Abstract.We report on a model-based approach to system-software coengineering which is tailored to the specific characteristics of critical onboard systems for the aerospace domain. The approach is supported by a System-Level Integrated Modeling (SLIM) Language by which engineers are provided with convenient ways to describe nominal hardware and software operation, (probabilistic) faults and their propagation, error recovery, and degraded modes of operation.Correctness properties, safety guarantees, and performance and dependability requirements are given using property patterns which act as parameterized "templates" to the engineers and thus offer a comprehensible and easy-to-use framework for requirement specification. Instantiated properties are checked on the SLIM specification using state-of-the-art formal analysis techniques such as bounded SAT-based and symbolic model checking, and probabilistic variants thereof. The precise nature of these techniques together with the formal SLIM semantics yield a trustworthy modeling and analysis framework for system and software engineers supporting, among others, automated derivation of dynamic (i.e., randomly timed) fault trees, FMEA tables, assessment of FDIR, and automated derivation of observability requirements.
We present quantitative separation logic (QSL). In contrast to classical separation logic, QSL employs quantities which evaluate to real numbers instead of predicates which evaluate to Boolean values. The connectives of classical separation logic, separating conjunction and separating implication, are lifted from predicates to quantities. This extension is conservative: Both connectives are backward compatible to their classical analogs and obey the same laws, e.g. modus ponens, adjointness, etc. Furthermore, we develop a weakest precondition calculus for quantitative reasoning about probabilistic pointer programs in QSL. This calculus is a conservative extension of both Ishtiaq's, O'Hearn's and Reynolds' separation logic for heap-manipulating programs and Kozen's / McIver and Morgan's weakest preexpectations for probabilistic programs. Soundness is proven with respect to an operational semantics based on Markov decision processes. Our calculus preserves O'Hearn's frame rule, which enables local reasoning. We demonstrate that our calculus enables reasoning about quantities such as the probability of terminating with an empty heap, the probability of reaching a certain array permutation, or the expected length of a list.
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