Salsa: Combining Constraint Solvers with BDDs for Automatic Invariant Checking

Abstract

Salsa is an invariant checker for specifications in SAL (the SCR Abstract Language). To establish a formula as an invariant without any user guidance, Salsa carries out an induction proof that utilizes tightly integrated decision procedures, currently a combination of BDD algorithms and a constraint solver for integer linear arithmetic, for discharging the verification conditions. The user interface of Salsa is designed to mimic the interfaces of model checkers; i.e., given a formula and a system description, Salsa either establishes the formula as an invariant of the system (but returns no proof) or provides a counterexample. In either case, the algorithm will terminate. Unlike model checkers, Salsa returns a state pair as a counterexample and not an execution sequence. Also, due to the incompleteness of induction, users must validate the counterexamples. The use of induction enables Salsa to combat the state explosion problem that plagues model checkers -it can handle specifications whose state spaces are too large for model checkers to analyze. Also, unlike general purpose theorem provers, Salsa concentrates on a single task and gains efficiency by employing a set of optimized heuristics.

Verified Software: The Real Grand Challenge

“…This initial study has shown that it is relatively straightforward to associate safety properties with generic modules that implement such architectural patterns. Proofs of these properties were carried out using the standard induction technique [7] using an assumption/guarantee proof system for compositional reasoning similar to [13]. Although we have automated the proofs of safety properties for concrete instances of an architectural pattern, an open problem is to develop automatic proof strategies for the generic case.…”

Model-Driven Agile Development of Reactive Multi-Agent Systems

“…The prototype Sage toolchain includes the Sage prototype tool set, sol2sal compiler, Salsa property checker [6], Sol compiler [4], and SINS middleware [5] which provides an execution environment for Sage agents. The prototype Sage tool set comprises a set of plug-ins to the Eclipse IDE (integrated development environment) and a set of external programs and scripts.…”

Generating optimized code from SCR specifications

“…The SCR toolset [10] provides a user-friendly approach to writing requirements specifications and a suite of analysis tools for analyzing them. The toolset includes a consistency checker [13], a simulator [12], a model checker [11], theorem provers [2,4], and an invariant generator [15,17].…”