Formal Computational Model Research Articles

Modeling decision-making biases

Human decision-making can be affected by cognitive biases, and outside observers can often detect biased decision-making in others. Accordingly, intelligent agents endowed with the computational equivalent of the human mind should be able to detect biased reasoning and help people to improve their decision-making in practical applications. We are modeling bias-detection functionalities in OntoAgent, a cognitively-inspired agent environment that supports the modeling of intelligent agents with a wide range of sophisticated functionalities, including semantically-oriented language processing, decision-making, learning and collaborating with people. Within OntoAgent, different aspects of agent functionality are described using microtheories that are realized as formal computational models. This paper presents the OntoAgent model that supports the automatic detection of decision-making biases, using clinical medicine as a sample application area. It shows how an intelligent agent serving as a clinician’s assistant can follow the doctor–patient interaction and warn the doctor if it appears that his own or the patient’s decisions might be unwittingly affected by biased reasoning.

Synthesizing Globally Asynchronous Locally Synchronous Systems With IEC 61499

The IEC 61499 standard defines a generic architecture for designing distributed industrial control systems based on function blocks. The standard, however, lacks a formal model of computation to describe the behavior of function block compositions. While various models have been prescribed in the literature to define the composite behavior on a single computational node, few have been proposed to directly address compositions in a distributed setting. This paper proposes a globally asynchronous locally synchronous (GALS) model for distributed function block systems. The model provides an abstract way to view communication between function blocks without implying yet any particular implementation. This abstraction can then be subsequently refined to obtain various implementations with different tradeoffs. We do so using an approach that is fully compatible with the standard's notion of communication function blocks, which abstract underlying communication mechanisms from the application. As a contribution, we have developed a compiler that automatically synthesizes separate programs for a given distributed function block system without needing any additional middleware or run-time environment to execute the resulting distributed code. The efficacy of the proposed approach is demonstrated through an industrial case study.

Formal Semantics, Compilation and Execution of the GALS Programming Language DSystemJ

The paper presents a programming language, DSystemJ, for dynamic distributed Globally Asynchronous Locally Synchronous (GALS) systems, its formal model of computation, formal syntax and semantics, its compilation and implementation. The language is aimed at dynamic distributed systems, which use socket based communication protocols for communicating between components. DSystemJ allows the creation and control at runtime of asynchronous processes called clock-domains, their mobility on a distributed execution platform, as well as the runtime reconfiguration of the system's functionality and topology. As DSystemJ is based on a GALS model of computation and has a formal semantics, it offers very safe mechanisms for implementation of distributed systems, as well as potential for their formal verification. The details and principles of its compilation, as well as its required runtime support are described. The runtime support is implemented in the SystemJ GALS language that can be considered as a static subset of DSystemJ.

Efficient Algorithms for Computing With Protein-Based Volumetric Memory Processors

With an ever increasing volume of digital data there is a huge increase in the demand for much faster, smaller, and denser storage technologies. Conventional 2-D (surface) storage/memory technologies may soon be replaced with much faster and denser 3-D volumetric (holographic) storage technologies. Photo sensitive protein bacteriorhodopsin has been proven to have great chemical, thermal, and holographic properties and is a good choice for both associative and volumetric memories. Associative memory systems have a wide range of practical applications. However, there is a lack of a formal computational model that can be used to analyze the performance of different algorithms on architectures that support associative memory. We first address this issue by defining a new computational model on protein-based associative memory processors. We also present and analyze algorithms for several fundamental problems on this new model. Secondly, we employ balanced modulated codes in volumetric memories to reduce the bit error rate and improve fidelity. Conventional coding schemes such as 6:8 coding, limit the size of the page to 8 bits and achieve a code rate (utility) of only 75%. As the technology matures we need efficient algorithms to produce these codes with better utility. In this paper, we address this problem and give algorithms that can generate these codes with superior utility.

Introducing Language Technology & Computational Linguistics in Bangladesh

Information technology should have much to offer linguistics not only through the opportunities offered by large-scale data analysis and the stimulus to develop formal computational models, but through the chance to use language in systems for automatic natural language processing. The paper discusses these possibilities in detail and then examines the actual work that has been done in Bangladesh. It is an evident that this has so far been primary research within a new field of Computational Linguistics (CL) which is largely motivated by the demands and interest of practical processing systems and that information technology has rather little influence on linguistics at large.

Design of Distributed Heterogeneous Embedded Systems in DDFCharts

The use of formal models of computation in dealing with increasing complexity of embedded systems design is gaining attention. A successful model of computation must be able to handle both control-dominated and data-dominated behaviors, which are most often simultaneously present in complex embedded systems. Besides behavioral heterogeneity, direct support for modeling distributed systems is also desirable, since an increasing number of embedded systems belong to this category. In this paper, we present distributed DFCharts (DDFCharts), a language based on a formal model that targets distributed heterogeneous embedded systems. Its top hierarchical level is made suitable to capture distributed systems. Behavioral heterogeneity is addressed by composing finite-state machines (FSMs) and synchronous dataflow graphs (SDFGs). We illustrate modeling in DDFCharts with practical examples and describe its implementation on heterogeneous target architecture.

Resourceable, retargetable, modular instruction selection using a machine-independent, type-based tiling of low-level intermediate code

We present a novel variation on the standard technique of selecting instructions by tiling an intermediate-code tree. Typical compilers use a different set of tiles for every target machine. By analyzing a formal model of machine-level computation, we have developed a single set of tiles that is machine-independent while retaining the expressive power of machine code. Using this tileset, we reduce the number of tilers required from one per machine to one per architectural family (e.g., register architecture or stack architecture). Because the tiler is the part of the instruction selector that is most difficult to reason about, our technique makes it possible to retarget an instruction selector with significantly less effort than standard techniques. Retargeting effort is further reduced by applying an earlier result which generates the machine-dependent implementation of our tileset automatically from a declarative description of instructions' semantics. Our design has the additional benefit of enabling modular reasoning about three aspects of code generation that are not typically separated: the semantics of the compiler's intermediate representation, the semantics of the target instruction set, and the techniques needed to generate good target code.

Naturalism and scientific creativity: new tools for analyzing science

The Author(s) 2011. This article is published with open access at Springerlink.com In the preface to Models of discovery and creativity, Thomas Nickles pitches the book as the continuation of a research program that began unofficially at a conference on scientific discovery in the late 1970’s. The project is defined by its interdisciplinary nature, applying the combined resources of philosophy, social science, and cognitive science to the complex issues surrounding scientific concepts, practice, and methodology. Nickles offers the current volume as an update on the status of the program. All aspects of the project are present in the collected papers, which showcase an impressive array of analytical skills and historical expertise. If read as a unified project, the aims of the contributors are extremely ambitious—the present volume suggests no less than an attempt to create a crossdisciplinary methodology for the analysis of scientific creativity and conceptual change. Analytical tools range from formal models of reasoning (Magnani, Sintonen), evolutionary computation (Nickles), and philosophical and cognitive theories of concepts (Brown, Nersessian); to detailed research into the daily experimental activities of scientists (Holmes), and analysis of personal cooperation and competition amongst researchers in contexts of discovery (Werner). The variety of scientific fields and episodes discussed borders on astounding, ranging from the discoveries of nuclear fission (Andersen) and messenger RNA (Darden), to the construction of concepts and proofs in geometry and algebra (Glas). At first glance, it would seem impossible that experts in such a variety of fields should be employing anything like a unified methodology, or approaching a unified goal. It might be suspected that the volume is simply a grouping of a variety of really independent projects analyzing science from the distinct fields of philosophy of science, cognitive science, and science studies. However, there is a shared

The Golden Ratio Encoder

This paper proposes a novel Nyquist-rate analog-to-digital (A/D) conversion algorithm which achieves exponential accuracy in the bit-rate despite using imperfect components. The proposed algorithm is based on a robust implementation of a beta-encoder with β = φ = (1 + √5)/2, the golden ratio. It was previously shown that beta-encoders can be implemented in such a way that their exponential accuracy is robust against threshold offsets in the quantizer element. This paper extends this result by allowing for imperfect analog multipliers with imprecise gain values as well. Furthermore, a formal computational model for algorithmic encoders and a general test bed for evaluating their robustness is proposed.

A Formal Model of Universal Algorithmic Assembly and Molecular Computation

In this paper, the author describes a systematic and general approach to nanostructure synthesis and control through autonomous molecular combinatory computing. Combinatory computing is based on simple network (graph) substitution operations, deriving from combinatory logic (Curry, Feys, & Craig, 1958), which are sufficient for any computation. When these operations are implemented by autonomous molecular processes, they provide a means for computing within supramolecular networks, which may be used to assemble these networks or control their behavior. Further, the Church-Rosser Theorem (Curry, Feys, & Craig, 1958) proves that substitutions may be performed in any order or in parallel without affecting the computational result; this is a very advantageous property for autonomous molecular computation. In addition to the theoretical foundations of molecular combinatory computing, the author discusses possible molecular implementations as well as accomplishments in the (simulated) synthesis of membranes, channels, nanotubes, and other nanostructures.

Implicational markedness and frequency in constraint-based computational models of phonological learning

This study examines the interacting roles of implicational markedness and frequency from the joint perspectives of formal linguistic theory, phonological acquisition and computational modeling. The hypothesis that child grammars are rankings of universal constraints, as in Optimality Theory (Prince & Smolensky, 1993/2004), that learning involves a gradual transition from an unmarked initial state to the target grammar, and that order of acquisition is guided by frequency, along the lines of Levelt, Schiller & Levelt (2000), is investigated. The study reviews empirical findings on syllable structure acquisition in Dutch, German, French and English, and presents novel findings on Polish. These comparisons reveal that, to the extent allowed by implicational markedness universals, frequency covaries with acquisition order across languages. From the computational perspective, the paper shows that interacting roles of markedness and frequency in a class of constraint-based phonological learning models embody this hypothesis, and their predictions are illustrated via computational simulation.

Multiprocessor SoC software design flows

Typical design flows supporting the software development for multiprocessor systems are based on a board support package and high-level programming interfaces. These software design flows fail to support critical design activities, such as design space exploration or software synthesis. One can observe, however, that design flows based on a formal model of computation can overcome these limitations. In this article, we analyze the major challenges in multiprocessor software development and present a taxonomy of software design flows based on this analysis. Afterwards, we focus on design flows based on the Kahn process network (KPN) model of computation and elaborate on corresponding design automation techniques. We argue that the productivity of software developers and the quality of designs could be considerably increased by making use of these techniques.

A metamodel for the design of polychronous systems

This article presents the development of a metamodel and an open-source design environment for the synchronous language S ignal in the G me and Eclipse frameworks. This environment is intended to be used as a pivot modeling tool for a customized, aspect-oriented and application-driven, computer-aided engineering of embedded systems starting from multiple and heterogeneous initial specifications. The metamodel, called S ignalM eta, is defined on top of the design workbench P olychrony, which is dedicated to S ignal programming. Automated transformations are defined and implemented in order to produce, analyze, statically verify and model-check programs obtained from high-level models. The proposed approach promotes model-driven engineering within a framework that strongly favors formal validation. It aims at significantly decreasing design costs while improving the quality of systems. We demonstrate the agility of this approach by considering the design of both control-oriented and avionic systems. We start with an implementation of core polychronous 1 From the Greek words poly and chronos: multiple and time 1 data-flow concepts in G me and show the ease of its modular extension with application-specific concepts such as mode automata or integrated modular avionics concepts. This work is the first attempt to generalize the formal model of computation and the design philosophy of P olychrony.

RecDEVS: A Comprehensive Model of Computation for Dynamically Reconfigurable Hardware Systems

This paper introduces a novel formal model of computation denoted as RecDEVS. It is targeted to the development of dynamically reconfigurable hardware systems, a domain that still misses a formal design methodology. RecDEVS supports the description of hardware reconfiguration as a native part of a system model and thus can be used as a foundation of new design methodologies. Reconfiguration is addressed by means of a small set of reconfiguration commands and a dedicated executive component. Special care has been taken to support the flexible communication network of dynamically changeable hardware structures. We describe how RecDEVS benefits from the Dynamic Structure Discrete Event Specified Systems (DSDEVS) model that has been generalized. To illustrate the feasibility of the proposed approach the implementation of RecDEVS inside on top of SystemC based simulation engine is demonstrated.

Online processing of acoustic cues used in speech perception: Comparing statistical and neural network models.

Most phonological contrasts are signaled by multiple acoustic cues, yet it is unclear how these cues are combined during speech perception. Formal computational modeling offers a useful tool for studying this process. Two computational approaches are presented here. The first is a mixture of Gaussians (MOG) model that forms categories and combines cues based on their statistical distributions [Toscano and McMurray, Proceedings of the Cognitive Science Society (2008)]. The second is a neural network model that combines statistical learning and dynamic online processing [McMurray and Spivey, Proceedings of the Chicago Linguistic Society (1999)]. Both the MOG and the network use the statistical distributions of speech sounds to form categories. The MOG offers transparency in that its categories correspond directly to distributional statistics measured from phonetic data. However, it does not capture the online processing observed in behavioral experiments that suggest that the speech system makes preliminary commitments before all cues are available [McMurray, Clayards, Tanenhaus, and Aslin (submitted)]. The network offers an approach that may allow us to observe this processing. Thus, while the MOG may better clarify the relationship between acoustics and phonological categories, the network may better model the process of speech perception. [Work supported by NIH.]

Formalization of the ad hominem argumentation scheme

In this paper, several examples from the literature, and one central new one, are used as case studies of texts of discourse containing an argumentation scheme that has now been widely investigated in literature on argumentation. Argumentation schemes represent common patterns of reasoning used in everyday conversational discourse. The most typical ones represent defeasible arguments based on nonmonotonic reasoning. Each scheme has a matching set of critical questions used to evaluate a particular argument fitting that scheme. The project is to study how to build a formal computational model of this scheme for the circumstantial ad hominem argument using argumentation tools and systems developed in artificial intelligence. It is shown how the formalization built using these tools is applicable to the tasks of identification, analysis and evaluation of the central case studied. One important implication of the work is that it provides a foundational basis for showing how other argumentation schemes can be formalized.

Proving Correctness of an Efficient Abstraction for Interrupt Handling

This paper presents an approach to the efficient abstraction of interrupt handling in microcontroller systems. Such systems usually operate in uncertain environments, giving rise to a high degree of nondeterminism in the corresponding formal models, which in turn aggravates the state explosion problem. Careful handling of nondeterminism is therefore crucial for obtaining efficient model checking tools. Here, we support this goal by developing a formal computation model and an abstraction method, called interrupt nondeterminism, which instantiates nondeterministic values only if and when this is required by the application code. It is shown how this symbolic technique can be integrated into our explicit CTL model checking tool [mc]square by introducing lazy states. A lazy state consists of explicit and symbolic parts and therefore, represents several concrete states. With regard to interrupt handling, we also give a simulation relation between the concrete and the abstract state space, thus establishing the correctness of our technique. Furthermore, a case study is presented in which three different programs are used to demonstrate the effectiveness of our method.

A Rapid Prototyping Tool for Embedded, Real-Time Hierarchical Control Systems

Laboratory Virtual Instrumentation and Engineering Workbench (LabVIEW) is a graphical programming tool based on the dataflow language G. Recently, runtime support for a hard real-time environment has become available for LabVIEW, which makes it an option for embedded systems prototyping. Due to its characteristics, the environment presents itself as an ideal tool for both the design and implementation of embedded software. In this paper, we study the design and implementation of embedded software by using G as the specification language and the LabVIEW RT real-time platform. One of the main advantages of this approach is that the environment leads itself to a very smooth transition from design to implementation, allowing for powerful cosimulation strategies (e.g., hardware in the loop, runtime modeling). We characterize the semantics and formal model of computation of G. We compare it to other models of computation and develop design rules and algorithms to propose sound embedded design in the language. We investigate the specification and mapping of hierarchical control systems in LabVIEW and G. Finally, we describe the development of a state-of-the-art embedded motion control system using LabVIEW as the specification, simulation and implementation tool, using the proposed design principles. The solution is state-of-the-art in terms of flexibility and control performance.

Automated Integration of Dedicated Hardwired IP Cores in Heterogeneous MPSoCs Designed with ESPAM

This paper presents a methodology and techniques for automated integration of dedicated hardwired (HW) IP cores into heterogeneous multiprocessor systems. We propose an IP core integration approach based on an HW module generation that consists of a wrapper around a predefined IP core. This approach has been implemented in a tool called ESPAM for automated multiprocessor system design, programming, and implementation. In order to keep high performance of the integrated IP cores, the structure of the IP core wrapper is devised in a way that adequately represents and efficiently implements the main characteristics of the formal model of computation, namely, Kahn process networks, we use as an underlying programming model in ESPAM. We present details about the structure of the HW module, the supported types of IP cores, and the minimum interfaces these IP cores have to provide in order to allow automated integration in heterogeneous multiprocessor systems generated by ESPAM. The ESPAM design flow, the multiprocessor platforms we consider, and the underlying programming (KPN) model are introduced as well. Furthermore, we present the efficiency of our approach by applying our methodology and ESPAM tool to automatically generate, implement, and program heterogeneous multiprocessor systems that integrate dedicated IP cores and execute real-life applications.

Why do faultlines matter? A computational model of how strong demographic faultlines undermine team cohesion

Lau and Murnighan (LM) suggested that strong demographic faultlines threaten team cohesion and reduce consensus. However, it remains unclear which assumptions are exactly needed to derive faultline effects. We propose a formal computational model of the effects of faultlines that uses four elementary social mechanisms, social influence, rejection, homophily and heterophobia. We show that our model is consistent with the central hypotheses of LM’s theory. We also find that negative effects of faultlines can be derived even when – unlike LM – we assume that initially there is no correlation between the demographic characteristics and the opinions of team members.