Kind Of Nondeterminism Research Articles

The Right Kind of Non-Determinism: Using Concurrency to Verify C Programs with Underspecified Semantics

We present a novel and well automatable approach to formal verification of C programs with underspecified semantics, i.e., a language semantics that leaves open the order of certain evaluations. First, we reduce this problem to non-determinism of concurrent systems, automatically extracting a distributed Active Object model from underspecified, sequential C code. This translation process provides a fully formal semantics for the considered C subset. In the extracted model every non-deterministic choice corresponds to one possible evaluation order. This step also automatically translates specifications in the ANSI/ISO C Specification Language (ACSL) into method contracts and object invariants for Active Objects. We then perform verification on the specified Active Objects model, using the Crowbar theorem prover, which verifies the extracted model with respect to the translated specification and ensures the original property of the C code for all possible evaluation orders. By using model extraction, we can use standard tools, without designing a new complex program logic to deal with underspecification. The case study used is highly underspecified and cannot be handled correctly by existing tools for C.

Teaching Nondeterminism Through Programming

Nondeterminism (ND) is a fundamental concept in computer science, and comes in two main flavors. One is the kind of ND that appears in automata theory and formal languages, and is the one that students are usually introduced to. It is known to be hard to teach. We present here a study, in which we introduced students to the second kind of ND, which we term opera- tive. This kind of ND is quite different from the first one. It appears in nondeterministic program - ming languages and in the context of concurrent and distributed programming. We study how high-school students understand operative ND after learning the nondeterministic programming language of live sequence charts (LSC). To assess students' learning, we used a two-dimensional taxonomy that is based upon the SOLO and the Bloom taxonomies. Our findings show that after a semestrial course on LSC, high-school students with no previous experience with ND of either type, understood operative ND on a level that allowed them to create and execute programs that included nondeterminism on various levels and in various degrees of complexity. We believe that it is important to expose students to the two types of ND, especially as ND has become a very prominent characteristic of computerized systems. Our findings suggest that students can reach a significant understanding of operative ND when the concept is introduced in the context of a programming course.

Fault Detection by Labeled Petri Nets in Centralized and Distributed Approaches

This paper addresses the problem of online fault detection and diagnosis in discrete event systems modeled by labeled Petri nets and using Integer Linear Programming Problem (ILPP) solutions. In particular, unobservable (silent) transitions model faults and both observable and unobservable transitions model the nominal system behavior. Furthermore, observable transitions exhibit a kind of non determinism since several different transitions may share the same event label. This paper proposes two diagnosers that work in two different system settings. The first one is a centralized fault detection strategy: the diagnoser waits for an observable event and an algorithm defines and solves some ILPPs to decide whether the system behavior is normal or may exhibit some faults. In the second setting, the system consists of a set of interacting PN modules and each module is monitored by a diagnoser that has local information on the module structure. Moreover, each diagnoser observes and detects the faults of the module it is attached to and shares information in some of its places that are shared with other modules of the system. Some case studies show the two different approaches and point out the peculiarities of the proposed strategies.

Multiparty interactions for interprocess communication and synchronization

The authors consider the essential properties of a multiparty interaction construct which serves as a primitive for interprocess communication and synchronization in distributed programs. It is claimed that more general constructs, which violate the suggested properties, are appropriate for abstraction but should not be seen as a communication primitive, and that both facilities are needed. Several acceptability criteria are posed for multiparty interactions, and various possibilities for constructs satisfying these criteria are presented. These include introducing a novel kind of nondeterminism within the assignments of an interaction, weakening the synchronization among the participants in an interaction, and varying the number of participants in order to provide a high-level treatment of fault tolerance. >