Declarative Programming Language Research Articles

Intrinsic Prioritization in Answer Set Programming Based on an Adapted Notion of Tolerance

Answer set programming (ASP) is a declarative programming language suited to solve complex combinatorial search problems. Prioritized ASP is the subdiscipline of ASP which aims at prioritizing the models (answer sets) of ASP programs. Common approaches to prioritized ASP require an additional input, sometimes expressed as special literals within the ASP program, that guides the prioritization of the answer sets. In this paper, to the best of our knowledge, we propose the first approach that is able to prioritize answer sets solely based on the original ASP program. For this, we adapt the notion of tolerance from conditional reasoning according to System Z and establish tolerance partitions of ASP programs which can be used for prioritization.

Optimizing Nested Recursive Queries

Datalog is a declarative programming language that has gained popularity in various domains due to its simplicity, expressiveness, and efficiency. But "pure" Datalog is limited to monotone queries, and cannot be used in most practical applications. For that reason, newer systems are relaxing the language by allowing non-monotone queries to be freely combined with recursion. But by departing from the elegant fixpoint semantics of pure datalog, these systems often result in inefficient query execution, for example they perform redundant computations, or use redundant storage. In this paper, we propose Temporel, a system that allows recursion to be freely combined with non-monotone operators. Temporel optimizes the program by compiling it into a novel intermediate representation that we call TempoDL. Our experimental results show that our system outperforms a state-of-the-art Datalog engine as well as a vectorized and a compiled in-memory database system for a wide range of applications from machine learning to graph processing.

CNL2ASP: Converting Controlled Natural Language Sentences into ASP

Abstract Answer set programming (ASP) is a popular declarative programming language for solving hard combinatorial problems. Although ASP has gained widespread acceptance in academic and industrial contexts, there are certain user groups who may find it more advantageous to employ a higher-level language that closely resembles natural language when specifying ASP programs. In this paper, we propose a novel tool, called CNL2ASP, for translating English sentences expressed in a controlled natural language (CNL) form into ASP. In particular, we first provide a definition of the type of sentences allowed by our CNL and their translation as ASP rules and then exemplify the usage of the CNL for the specification of both synthetic and real-world combinatorial problems. Finally, we report the results of an experimental analysis conducted on the real-world problems to compare the performance of automatically generated encodings with the ones written by ASP practitioners, showing that our tool can obtain satisfactory performance on these benchmarks.

Assessing the Usability of Two Declarative Programming Languages to Model Geometric Events

When space missions plan scientific actions for robotic spacecraft to execute, they frequently do so within a geometric context called an opportunity. Although there are geometric software libraries that let users write code to search for opportunities, they require knowledge of algorithms and imperative programming languages, which is a condition that might exclude a potentially large population of scientists. Additionally, there might be more user-friendly software systems for scientists to model and search for opportunities, but those might exclude other missions due to export concerns or an inability to maintain such software due to lack of staff or funding. To address these concerns, we designed two different computer languages to model opportunities. In this paper, we present these two languages, our study to evaluate their relative readability and usability, and results obtained in our research along with an interpretation of the same. The metric for this study has been a questionnaire with active exercises, statements with corresponding responses on a Likert scale, and open-ended questions to elicit qualitative responses. The study’s quantitative results provide us with relative and absolute quantification of the usability and readability of each language, while the study’s qualitative results help us direct future language design decisions.

Development of the concept for determining the level of critical business processes security

The development of technologies and computing resources not only expanded the spectrum of digital services in all areas of human activity, but also defined the spectrum of targeted cyber attacks. The object of the study is the process of ensuring the safety of critical business processes that ensure the continuity of production and/or functioning of the company/organization/enterprise as a whole. Targeted attacks are aimed at destroying not only the business structure, but also its individual components that determine critical business processes. Continuity of such business processes is a critical component of any company, organization or enterprise of any form of government, which critically affects the earning of profits or the organization of production processes. The proposed concept of determining the security level of critical business processes is based on the need to use multi-loop information protection systems. This allows to ensure the continuity of critical business processes through a timely objective assessment of the level of security and the timely formation of preventive measures. This approach is based on the proposed rules for determining the achievement of a given level of security, which are based on assessments of the integrity, availability and confidentiality of information arrays, as well as computer equipment in relation to various points of the organization's business processes. The use of threat integration on the internal and external contours of the protection system allows to ensure the necessary level of security and continuity of the production/technological process of critical business processes. The proposed practical implementation of the system security level assessment system in the declarative programming language Prolog, which allows to form requirements regarding the achievement of a given system security level depending on the state assessments of individual system components

Мобильный симулятор эхолота

A mobile application, designed to simulate real echo sounder, was developed at the Department of Information Technologies of the Saint Petersburg State University of Architecture and Civil Engineering (St. Petersburg, Russia). This application, potentially categorized as business software, can be used to test systems related to maritime navigation, as well as to create sea and river maps. The application is developed by C++ programming language using the cross-platform Qt library. The Graphic User Interface of the application is designed using the declarative programming language QML. The implementation of the mobile version of the application made it possible to refuse the use of additional communication devices to ensure communication between the simulator and the device under test.

Unifying Framework for Optimizations in Non-Boolean Formalisms

AbstractSearch-optimization problems are plentiful in scientific and engineering domains. Artificial intelligence (AI) has long contributed to the development of search algorithms and declarative programming languages geared toward solving and modeling search-optimization problems. Automated reasoning and knowledge representation are the subfields of AI that are particularly vested in these developments. Many popular automated reasoning paradigms provide users with languages supporting optimization statements. Recall integer linear programming, MaxSAT, optimization satisfiability modulo theory, (constraint) answer set programming. These paradigms vary significantly in their languages in ways they express quality conditions on computed solutions. Here we propose a unifying framework of so-called extended weight systems that eliminates syntactic distinctions between paradigms. They allow us to see essential similarities and differences between optimization statements provided by distinct automated reasoning languages. We also study formal properties of the proposed systems that immediately translate into formal properties of paradigms that can be captured within our framework.

A case study comparing static analysis tools for evaluating SwiftUI projects

Declarative programming languages such as SwiftUI have gained increasing relevance for user interface implementation in mobile applications. A tool for evaluating and improving the quality of such projects is static analysis (SA). This study compares the usefulness of two of the most popular SA tools (SonarQube and Codacy) for evaluating real-world SwiftUI projects. Moreover, it recommends setup and adjustments to promote SA tools for SwiftUI projects that can be extended to other languages.

Применение методов информационной инженерии для изменения структуры многоуровневых систем организационного управления

In this work the task is formulated and the method of reconfiguration of systems of organizational management on the basis of synthesis of the functional structure having an impact on an appearance of all system considerably defining an order of its functioning, integrating in a whole of means of technical and mathematical, program and information support is offered. The research objective consists in need of increase in effective management of organizational systems on the basis of complex development, implementation and application of funds of automated management of its elements. Expert systems on the basis of declarative programming languages are applied to synthesis of similar structures. Research methods. As the tool for definition of the knowledge base about the field of restructuring of structure of management calculation of expressions and language of a predicate logic, that is a logic theory of first order is used. Then, the problem of reconfiguration of hierarchical structure of management system can be presented doubly. First, as a problem of definition of the changes of the known rational hierarchical structure providing minimum loss from the arisen functional failures. Secondly, as a problem of creation of new rational structure which provides optimum use of the resources used in the course of achievement of definite purposes in the changing conditions. Results. As a result of a research, on the basis of de Morgan's law the factors influencing a system status of organizational management in general are defined. The necessary structure of solvable tasks of all hierarchical structure is defined by extent of influence of different factors on characteristics of structure of management. Conclusion. Work of the received expert system consists in consecutive execution or failure to follow rules and transition from one status to another. In case of an impasse the expert system gives the report in the form of requirements of alternative change of these or those rules (factors). New rules are remembered. Thus, the system of knowledge is increased.

Knowing when to ask: sound scheduling of name resolution in type checkers derived from declarative specifications

There is a large gap between the specification of type systems and the implementation of their type checkers, which impedes reasoning about the soundness of the type checker with respect to the specification. A vision to close this gap is to automatically obtain type checkers from declarative programming language specifications. This moves the burden of proving correctness from a case-by-case basis for concrete languages to a single correctness proof for the specification language. This vision is obstructed by an aspect common to all programming languages: name resolution. Naming and scoping are pervasive and complex aspects of the static semantics of programming languages. Implementations of type checkers for languages with name binding features such as modules, imports, classes, and inheritance interleave collection of binding information (i.e., declarations, scoping structure, and imports) and querying that information. This requires scheduling those two aspects in such a way that query answers are stable—i.e., they are computed only after all relevant binding structure has been collected. Type checkers for concrete languages accomplish stability using language-specific knowledge about the type system. In this paper we give a language-independent characterization of necessary and sufficient conditions to guarantee stability of name and type queries during type checking in terms of critical edges in an incomplete scope graph . We use critical edges to give a formal small-step operational semantics to a declarative specification language for type systems, that achieves soundness by delaying queries that may depend on missing information. This yields type checkers for the specified languages that are sound by construction—i.e., they schedule queries so that the answers are stable, and only accept programs that are name- and type-correct according to the declarative language specification. We implement this approach, and evaluate it against specifications of a small module and record language, as well as subsets of Java and Scala.

Arithmetics based on computability logic

This paper is a brief survey of number theories based on em computability logic (CoL) a game-semantically conceived logic of computational tasks of resources. Such theories, termed em clarithmetics, are conservative extensions of first-order Peano arithmetic. 
 
 The first section of the paper lays out the conceptual basis of CoL and describes the relevant fragment of its formal language, with so called parallel connectives, choice connectives and quantifiers, and blind quantifiers. Both syntactically and semantically, this is a conservative generalization of the language of classical logic. 
 
 Clarithmetics, based on the corresponding fragment of CoL in the same sense as Peano 
 arithmetic is based on classical logic, are discussed in the second section. The axioms and inference rules of the system of clarithmetic named ${\bf CLA11}$ are presented, and the main results on this system are stated: constructive soundness, extensional completeness, and intensional completeness. 
 
 
 In the final section two potential applications of clarithmetics are addressed: clarithmetics as declarative programming languages in an extreme sense, and as tools for separating computational complexity classes. When clarithmetics or similar CoL-based theories are viewed as programming languages, programming reduces to proof-search, as programs can be mechanically extracted from proofs; such programs also serves as their own formal verifications, thus fully neutralizing the notorious (and generally undecidable) program verification problem. The second application reduces the problem of separating various computational complexity classes to separating the corresponding versions of clarithmetic, the potential benefits of which stem from the belief that separating theories should generally be easier than separating complexity classes directly. 

Модели времени для сложных распределенных дискретных систем

The impetus for writing this article was the thesis about the inadequacy of using linearly-ordered time models in describing processes in complex discrete systems characterized by the presence of components with independent behavior between the moments of their interaction, with recursively defined, hierarchically organized, varying (dynamic) structure unlimited in complexity, and with non-deterministic behavior. The cause-and-effect relationships between possible events in a distributed multicomponent system leading to changes in its state determine, among other things, the minimally necessary partial order in the set of time instants corresponding to possible events in the system. The time universe is understood to mean the class of isomorphic finite partially-strictly ordered sets as a necessary basic formalism. The above-mentioned concept differs from other well-known formalizations (such as acyclic digraphs, Hasse diagrams, etc.) in that it uses a strictly partial order under the assumption that the set of simultaneous events in the system can be considered as one complex event. The presence of the above-mentioned features of complex systems generates the need to analyze the sets of time universes both in view of possible non-determinism in the behavior of systems and as a consequence of changes resulting from events associated with the system structure itself and the cause-and-effect relationships acting in it. The problem of developing a constructive description—with different degrees of complexity—of time universe sets, primarily infinite ones, which is similar to specifying formal languages as sets of words in a certain alphabet. The authors have solved a similar problem in the theory of directed relationships - the basic formalism for constructing declarative programming languages using the network representation of directed relationships. The key point of such solution is to correctly define the operation of substituting a network into another network instead of some element thereof, which plays the role of entering the network variable into the network structure and has the same specifications as the substituted network. The T-network and T-network language notions introduced in the article, i.e., sets of T-networks, are used to constructively specify the sets of time universes in modeling parallel processes in systems. The main syntactic difference between T-networks and networks of directed relationships is the requirement that T-networks shall not contain cycles, which is ensured by fulfilling certain proposed restrictions posed to network components. The correctness of the substitution operation with respect to these restrictions is proven. The substitution operation can be used both for hierarchically constructing T-networks and for multivariate and recursive assignment of T-network sets. Application of the substitution operation for defining a representative class of context-free T-network languages using context-free T-network grammars is described. A simple grammar example describing the time model for parallel recursive calculation of a definite integral is given, and further research lines are pointed out.

An Operational Semantics for the Cognitive Architecture ACT-R and Its Translation to Constraint Handling Rules

Computational psychology has the aim to explain human cognition by computational models of cognitive processes. The cognitive architecture Adaptive Control of Thought--Rational (ACT-R) is popular to develop such models. Although ACT-R has a well-defined psychological theory and has been used to explain many cognitive processes, there are two problems that make it hard to reason formally about its cognitive models: First, ACT-R lacks a computational formalization of its underlying production rule system, and, second, there are many different implementations and extensions of ACT-R with many technical artifacts complicating formal reasoning even more. This article describes a formal operational semantics—the very abstract semantics —that abstracts from as many technical details as possible, keeping it open to extensions and different implementations of the ACT-R theory. In a second step, this semantics is refined to define some of its abstract features that are found in many implementations of ACT-R—called the abstract semantics . It concentrates on the procedural core of ACT-R and is suitable for analysis of the general transition system, since it still abstracts from details like timing, the sub-symbolic layer of ACT-R or conflict resolution. Furthermore, a translation of ACT-R models to the declarative programming language Constraint Handling Rules (CHR) is defined. This makes the abstract semantics an executable specification of ACT-R. CHR has been used successfully to embed other rule-based formalisms like graph transformation systems or functional programming. There are many theoretical results and practical tools that support formal reasoning about and analysis of CHR programs. The translation of ACT-R models to CHR is proven sound and complete w.r.t. the abstract operational semantics of ACT-R. This paves the way to analysis of ACT-R models through CHR analysis results and tools. Therefore, to the best of our knowledge, our abstract semantics is the first abstract formulation of ACT-R suitable for both analysis and execution.

Parallelism, concurrency and distribution in constraint handling rules: A survey

AbstractConstraint Handling Rules (CHR) is both an effective concurrent declarative programming language and a versatile computational logic formalism. In CHR, guarded reactive rules rewrite a multi-set of constraints. Concurrency is inherent, since rules can be applied to the constraints in parallel. In this comprehensive survey, we give an overview of the concurrent, parallel as well as distributed CHR semantics, standard and more exotic, that have been proposed over the years at various levels of refinement. These semantics range from the abstract to the concrete. They are related by formal soundness results. Their correctness is proven as a correspondence between parallel and sequential computations. On the more practical side, we present common concise example CHR programs that have been widely used in experiments and benchmarks. We review parallel and distributed CHR implementations in software as well as hardware. The experimental results obtained show a parallel speed-up for unmodified sequential CHR programs. The software implementations are available online for free download and we give the web links. Due to its high level of abstraction, the CHR formalism can also be used to implement and analyse models for concurrency. To this end, the Software Transaction Model, the Actor Model, Colored Petri Nets and the Join-Calculus have been faithfully encoded in CHR. Finally, we identify and discuss commonalities of the approaches surveyed and indicate what problems are left open for future research.

Knowledge-driven computational modeling in Alzheimer's disease research: Current state and future trends

Neurodegenerative diseases such as Alzheimer's disease (AD) follow a slowly progressing dysfunctional trajectory, with a large presymptomatic component and many comorbidities. Using preclinical models and large-scale omics studies ranging from genetics to imaging, a large number of processes that might be involved in AD pathology at different stages and levels have been identified. The sheer number of putative hypotheses makes it almost impossible to estimate their contribution to the clinical outcome and to develop a comprehensive view on the pathological processes driving the clinical phenotype. Traditionally, bioinformatics approaches have provided correlations and associations between processes and phenotypes. Focusing on causality, a new breed of advanced and more quantitative modeling approaches that use formalized domain expertise offer new opportunities to integrate these different modalities and outline possible paths toward new therapeutic interventions. This article reviews three different computational approaches and their possible complementarities. Process algebras, implemented using declarative programming languages such as Maude, facilitate simulation and analysis of complicated biological processes on a comprehensive but coarse-grained level. A model-driven Integration of Data and Knowledge, based on the OpenBEL platform and using reverse causative reasoning and network jump analysis, can generate mechanistic knowledge and a new, mechanism-based taxonomy of disease. Finally, Quantitative Systems Pharmacology is based on formalized implementation of domain expertise in a more fine-grained, mechanism-driven, quantitative, and predictive humanized computer model. We propose a strategy to combine the strengths of these individual approaches for developing powerful modeling methodologies that can provide actionable knowledge for rational development of preventive and therapeutic interventions. Development of these computational approaches is likely to be required for further progress in understanding and treating AD.

A qualitative assessment of $$\alpha $$ α Rby in the perspective of the supervisory control theory

It becomes more and more evident today that SAT-solving approaches have the potential to verify properties and synthesize supervisors of controlled systems described with a high level of abstraction. Such approaches can be particularly appropriate when engineers give more importance to decentralized, hierarchical, and parameterized control paradigms than to centralized ones in the design of systems composed of multiple small agents. One advantage of declarative programming languages, such as relational logic, in specifying control problems, including their underlying properties and reasoning methods, is their proximity to the mathematical objects used in the formulation of the theory itself, which allows for implementing new fragments of it faster. The disadvantage is, however, that SAT-solving approaches do not lend themselves to efficient calculations of auxiliary objects involved in some control problems, even if they can be described with the logic at hand. In some cases, the latter is not sufficiently powerful to express the entire solution logically. Such difficulties can be circumvented with $$\alpha {\textsc {Rby}}$$ , a fusion of Alloy and Ruby. Based on earlier experiments conducted with Alloy, this paper provides a qualitative assessment of $$\alpha {\textsc {Rby}}$$ and reports on the results of new experiments with two fragments of the supervisory control theory: state-based control and decentralized control.

Dynamically Constructed (PO)MDPs for Adaptive Robot Planning

To operate in human-robot coexisting environments, intelligent robots need to simultaneously reason with commonsense knowledge and plan under uncertainty. Markov decision processes (MDPs) and partially observable MDPs (POMDPs), are good at planning under uncertainty toward maximizing long-term rewards; P-LOG, a declarative programming language under Answer Set semantics, is strong in commonsense reasoning. In this paper, we present a novel algorithm called iCORPP to dynamically reason about, and construct (PO)MDPs using P-LOG. iCORPP successfully shields exogenous domain attributes from (PO)MDPs, which limits computational complexity and enables (PO)MDPs to adapt to the value changes these attributes produce. We conduct a number of experimental trials using two example problems in simulation and demonstrate iCORPP on a real robot. Results show significant improvements compared to competitive baselines.

A Typeful Integration of SQL into Curry

We present an extension of the declarative programming language Curry to support the access to data stored in relational databases via SQL. Since Curry is statically typed, our emphasis on this SQL integration is on type safety. Our extension respects the type system of Curry so that run-time errors due to ill-typed data are avoided. This is obtained by preprocessing SQL statements at compile time and translating them into type-safe database access operations. As a consequence, the type checker of the Curry system can spot type errors in SQL statements at compile time. To generate appropriately typed access operations, the preprocessor uses an entity-relationship (ER) model describing the structure of the relational data. In addition to standard SQL, SQL statements embedded in Curry can include program expressions and also relationships specified in the ER model. The latter feature is useful to avoid the error-prone use of foreign keys. As a result, our SQL integration supports a high-level and type-safe access to databases in Curry programs.

Extending multimedia languages to support multimodal user interactions

Historically, the Multimedia community research has focused on output modalities, through studies on timing and multimedia processing. The Multimodal Interaction community, on the other hand, has focused on user-generated modalities, through studies on Multimodal User Interfaces (MUI). In this paper, aiming to assist the development of multimedia applications with MUIs, we propose the integration of concepts from those two communities in a unique high-level programming framework. The framework integrates user modalities --both user-generated (e.g., speech, gestures) and user-consumed (e.g., audiovisual, haptic)-- in declarative programming languages for the specification of interactive multimedia applications. To illustrate our approach, we instantiate the framework in the NCL (Nested Context Language) multimedia language. NCL is the declarative language for developing interactive applications for Brazilian Digital TV and an ITU-T Recommendation for IPTV services. To help evaluate our approach, we discuss a usage scenario and implement it as an NCL application extended with the proposed multimodal features. Also, we compare the expressiveness of the multimodal NCL against existing multimedia and multimodal languages, for both input and output modalities.

Proceedings of the Workshop on Continuations

The notion of continuation is ubiquitous in many different areas of computer science, including systems programming, programming languages, algorithmics, semantics, logic, and constructive mathematics. In fact the concept of continuation nicely realizes sophisticated control mechanisms, which are widely used in a variety of applications. Since we cannot escape control features, it becomes a challenge to provide them with sound reasoning principles. Indeed there is much research activity on understanding, representing, and reasoning about elaborated non-local control structures, in particular in declarative programming languages such as functional and logic languages. The proceedings of the Workshop on Continuations 2015, held in London in April 2015, illustrate some of the afore mentioned topics and hopefully they will inspire further research work on the subject.