, partially formalizing our earlier model. We discuss how the model facilitates the identification and encapsulation of those portions of a system pertaining to a given concern, whether or not that concern is "dominant", and how it helps identify, introduce, change and remove concerns during evolution. We also show how this approach promotes two crucial aspects of evolvability: traceability and limited impact of change.
By: Harold Ossher, Peri Tarr
Published in: RC21452 in 1999
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