Multi-dimensional Separation of Concerns in Hyperspace Multi-dimensional Separation of Concerns in Hyperspace

LIMITED DISTRIBUTION NOTICE This report has been submitted for publication outside of IBM and will probably be copyrighted if accepted for publication. It has been issued as a Research Report for early dissemination of its contents. In view of the transfer of copyright to the outside publisher, its distribution outside of IBM prior to publication should be limited to peer communications and speciic requests. After outside publication, requests should be lled only by reprints or legally obtained copies of the article (e.g., payment of royalties). Copies may be requested from IBM T.J. Abstract Despite the well-known beneets 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 caused by the \tyranny of the dominant decompo-sition:" 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 identiication 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.