In this paper, we propose a system-level approach for verifying the safety of systems combining a continuoustime physical system with a discrete-time neural network based controller. We define a generic modelling approach and an associated reachability analysis that soundly approximates the reachable states of the overall system. We illustrate our approach through a real-world use case.
Stateflow is a widely used modeling framework for embedded and cyberphysical systems where control software interacts with physical processes. In this work, we present a framework and a fully automated safety verification technique for Stateflow models. Our approach is two-folded: (i) we faithfully compile Stateflow models into hierarchical state machines, and (ii) we use automated logic-based verification engine to decide the validity of safety properties. The starting point of our approach is a denotational semantics of Stateflow. We propose a compilation process using continuation-passing style (CPS) denotational semantics. Our compilation technique preserves the structural and modal behavior of the system. The overall approach is implemented as an open source toolbox that can be integrated into the existing Mathworks Simulink/Stateflow modeling framework. We present preliminary experimental evaluations that illustrate the effectiveness of our approach in code generation and safety verification of industrial scale Stateflow models.
This paper addresses the problem of querying several databases considered as a whole. Assuming that the different databases share a common data description language, the problem that arises is to consistently answer queries even if the database contents are contradictory. The main contribution of this paper is the specification of a query-evaluator for answering closed and open general queries addressed to several databases and for providing explanations about the results. For doing so, we first specify a query-evaluator, in logic, which assumes that the databases are propositional ones and do not contain disjunctions. Then we extend it to first-order databases defined by an extensional part (sets of positive or negative facts) and an intensional part (sets of first order clauses). We also show that the query-evaluator corresponds to a majority merging of the databases.scribes each data source as a view of the global schema) and the "Global-as-view" paradigm (which defines global relations as views of the local ones). See for instance [LEN 02] and [BRA 03] for more details.This present paper assumes that this problem is solved and that the different databases share a common data description language (i.e. a common sets of relations or predicate symbols). However, each databases may be associated with a proper set of rules (integrity constraints. . . ).Querying several conflicting databases 297 answer to "Is Paul registered in maths ?" will be Yes and it is Unchallenged. This explains that some databases contain information for proving that Paul is registered in maths and no database contains information for proving that he does not. The answer to "Is Phil registered in maths ?" will be Don't know, due to a lack of information, explaining that no database contains information for deciding which is the department where Phil is registered in. Finally, the answer to "Is Sandra registered in maths ?" will be something like We don't know due to a balanced inconsistency, explaining that the number of databases which agree on one department is equal to the number of databases which agree on another one. This paper is organized as follows. Section 2 presents the logical specification of a query-evaluator for answering atomic queries addressed to propositional databases which are sets of positive or negative propositional atoms. In section 3, we prove that this query evaluator corresponds to a majority method of merging propositional knowledge bases. This query-evaluator is then extended in section 4, so that we can ask queries written under conjunctive normal form. Section 5 extends the query evaluator to first order databases. Databases are there defined by an extensional part (sets of positive or negative facts) and an intensional part (sets of first order clauses) and are restricted so that they do not contain pure disjunctions. Section 6 details two examples. Finally, section 7 is devoted to a discussion. Specification of a query-evaluator for answering atomic queriesLet us assume a propositional language L, and sever...
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