TLA+ Model Checking Made Symbolic
By Igor Konnov
Igor Konnov is a senior research scientist at Interchain Foundation. He is developing model checking techniques for parameterized and fault-tolerant distributed algorithms. He is a co-PI in the project “APALACHE: Abstraction-based Parameterized Model Checker" funded by Vienna Science and Technology Fund (WWTF). Before joining Interchain Foundation, Igor Konnov worked as a researcher at Inria Nancy (France) and as a postdoc at TU Wien (Austria). He received his MSc and PhD in Applied Mathematics and Computer Science from Lomonosov Moscow State University (Russia).
TLA+ is a language for formal specification of all kinds of computer systems. System designers use this language to specify concurrent, distributed, and fault tolerant protocols, which are traditionally presented in pseudo-code. TLA+ is extremely concise yet expressive: The language primitives include Booleans, integers, functions, tuples, records, sequences, and sets thereof, which can be also nested. This is probably why the only model checker for TLA+ (called TLC) relies on explicit enumeration of values and states.
In this paper, we present APALACHE – a first symbolic model checker for TLA+. Like TLC, it assumes that all specification parameters are fixed and all states are finite structures. Unlike TLC, APALACHE translates the underlying transition relation into quantifier-free SMT constraints, which allows us to exploit the power of SMT solvers. Designing this translation is the central challenge that we address in this paper. Our experiments show that APALACHE outperforms TLC on examples with large state spaces.