Toward a Reasoning Framework for Dependability

Architecting dependable systems is a daunting task since it requires trade-offs among attributes such as reliability with a precisely computed, ordinal value and attributes such as security whose value is neither precisely computed nor ordinal. Quality attribute driven architecture design [1] techniques rely on models of the attributes that provide values that can be compared and ranked. Qualitative modeling techniques hold promise for being able to model quality attributes such as confidentiality and integrity for which quantitative models do not exist, but which need to be compared against one another. In this position paper we present a sketch of our work in progress on a hybrid approach that blends quantitative and qualitative techniques to design a dependable system. We introduce a chain of existing architecture modeling tools and briefly describe how they can be integrated to support the development of a rigorous design.