Done well, separation of concerns can provide many soft-ware engineering benefits, including reduced complexity, im-proved reusability, and simpler evolution. The choice of boundaries for separate concerns depends on both require-ments on the system and on the kind(s) of decompositionand composition a given formalism supports. The predominant methodologies and formalisms available, however, support only orthogonal separations of concerns, along sdngle dimen-sions of composition and decomposition. These characteris-tics lead to a number of well-known and difficult problems. This paper describes a new paradigm for modeling and im-plementing software artifacts, one that permits separation of overlapping concerns along multiple dimensions of composi-tion and decomposition. This approach addresses numerous problems throughout the software lifecycle in achieving well-engineered, evolvable, flexible software artifacts and trace-ability across artifacts.

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