| 1. |
- Murray, Lawrence, et al.
(författare)
-
Delayed sampling and automatic Rao-Blackwellization of probabilistic programs
- 2018
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Ingår i: Proceedings of the 21st International Conference on Artificial Intelligence and Statistics (AISTATS), Lanzarote, Spain, April, 2018. - : PMLR.
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Konferensbidrag (refereegranskat)abstract
- We introduce a dynamic mechanism for the solution of analytically-tractable substructure in probabilistic programs, using conjugate priors and affine transformations to reduce variance in Monte Carlo estimators. For inference with Sequential Monte Carlo, this automatically yields improvements such as locallyoptimal proposals and Rao–Blackwellization. The mechanism maintains a directed graph alongside the running program that evolves dynamically as operations are triggered upon it. Nodes of the graph represent random variables, edges the analytically-tractable relationships between them. Random variables remain in the graph for as long as possible, to be sampled only when they are used by the program in a way that cannot be resolved analytically. In the meantime, they are conditioned on as many observations as possible. We demonstrate the mechanism with a few pedagogical examples, as well as a linearnonlinear state-space model with simulated data, and an epidemiological model with real data of a dengue outbreak in Micronesia. In all cases one or more variables are automatically marginalized out to significantly reduce variance in estimates of the marginal likelihood, in the final case facilitating a randomweight or pseudo-marginal-type importance sampler for parameter estimation. We have implemented the approach in Anglican and a new probabilistic programming language called Birch.
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| 2. |
- Abdalmoaty, Mohamed R. H., 1986-, et al.
(författare)
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Identification of Non-Linear Differential-Algebraic Equation Models with Process Disturbances
- 2021
-
Ingår i: 2021 60th IEEE Conference on Decision and Control (CDC). - : IEEE. - 9781665436595 - 9781665436588 - 9781665436601 ; , s. 2300-2305
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Konferensbidrag (refereegranskat)abstract
- Differential-algebraic equations (DAEs) arise naturally as a result of equation-based object-oriented modeling. In many cases, these models contain unknown parameters that have to be estimated using experimental data. However, often the system is subject to unknown disturbances which, if not taken into account in the estimation, can severely affect the model's accuracy. For non-linear state-space models, particle filter methods have been developed to tackle this issue. Unfortunately, applying such methods to non-linear DAEs requires a transformation into a state-space form, which is particularly difficult to obtain for models with process disturbances. In this paper, we propose a simulation-based prediction error method that can be used for non-linear DAEs where disturbances are modeled as continuous-time stochastic processes. To the authors' best knowledge, there are no general methods successfully dealing with parameter estimation for this type of model. One of the challenges in particle filtering methods are random variations in the minimized cost function due to the nature of the algorithm. In our approach, a similar phenomenon occurs and we explicitly consider how to sample the underlying continuous process to mitigate this problem. The method is illustrated numerically on a pendulum example. The results suggest that the method is able to deliver consistent estimates.
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| 3. |
- Aronsson, Peter, et al.
(författare)
-
Extendable Physical Unit Checking with Understandable Error Reporting
- 2009
-
Ingår i: Proceedings of the 7th International Modelica Conference. - Linköping : Linköping University Electronic Press, Linköpings universitet. - 9789173935135 ; , s. 890-897
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Konferensbidrag (refereegranskat)abstract
- Dimensional analysis and physical unit checking are important tools for helping users to detect and correct mistakes in dynamic mathematical models. To make tools useful in a broad range of domains, it is important to also support other units than the SI standard. For instance, such units are common in biochemical or financial modeling. Furthermore, if two or more units turn out be in conflict after checking, it is vital that the reported unit information is given in an understandable format for the user, e.g., “N.m” should preferably be shown instead of “m2.kg.s-2”, even if they represent the same unit. Presently, there is no standardized solution to handle these problems for Modelica models. The contribution presented in this paper is twofold. Firstly, we propose an extension to the Modelica language that makes it possible for a library designer to define both new base units and derived units within Modelica models and packets. Today this information is implicitly defined in the specification. Secondly, we describe and analyze a solution to the problem of presenting units to users in a more convenient way, based on an algorithm using Mixed Integer Programming (MIP). Both solutions are implemented, tested, and illustrated with several examples.
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| 4. |
- Bereza-Jarocinski, Robert, et al.
(författare)
-
Stochastic Approximation for Identification of Non-Linear Differential-Algebraic Equations with Process Disturbances
- 2022
-
Ingår i: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665467612 - 9781665467605 - 9781665467629 ; , s. 6712-6717
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Konferensbidrag (refereegranskat)abstract
- Differential-algebraic equations, commonly used to model physical systems, are the basis for many equation-based object-oriented modeling languages. When systems described by such equations are influenced by unknown process disturbances, estimating unknown parameters from experimental data becomes difficult. This is because of problems with the existence of well-defined solutions and the computational tractability of estimators. In this paper, we propose a way to minimize a cost function-whose minimizer is a consistent estimator of the true parameters-using stochastic gradient descent. This approach scales significantly better with the number of unknown parameters than other currently available methods for the same type of problem. The performance of the method is demonstrated through a simulation study with three unknown parameters. The experiments show a significantly reduced variance of the estimator, compared to an output error method neglecting the influence of process disturbances, as well as an ability to reduce the estimation bias of parameters that the output error method particularly struggles with.
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| 5. |
- Broman, David, 1977-, et al.
(författare)
-
A comparison of two metacompilation approaches to implementing a complex domaispecific language
- 2012
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Ingår i: Proceedings of the 27th Annual ACM Symposium on Applied Computing (SAC). - New York, NY, USA : ACM. - 9781450308571 ; , s. 1919-1921
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Konferensbidrag (refereegranskat)abstract
- Operational semantics and attribute grammars are examples of formalisms that can be used for generating compilers. We are interested in finding similarities and differences in how these approaches are applied to complex languages, and for generating compilers of such maturity that they have users in industry.As a specific case, we present a comparative analysis of two compilers for Modelica, a language for physical modeling, and which contains numerous compilation challenges. The two compilers are OpenModelica, which is based on big-step operational semantics, and JModelica.org, which is based on reference attribute grammars.
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| 6. |
- Broman, David, 1977-
(författare)
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A vision of miking : Interactive programmatic modeling, sound language composition, and self-learning compilation
- 2019
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Ingår i: SLE 2019 - Proceedings of the 12th ACM SIGPLAN International Conference on Software Language Engineering, co-located with SPLASH 2019. - New York, NY, USA : Association for Computing Machinery, Inc. - 9781450369817 ; , s. 55-60
-
Konferensbidrag (refereegranskat)abstract
- This paper introduces a vision of Miking, a language framework for constructing efficient and sound language environments and compilers for domain-specific modeling languages. In particular, this language framework has three key objectives: (i) to automatically generate interactive programmatic modeling environments, (ii) to guarantee sound compositions of language fragments that enable both rapid and safe domain-specific language development, (iii) to include first-class support for self-learning compilation, targeting heterogeneous execution platforms. The initiative is motivated in the domain of mathematical modeling languages. Specifically, two different example domains are discussed: (i) modeling, simulation, and verification of cyber-physical systems, and (ii) domain-specific differentiable probabilistic programming. The paper describes the main objectives of the vision, as well as concrete research challenges and research directions.
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| 7. |
- Broman, David, 1977-, et al.
(författare)
-
Abstract Syntax Can Make the Definition of Modelica Less Abstract
- 2007
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Ingår i: Proceedings of the 1st International Workshop on Equation-Based Object-Oriented Languages and Tools, Berlin, Germany. - 9789175198224 ; , s. 111-126
-
Konferensbidrag (refereegranskat)abstract
- Modelica is an open standardized language used for modeling and simulation of complex physical systems. The language specification defines a formal concrete syntax, but the semantics is informally described using natural language. The latter makes the language hard to interpret, maintain and reason about, which affect both tool development and language evolution. Even if a completely formal semantics of the Modelica language can be seen as a natural goal, it is a well-known fact that defining understandable and concise formal semantics specifications for large and complex languages is a very hard problem. In this paper, we will discuss different aspects of formulating a Modelica specification; both in terms of what should be specified and how it can be done. Moreover, we will further argue that a “middle-way” strategy can make the specification both clearer and easier to reason about. A proposal is outlined, where the current informally specified semantics is complemented with several grammars, specifying intermediate representations of abstract syntax. We believe that this kind of evolutionary strategy is easier to gain acceptance for, and is more realistic in the short-term, than a revolutionary approach of using a fully formal semantics definition of the language.
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| 8. |
- Broman, David, 1977-, et al.
(författare)
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Design Considerations for Dimensional Inference and Unit Consistency Checking in Modelica
- 2008
-
Ingår i: Proceedings of the 6th International Modelica Conference. - Bielefeld, Germany : Modelica Association. ; , s. 3-12
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Konferensbidrag (refereegranskat)abstract
- The Modelica language supports syntax for declaring physical units of variables, but it does not yet exist any defined semantics for how dimensional and unit consistency checking should be carried out. In this paper we explore different approaches and new constructs for improved dimensional inference and unit consistency checking in Modelica; both from an end-user, library, and tool perspective. A proposal for how dimensional inference and unit checking can be carried out is outlined and a prototype implementation is developed and verified using several examples from the Modelica standard library.
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| 9. |
- Broman, David, 1977-, et al.
(författare)
-
Determining Over- and Under-Constrained Systems of Equations using Structural Constraint Delta
- 2006
-
Ingår i: Proceedings of the 5th International Conference on Generative Programming and Component Engineering. - New York, NY, USA : ACM. ; , s. 151-160
-
Konferensbidrag (refereegranskat)abstract
- Computer aided modeling and simulation of complex physical systems, using components from multiple application domains, such as electrical, mechanical, and hydraulic, have in recent years witnessed a significant growth of interest. In the last decade, equation-based object-oriented (EOO) modeling languages, (e.g. Modelica, gPROMS, and VHDL-AMS) based on acausal modeling using Differential Algebraic Equations (DAEs), have appeared. With such languages, it is possible to model physical systems at a high level of abstraction by using reusable components.A model in an EOO language needs to have the same number of equations as unknowns. A previously unsolved problem concerning this property is the efficient detection of over- or under-constrained models in the case of separately compiled models.This paper describes a novel technique to determine over- and under-constrained systems of equations in models, based on a concept called structural constraint delta. In many cases it is also possible to locate the source of the constraint-problem. Our approach makes use of static type checking and consists of a type inference algorithm. We have implemented it for a subset of the Modelica language, and successfully validated it on several examples.
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| 10. |
- Broman, David, 1977-, et al.
(författare)
-
Functional programmatic modeling in modelyze
- 2019
-
Ingår i: ACM International Conference Proceeding Series. - New York, NY, USA : Association for Computing Machinery. - 9781450377133
-
Konferensbidrag (refereegranskat)abstract
- Recent years are characterized by a growing digitalization of production environment and other areas of human's life. Complex cyber-physical systems play a very important role within this development. Hence, integrated model-based design of such systems has gained significant attention. Quite naturally, this leads to the necessity of modeling hybrid system - systems containing both continuous-time and event-based phenomena. Hybrid modeling languages based on equations, supporting both continuous-time and eventbased aspects (e.g. Modelica, SysML, VHDL-AMS, and Simulink/Simscape) enable high-level reuse and integrated modeling capabilities of both the physically surrounding system and software for embedded systems. Using such equation-based object-oriented (EOO) modeling languages, it has become feasible to model complex systems covering multiple application domains at a high level of abstraction through reusable model components. They thus offer considerable advantages for many application areas. EOOLT is a forum for researchers with interests in all aspects of equation-based modeling languages and their supporting tools, including design, implementation, open issues limiting their expressiveness or usefulness, as well as novel applications.
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| 11. |
- Broman, David, 1977-, et al.
(författare)
-
Gradually typed symbolic expressions
- 2017
-
Ingår i: PEPM 2018 - Proceedings of the ACM SIGPLAN Workshop on Partial Evaluation and Program Manipulation, Co-located with POPL 2018. - New York, NY, USA : Association for Computing Machinery (ACM). - 9781450355872 ; , s. 15-29
-
Konferensbidrag (refereegranskat)abstract
- Embedding a domain-specific language (DSL) in a general purpose host language is an efficient way to develop a new DSL. Various kinds of languages and paradigms can be used as host languages, including object-oriented, functional, statically typed, and dynamically typed variants, all having their pros and cons. For deep embedding, statically typed languages enable early checking and potentially good DSL error messages, instead of reporting runtime errors. Dynamically typed languages, on the other hand, enable flexible transformations, thus avoiding extensive boilerplate code. In this paper, we introduce the concept of gradually typed symbolic expressions that mix static and dynamic typing for symbolic data. The key idea is to combine the strengths of dynamic and static typing in the context of deep embedding of DSLs. We define a gradually typed calculus <*>, formalize its type system and dynamic semantics, and prove type safety. We introduce a host language called Modelyze that is based on <*>, and evaluate the approach by embedding a series of equation-based domain-specific modeling languages, all within the domain of physical modeling and simulation.
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| 12. |
- Broman, David, 1977-
(författare)
-
Growing an Equation-Based Object-Oriented Modeling Language
- 2009
-
Ingår i: Proceedings of the 6th Vienna International Conference on Mathematical Modelling (MATHMOD 2009 ). - 9783901608353 ; , s. 1316-1324
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Equation-based object-oriented (EOO) modeling languages are typically rather complex. Such languages can unfortunately not be designed correctly once and for all, not least because all requirements and use cases are not known initially, and may never be known completely. Hence, there is a need to plan for modeling languages to grow in a sound manner. This paper discusses and analyzes how EOO languages in general can be designed for growth, and in particular how this relates to the evolution of the Modelica language. Different ways of growth are categorized and various stakeholders’ perspectives are discussed regarding what is important when growing a language.
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| 13. |
- Broman, David, 1977-, et al.
(författare)
-
Higher-Order Acausal Models
- 2008
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Ingår i: EOOLT 2008. - : Linköping University Electronic Press. - 9789175198231 ; , s. 59-69
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Current equation-based object-oriented (EOO) languages typically contain a number of fairly complex language constructs for enabling reuse of models. However, support for model transformation is still often limited to scripting solutions provided by tool implementations. In this paper we investigate the possibility of combining the well known concept of higher-order functions, used in standard functional programming languages, with acausal models. This concept, called Higher-Order Acausal Models (HOAMs), simplifies the creation of reusable model libraries and model transformations within the modeling language itself. These transformations include general model composition and recursion operations and do not require data representation/reification of models as in metaprogramming/metamodeling. Examples within the electrical and mechanical domain are given using a small research language. However, the language concept is not limited to a particular language, and could in the future be incorporated into existing commercially available EOO-languages.
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| 14. |
- Broman, David, 1977-
(författare)
-
Hybrid Simulation Safety : Limbos and Zero Crossings
- 2018
-
Ingår i: Principles of Modeling. - Cham : Springer. - 9783319952451 ; , s. 106-121
-
Bokkapitel (refereegranskat)abstract
- Physical systems can be naturally modeled by combining continuous and discrete models. Such hybrid models may simplify the modeling task of complex system, as well as increase simulation performance. Moreover, modern simulation engines can often efficiently generate simulation traces, but how do we know that the simulation results are correct? If we detect an error, is the error in the model or in the simulation itself? This paper discusses the problem of simulation safety, with the focus on hybrid modeling and simulation. In particular, two key aspects are studied: safe zero-crossing detection and deterministic hybrid event handling. The problems and solutions are discussed and partially implemented in Modelica and Ptolemy II.
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| 15. |
- Broman, David, 1977-, et al.
(författare)
-
Ideas for Security Assurance in Security Critical Software using Modelica
- 2005
-
Konferensbidrag (refereegranskat)abstract
- Due to the increasing number of vulnerabilities in software systems and customers- need to trust the producers- development process, third party security evaluations, such as Common Criteria (CC), are today commonly used to provide assurance of security critical software. Modelica is a modern, strongly typed, declarative, and object-oriented language for modeling and simulation of complex systems. In this paper we sketch two ideas for improving security assurance, by expanding the scope of Modelica into also becoming a declarative modeling language for other application areas than simulation.
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| 16. |
- Broman, David, 1977-
(författare)
-
Interactive Programmatic Modeling
- 2021
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Ingår i: ACM Transactions on Embedded Computing Systems. - : ACM Digital Library. - 1539-9087 .- 1558-3465. ; 20:4, s. 1-26
-
Tidskriftsartikel (refereegranskat)abstract
- Modeling and computational analyses are fundamental activities within science and engineering. Analysis activities can take various forms, such as simulation of executable models, formal verification of model properties, or inference of hidden model variables. Traditionally, tools for modeling and analysis have similar workflows: (i) a user designs a textual or graphical model or the model is inferred from data, (ii) a tool performs computational analyses on the model, and (iii) a visualization tool displays the resulting data. This article identifies three inherent problems with the traditional approach: the recomputation problem, the variable inspection problem, and the model expressiveness problem. As a solution, we propose a conceptual framework called Interactive Programmatic Modeling. We formalize the interface of the framework and illustrate how it can be used in two different domains: equation-based modeling and probabilistic programming.
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| 17. |
- Broman, David, 1977-
(författare)
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Meta-Languages and Semantics for Equation-Based Modeling and Simulation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Performing computational experiments on mathematical models instead of building and testing physical prototypes can drastically reduce the develop cost for complex systems such as automobiles, aircraft, and powerplants. In the past three decades, a new category of equation-based modeling languages has appeared that is based on acausal and object-oriented modeling principles, enabling good reuse of models. However, the modeling languages within this category have grown to be large and complex, where the specifications of the language's semantics are informally defined, typically described in natural languages. The lack of a formal semantics makes these languages hard to interpret unambiguously and to reason about. This thesis concerns the problem of designing the semantics of such equation-based modeling languages in a way that allows formal reasoning and increased correctness. The work is presented in two parts.In the first part we study the state-of-the-art modeling language Modelica. We analyze the concepts of types in Modelica and conclude that there are two kinds of type concepts: class types and object types. Moreover, a concept called structural constraint delta is proposed, which is used for isolating the faults of an over- or under-determined model.In the second part, we introduce a new research language called the Modeling Kernel Language (MKL). By introducing the concept of higher-order acausal models (HOAMs), we show that it is possible to create expressive modeling libraries in a manner analogous to Modelica, but using a small and simple language concept. In contrast to the current state-of-the-art modeling languages, the semantics of how to use the models, including meta operations on models, are also specified in MKL libraries. This enables extensible formal executable specifications where important language features are expressed through libraries rather than by adding completely new language constructs. MKL is a statically typed language based on a typed lambda calculus. We define the core of the language formally using operational semantics and prove type safety. An MKL interpreter is implemented and verified in comparison with a Modelica environment.
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| 18. |
- Broman, David, 1977-, et al.
(författare)
-
Node-Based Connection Semanticsfor Equation-Based Object-Oriented Modeling Languages
- 2012
-
Ingår i: <em>Proceedings of Fourteenth International Symposium on Practical Aspects of Declarative Languages (PADL 2012)</em>. - Berlin, Heidelberg : Springer Berlin Heidelberg. ; , s. 258-272
-
Konferensbidrag (refereegranskat)abstract
- Declarative, Equation-Based Object-Oriented (EOO) modeling languages, like Modelica, support modeling of physical systems by composition of reusable component models. An important application area is modeling of cyber-physical systems. EOO languages typically feature a connection construct allowing component models to be assembled into systems much like physical components are. Different designs are possible. This paper introduces, formalizes, and validates an approach based on explicit nodes that expressly is designed to work for functional EOO languages supporting higher-order modeling. The paper also considers Modelica-style connections and explains why that design does not work for functional EOO languages, thus mapping out the design space.
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| 19. |
- Broman, David, 1977-, et al.
(författare)
-
Requirements for Hybrid Cosimulation Standards
- 2015
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Ingår i: Proceedings of 18th ACM International Conference on Hybrid Systems: Computation and Control (HSCC). - New York, NY, USA : ACM Digital Library. - 9781450334334 ; , s. 179-188
-
Konferensbidrag (refereegranskat)abstract
- This paper defines a suite of requirements for future hybrid cosimulation standards, and specifically provides guidance for development of a hybrid cosimulation version of the Functional Mockup Interface (FMI). A cosimulation standard defines interfaces that enable diverse simulation tools to interoperate. Specifically, one tool defines a component that forms part of a simulation model in another tool. We focus on components with inputs and outputs that are functions of time, and specifically on mixtures of discrete events and continuous time signals. This hybrid mixture is not well supported by existing cosimulation standards, and specifically not by FMI 2.0, for reasons that are explained in this paper. The paper defines a suite of test components, giving a mathematical model of an ideal behavior, plus a discussion of practical implementation considerations. The discussion includes acceptance criteria by which we can determine whether a standard supports definition of each component. In addition, we define a set of test compositions that define requirements for coordination between components, including consistent handling of timed events.
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| 20. |
- Broman, David, 1977-
(författare)
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Safety, Security, and Semantic Aspects of Equation-Based Object-Oriented Languages and Environments
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last two decades, the interest for computer aided modeling and simulation of complex physical systems has witnessed a significant growth. The recent possibility to create acausal models, using components from different domains (e.g., electrical, mechanical, and hydraulic) enables new opportunities. Modelica is one of the most prominent equation-based object-oriented (EOO) languages that support such capabilities, including the ability to simulate both continuous- and discrete-time models, as well as mixed hybrid models. However, there are still many remaining challenges when it comes to language safety and simulation security. The problem area concerns detecting modeling errors at an early stage, so that faults can be isolated and resolved. Furthermore, to give guarantees for the absence of faults in models, the need for precise language specifications is vital, both regarding type systems and dynamic semantics.This thesis includes five papers related to these topics. The first paper describes the informal concept of types in the Modelica language, and proposes a new concrete syntax for more precise type definitions. The second paper provides a new approach for detecting over- and under-constrained systems of equations in EOO languages, based on a concept called structural constraint delta. That approach makes use of type checking and a type inference algorithm. The third paper outlines a strategy for using abstract syntax as a middle-way between a formal and informal language specification. The fourth paper suggests and evaluates an approach for secure distributed co-simulation over wide area networks. The final paper outlines a new formal operational semantics for describing physical connections, which is based on the untyped lambda calculus. A kernel language is defined, in which real physical models are constructed and simulated.
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| 21. |
- Broman, David, 1977-
(författare)
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Should Software Engineering Projects be the Backbone or the Tail of Computing Curricula?
- 2010
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Ingår i: Software Engineering Education and Training (CSEE&T), 2010. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781424470525 ; , s. 153-156
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Konferensbidrag (refereegranskat)abstract
- Most computer science (CS) and software engineering (SE) curricula include some form of SE project with the aim of lowering the gap between CS and SE education and real-world demands in industry. In this paper we briefly discuss and explain our findings of software engineering projects taught at LiU in Sweden. These courses use what we call the ¿tail¿ approach, where student projects are performed at the end of a degree program. We then argue that there are several problems with this approach and sketch an idea where SE projects are an integrated part of a curriculum. Furthermore, pros and cons of this idea, which we call the SE project ¿backbone¿ approach, are discussed and analyzed.
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| 22. |
- Broman, David, 1977-, et al.
(författare)
-
The Company Approach to Software Engineering Project Courses
- 2012
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Ingår i: IEEE Transactions on Education. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9359 .- 1557-9638. ; 55:4, s. 445-452
-
Tidskriftsartikel (refereegranskat)abstract
- Teaching larger software engineering project courses at the end of a computing curriculum is a way for students to learn some aspects of real-world jobs in industry. Such courses, often referred to as capstone courses, are effective for learning how to apply the skills they have acquired in, for example, design, test, and configuration management. However, these courses are typically performed in small teams, giving only a limited realistic perspective of problems faced when working in real companies. This paper describes an alternative approach to classic capstone projects, with the aim of being more realistic from an organizational, process, and communication perspective. This methodology, called the company approach, is described by intended learning outcomes, teaching/learning activities, and assessment tasks. The approach is implemented and evaluated in a larger Masters student course.
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| 23. |
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| 24. |
- Broman, David, 1977-, et al.
(författare)
-
Types in the Modelica Language
- 2006
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Ingår i: Proceedings of the Fifth International Modelica Conference. ; , s. 303-315
-
Konferensbidrag (refereegranskat)abstract
- Modelica is an object-oriented language designed for modeling and simulation of complex physical systems. To enable the possibility for an engineer to discover errors in a model, languages and compilers are making use of the concept of types and type checking. This paper gives an overview of the concept of types in the context of the Modelica language. Furthermore, a new concrete syntax for describing Modelica types is given as a starting point to formalize types in Modelica. Finally, it is concluded that the current state of the Modelica language specification is too informal and should in the long term be augmented by a formal definition.
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| 25. |
- Cremona, F., et al.
(författare)
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Hybrid Co-simulation : It's about time
- 2018
-
Ingår i: Proceedings - 21st ACM/IEEE International Conference on Model Driven Engineering Languages and Systems, MODELS 2018. - New York, NY, USA : Association for Computing Machinery, Inc. - 9781450349499
-
Konferensbidrag (refereegranskat)abstract
- Model-based design methodologies are commonly used in industry for the development of cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting the weaknesses of a particular tool, an alternative is to embrace heterogeneity and develop tool integration platforms and protocols to leverage the strengths from other environments. A fairly recent attempt in this direction is an open interface standard called Functional Mock-up Interface (FMI), which is focused on the convenient exchange and co-simulation of simulation models (Functional Mock-up Units, FMUs), primarily between component suppliers and OEMs. As it stands, FMI has reached acceptance in industry, but its specification (version 2.0) provides only limited support for hybrid co-simulation-simulating systems that mix continuous and discrete behaviors, which are commonly used to model CPSs. This paper identifies FMI's time representation based on floating-point numbers as a key problem, because it does not support well the discrete events that typically occur at the cyber-physical boundary; it is only suitable for modeling continuous dynamics without discrete behaviors. While time is a central concept in reasoning about the physical world, it is largely abstracted away when reasoning about the cyber world. As a result, the engineering methods for CPSs have misaligned abstractions between the physics domain, the mathematical domain used to model physics, the computational domain used to implement these mathematical abstractions for simulation, and the computational domain used on the cyber side of CPSs. The most common resolution for this conundrum is to adopt the naive Newtonian ideal model of time, where time is a real number known everywhere and advancing uniformly. But ironically, Newtonian time proves not so practical for hybrid co-simulation. The obvious reason is that digital computers do not work with real numbers. Whereas real numbers have infinite precision, their floating-point representation does not. This discrepancy leads to unpredictable quantization errors that may accumulate. Although real numbers can be compared for equality (e.g., to define “simultaneity”), it rarely makes sense to do so for floating-point numbers. We show that the approach taken in FMI (and many other modeling frameworks) that embraces a naive Newtonian physical model of time, and a cyber-approximation of this model using floating-point numbers, is inadequate for CPSs; it leads to models with unnecessarily inexplicable, nondeterministic, and complex behaviors. Our analysis concludes that a model of time that solely uses integers solves many of these problems. Specifically, we propose to use a 64-bit unsigned integer representation with arbitrary resolution, given as a power of ten, allowing model parameters specified in decimal to be represented exactly (granted ample resolution). Integer arithmetic is computationally efficient, and, for well-chosen resolutions, this representation will tolerate very long simulations without overflow. It is also easily converted to and from floating-point representations, albeit not losslessly. Given the vast range of time scales used across different simulation models, we believe that choosing a fixed universal time resolution does not make sense. Instead, we describe an algorithm that picks an adequate time resolution for a particular model and we provide procedures for time quantization needed to reconcile discrepacies between internal time representations of co-simulated FMUs. We propose concrete extensions to the FMI standard for the support of hybrid co-simulation that enable the use of integer time, automatic choice of time resolution, and the use of absent signals. We explain in detail how these extensions can be implemented mod-ularly within the frameworks of existing simulation environments and with support for legacy FMUs and superdense time.
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| 26. |
- Cremona, Fabio, et al.
(författare)
-
Hybrid co-simulation : it's about time
- 2019
-
Ingår i: Software and Systems Modeling. - : Springer Nature. - 1619-1366 .- 1619-1374. ; 18:3, s. 1655-1679
-
Tidskriftsartikel (refereegranskat)abstract
- Model-based design methodologies are commonly used in industry for the development of complex cyber-physical systems (CPSs). There are many different languages, tools, and formalisms for model-based design, each with its strengths and weaknesses. Instead of accepting some weaknesses of a particular tool, an alternative is to embrace heterogeneity, and to develop tool integration platforms and protocols to leverage the strengths from different environments. A fairly recent attempt in this direction is the functional mock-up interface (FMI) standard that includes support for co-simulation. Although this standard has reached acceptance in industry, it provides only limited support for simulating systems that mix continuous and discrete behavior, which are typical of CPS. This paper identifies the representation of time as a key problem, because the FMI representation does not support well the discrete events that typically occur at the cyber-physical boundary. We analyze alternatives for representing time in hybrid co-simulation and conclude that a superdense model of time using integers only solves many of these problems. We show how an execution engine can pick an adequate time resolution, and how disparities between time representations internal to co-simulated components and the resulting effects of time quantization can be managed. We propose a concrete extension to the FMI standard for supporting hybrid co-simulation that includes integer time, automatic choice of time resolution, and the use of absent signals. We explain how these extensions can be implemented modularly within the frameworks of existing simulation environments.
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| 27. |
- Cremona, Fabio, et al.
(författare)
-
Step Revision in Hybrid Co-simulation with FMI
- 2016
-
Ingår i: Proceedings of the 14th ACM-IEEE International Conference on formal Methods and Models for System Design (MEMOCODE). - : IEEE conference proceedings. - 9781509027910
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a master algorithm for co-simulation of hybrid systems using the Functional Mock-up Interface (FMI) standard. Our algorithm introduces step revision to achieve an accurate and precise handling of mixtures of continuous-time and discrete-event signals, particularly in the situation where components are unable to accurately extrapolate their input. Step revision provides an efficient means to respect the error bounds of numerical approximation algorithms that operate inside co-simulated FMUs. We first explain the most fundamental issues associated with hybrid co-simulation and analyze them in the framework of FMI. We demonstrate the necessity for step revision to address some of these issues and formally describe a master algorithm that supports it. Finally, we present experimental results obtained through our reference implementation that is part of our publicly available open-source toolchain called FIDE.
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| 28. |
- Desai, Ankush, et al.
(författare)
-
Approximate synchrony: An abstraction for distributed almost-synchronous systems
- 2015
-
Ingår i: Proceedings of the 27th International Conference on Computer Aided Verification, CAV 2015. - Cham : Springer. - 9783319216676 ; , s. 429-448
-
Konferensbidrag (refereegranskat)abstract
- Forms of synchrony can greatly simplify modeling, design, and verification of distributed systems. Thus, recent advances in clock synchronization protocols and their adoption hold promise for system design. However, these protocols synchronize the distributed clocks only within a certain tolerance, and there are transient phases while synchronization is still being achieved. Abstractions used for modeling and verification of such systems should accurately capture these imperfections that cause the system to only be “almost synchronized.” In this paper, we present approximate synchrony, a sound and tunable abstraction for verification of almost-synchronous systems. We show how approximate synchrony can be used for verification of both time synchronization protocols and applications running on top of them. We provide an algorithmic approach for constructing this abstraction for symmetric, almost-synchronous systems, a subclass of almost-synchronous systems. Moreover, we show how approximate synchrony also provides a useful strategy to guide state-space exploration. We have implemented approximate synchrony as a part of a model checker and used it to verify models of the Best Master Clock (BMC) algorithm, the core component of the IEEE 1588 precision time protocol, as well as the time-synchronized channel hopping protocol that is part of the IEEE 802.15.4e standard.
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| 29. |
- Eriksson, Oscar, et al.
(författare)
-
Partial Evaluation of Automatic Differentiation for Differential-Algebraic Equations Solvers
- 2023
-
Ingår i: GPCE 2023 - Proceedings of the 22nd ACM SIGPLAN International Conference on Generative Programming: Concepts and Experiences, Co-located with: SPLASH 2023. - : Association for Computing Machinery (ACM). ; , s. 57-71
-
Konferensbidrag (refereegranskat)abstract
- Differential-Algebraic Equations (DAEs) are the foundation of high-level equation-based languages for modeling physical dynamical systems. Simulating models in such languages requires a transformation known as index reduction that involves differentiating individual equations before numerical integration. Commercial and open-source implementations typically perform index reduction by symbolic differentiation (SD) and produce a Jacobian callback function with forward-mode automatic differentiation (AD). The former results in efficient runtime code, and the latter is asymptotically efficient in both runtime and code size. However, AD introduces runtime overhead caused by a non-standard representation of real numbers, and SD is not always applicable in models with general recursion. This work proposes a new approach that uses partial evaluation of AD in the context of numerical DAE solving to combine the strengths of the two differentiation methods while mitigating their weaknesses. Moreover, our approach selectively specializes partial derivatives of the Jacobian by exploiting structural knowledge while respecting a user-defined bound on the code size. Our evaluation shows that the new method both enables expressive modeling from AD and retains the efficiency of SD for many practical applications.
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| 30. |
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| 31. |
- Fritzson, Peter, et al.
(författare)
-
Equation-based object-oriented languages and tool : Report on the Workshop EOOLT 2007 at ECOOP 2007
- 2007
-
Ingår i: Object-Oriented Technology. - Berlin, Heidelberg : Springer. - 9783540781943 - 9783540781950 ; , s. 27-39
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- EOOLT'2007 was the first edition of the ECOOP-EOOLT workshop. ne workshop is intended to bring researchers associated with different equation-based object-oriented (EOO) modeling languages and different application areas making use of such languages together. The aim of the workshop is to explore common grounds and derive software design principles that may make future EOO modeling languages more robust, more versatile, and more widely accepted among the various stakeholders. At EOOLT'2007, nineteen researchers with diverse backgrounds and needs came together to present and discuss fourteen different concept papers grouped into the four topic areas of integrated system modeling approaches; hybrid modeling and variable structure systems; modeling languages, specification, and language comparison; and tools and methods.
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| 32. |
- Fritzson, Peter, et al.
(författare)
-
Equation-based object-oriented modeling languages and tools : Report on the workshop EOOLT 2010 at MODELS 2010 Oslo, Norway, October 3, 2010
- 2011
-
Ingår i: Models in Software Engineering. - Berlin, Heidelberg : Springer. - 9783642212093 - 9783642212109 ; , s. 140-144
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- EOOLT 2010 was the third edition of the EOOLT workshop series. The workshop is intended to bring together researchers and practitioners fromdifferent equation-based object-oriented (EOO) modeling language communities. This year’s workshop also expands the scope to include the whole design space of languages for cyber-physical systems, where physical dynamics are mixed with networks and software. The workshop gathered 31 participants to present and discuss thirteen different papers grouped into the four areas of real-time oriented modeling languages and tools, modeling language design, simulation and model compilation, and modeling and simulation tools.
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| 33. |
- Fritzson, Peter, et al.
(författare)
-
Formal Semantics Based Translator Generation and Tool Development in Practice
- 2009
-
Ingår i: Proceedings of 20th Australian Software Engineering Conference (ASWEC 2009). - : IEEE Computer Society. - 9780769535999 ; , s. 256-266
-
Konferensbidrag (refereegranskat)abstract
- In this paper we report on a long-term research effort to develop and use efficient language implementation generators in practice. The generator is applied to a number of different languages, some of which are used for projects in industry. The used formal specification style is operational semantics, primarily in the form called natural semantics, represented and supported by a meta-language and tool called the relational meta language (RML), which can generate efficient implementations in C, on par with hand-implemented code. Generating implementations from formal specifications are assumed to give advantages such as: high level descriptions, higher degree of correctness, and consistency between specification and implementation. To what extent can this be realized in practice? Does it scale to large language implementations? To answer some of these questions we have developed specifications of a range of languages: imperative, functional, object-oriented (Java), and equation-based (Modelica). The size of specifications range from half a page to large specifications of 60 000 lines. It turns out to be possible to generate efficient compilers, also for large languages. However, the performance of the generator tool and the user support of the development environment become increasingly important for large specifications. To satisfy such user needs the speed of the generator was increased a factor of ten to reduce turn-around time, and an Eclipse plug-in including a debugger were developed. For very large specifications, the structuring and modularity of the specification itself also become essential for performance and maintainability.
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| 34. |
- Fritzson, Peter, 1952-, et al.
(författare)
-
OpenModelica - A Free Open-Source Environment for System Modeling, Simulation, and Teaching
- 2006
-
Ingår i: Proceedings of the2006 IEEE International Conference on Control Applications (CCA)2006 IEEE Conference on Computer-Aided Control Systems Design (CACSD)2006 IEEE International Symposium on Intelligent Control (ISIC). - Munich, Germany : IEEE. - 0780397975 - 0780397975 ; , s. 1588-1595
-
Konferensbidrag (refereegranskat)abstract
- Modelica is a modern, strongly typed, declarative, and object-oriented language for modeling and simulation of complex systems. This paper gives a quick overview of some aspects of the OpenModelica environment - an open-source environment for modeling, simulation, and development of Modelica applications. An introduction of the objectives of the environment is given, an overview of the architecture is outlined and a number of examples are illustrated.
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| 35. |
- Fuhrmann, Insa, et al.
(författare)
-
Time for Reactive System Modeling : Interactive Timing Analysis with Hotspot Highlighting
- 2016
-
Ingår i: In Proceedings of the 24th International Conference on Real-Time Networks and Systems (RTNS 2016). - New York, NY, USA : ACM Press. - 9781450347877
-
Konferensbidrag (refereegranskat)abstract
- Modeling tools typically provide no information about timing properties and costly parts of the system under development. In this paper we propose a generic approach to integrate timing analysis and modeling tools. This approach includes visual highlighting to guide the user to worst-case execution time hotspots, detailed timing information for specific model elements, and the separation of di↵erent types of timing val- ues. Our solution includes both a way to keep track of model elements subject to timing analysis during the compilation process, and a flexible and formally defined timing analysis interface for communicating timing information between a high-level modeling tool and a lower-level timing analysis tool. We present a complete open-source, Eclipse-based pro- totype tool chain that is evaluated both using a systematic benchmark suite and a user study.
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| 36. |
- Gomes, Claudio, et al.
(författare)
-
Co-Simulation : A Survey
- 2018
-
Ingår i: ACM Computing Surveys. - : Association for Computing Machinery (ACM). - 0360-0300 .- 1557-7341. ; 51:3
-
Tidskriftsartikel (refereegranskat)abstract
- Modeling and simulation techniques are today extensively used both in industry and science. Parts of larger systems are, however, typically modeled and simulated by different techniques, tools, and algorithms. In addition, experts from different disciplines use various modeling and simulation techniques. Both these facts make it difficult to study coupled heterogeneous systems. Co-simulation is an emerging enabling technique, where global simulation of a coupled system can be achieved by composing the simulations of its parts. Due to its potential and interdisciplinary nature, cosimulation is being studied in different disciplines but with limited sharing of findings. In this survey, we study and survey the state-of-the-art techniques for co-simulation, with the goal of enhancing future research and highlighting the main challenges. To study this broad topic, we start by focusing on discrete-event-based co-simulation, followed by continuous-time-based co-simulation. Finally, we explore the interactions between these two paradigms, in hybrid co-simulation. To survey the current techniques, tools, and research challenges, we systematically classify recently published research literature on co-simulation, and summarize it into a taxonomy. As a result, we identify the need for finding generic approaches for modular, stable, and accurate coupling of simulation units, as well as expressing the adaptations required to ensure that the coupling is correct.
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| 37. |
- Gross, James, Professor, 1975-, et al.
(författare)
-
TECoSA – Trends, Drivers, and Strategic Directions for Trustworthy Edge Computing in Industrial Applications
- 2022
-
Ingår i: INSIGHT. - : Wiley. - 2156-485X .- 2156-4868. ; 25:4, s. 29-34
-
Tidskriftsartikel (refereegranskat)abstract
- TECoSA – a university-based research center in collaboration with industry – was established early in 2020, focusing on Trustworthy Edge Computing Systems and Applications. This article summarizes and assesses the current trends and drivers regarding edge computing. In our analysis, edge computing provided by mobile network operators will be the initial dominating form of this new computing paradigm for the coming decade. These insights form the basis for the research agenda of the TECoSA center, highlighting more advanced use cases, including AR/VR/Cognitive Assistance, cyber-physical systems, and distributed machine learning. The article further elaborates on the identified strategic directions given these trends, emphasizing testbeds and collaborative multidisciplinary research.
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| 38. |
- Harrand, Nicolas, et al.
(författare)
-
Automatic Diversity in the Software Supply Chain
- 2021
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Despite its obvious benefits, the increased adoption of package managers to automate the reuse of libraries has opened the door to a new class of hazards: supply chain attacks. By injecting malicious code in one library, an attacker may compromise all instances of all applications that depend on the library. To mitigate the impact of supply chain attacks, we propose the concept of Library Substitution Framework. This novel concept leverages one key observation: when an application depends on a library, it is very likely that there exists other libraries that provide similar features. The key objective of Library Substitution Framework is to enable the developers of an application to harness this diversity of libraries in their supply chain. The framework lets them generate a population of application variants, each depending on a different alternative library that provides similar functionalities. To investigate the relevance of this concept, we develop ARGO, a proof-of-concept implementation of this framework that harnesses the diversity of JSON suppliers. We study the feasibility of library substitution and its impact on a set of 368 clients. Our empirical results show that for 195 of the 368 java applications tested, we can substitute the original JSON library used by the client by at least 15 other JSON libraries without modifying the client's code. These results show the capacity of a Library Substitution Framework to diversify the supply chain of the client applications of the libraries it targets.
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| 39. |
- Harrand, Nicolas, 1991-
(författare)
-
Software Diversity for Third-Party Dependencies
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thanks to the emergence of package managers and online software repositories, modern software development heavily relies on the reuse of third-party libraries. This practice has significant benefits in terms of productivity and reliability. Yet, the reuse of software libraries leads large groups of applications to share a significant amount of code, including potential defects such as bugs or vulnerabilities. The lack of diversity in these group of applications make them more prone to large-scale failures, and more predictable for attackers attempting to exploit their shared vulnerabilities.To mitigate these risks opened by library reuse, this dissertation proposes to introduce diversity in software applications.We create variants of software applications through transformations targeting the libraries they depend on. These variants provide functionalities equivalent to their original, while not sharing the exact same behavior.In this dissertation, we cover three aspects of software diversity.First, we study the existing behavioral diversity of alternative libraries implementing similar functionalities.We perform two case studies on two families of reusable software artifacts: JSON libraries and Bytecode decompilers. We provide empirical evidence that both groups of artifacts exhibit significant natural input/output behavioral diversity.Second, we study software transformations targeting libraries themselves. We propose six source-to-source transformations targeting software libraries, as well as a general architecture to implement library substitution. We implement this architecture in a JSON library substitution framework, leveraging the diversity of behavior we observe in JSON libraries. We assess the impact of these transformations on open-source libraries and software applications through two experiments.Finally, we study the properties of software applications and libraries that make them prone to transformation without changing their functionalities. We analyze the variants produced during our software diversification experiments and discuss our findings. In particular, we observe that the existence of alternative implementations at different granularity, instructions, methods, classes, and libraries, provides an important source of potential diversity that can be leveraged.
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| 40. |
- Harrand, Nicolas, et al.
(författare)
-
The Behavioral Diversity of Java JSON Libraries
- 2021
-
Ingår i: 2021 IEEE 32nd International Symposium on Software Reliability Engineering (ISSRE). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- JSON is an essential file and data format in domains that span scientific computing, web APIs or configuration management. Its popularity has motivated significant software development effort to build multiple libraries to process JSON data. Previous studies focus on performance comparison among these libraries and lack a software engineering perspective. We present the first systematic analysis and comparison of the input / output behavior of 20 JSON libraries, in a single software ecosystem: Java/Maven. We assess behavior diversity by running each library against a curated set of 473 JSON files, including both well-formed and ill-formed files. The main design differences, which influence the behavior of the libraries, relate to the choice of data structure to represent JSON objects and to the encoding of numbers. We observe a remarkable behavioral diversity with ill-formed files, or corner cases such as large numbers or duplicate data. Our unique behavioral assessment of JSON libraries paves the way for a robust processing of ill-formed files, through a multi-version architecture.
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| 41. |
- Isaac, Liu, et al.
(författare)
-
A PRET microarchitecture implementation with repeatable timing and competitive performance
- 2012
-
Ingår i: Proceedings of the 30th IEEE International Conference on Computer Design (ICCD 2012). - : IEEE conference proceedings. - 9781467330510 ; , s. 87-93
-
Konferensbidrag (refereegranskat)abstract
- We contend that repeatability of execution times is crucial to the validity of testing of real-time systems. However, computer architecture designs fail to deliver repeatable timing, a consequence of aggressive techniques that improve average-case performance. This paper introduces the Precision-Timed ARM (PTARM), a precision-timed (PRET) microarchitecture implementation that exhibits repeatable execution times without sacrificing performance. The PTARM employs a repeatable thread-interleaved pipeline with an exposed memory hierarchy, including a repeatable DRAM controller. Our benchmarks show an improved throughput compared to a single-threaded in-order five-stage pipeline, given sufficient parallelism in the software.
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| 42. |
- Jonsson, Leif, et al.
(författare)
-
Automatic Localization of Bugs to Faulty Components in Large Scale Software Systems using Bayesian Classification
- 2016
-
Ingår i: 2016 IEEE INTERNATIONAL CONFERENCE ON SOFTWARE QUALITY, RELIABILITY AND SECURITY (QRS 2016). - : IEEE. - 9781509041275 ; , s. 425-432
-
Konferensbidrag (refereegranskat)abstract
- We suggest a Bayesian approach to the problem of reducing bug turnaround time in large software development organizations. Our approach is to use classification to predict where bugs are located in components. This classification is a form of automatic fault localization (AFL) at the component level. The approach only relies on historical bug reports and does not require detailed analysis of source code or detailed test runs. Our approach addresses two problems identified in user studies of AFL tools. The first problem concerns the trust in which the user can put in the results of the tool. The second problem concerns understanding how the results were computed. The proposed model quantifies the uncertainty in its predictions and all estimated model parameters. Additionally, the output of the model explains why a result was suggested. We evaluate the approach on more than 50000 bugs.
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| 43. |
- Jonsson, Leif, 1973-
(författare)
-
Machine Learning-Based Bug Handling in Large-Scale Software Development
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the possibilities of automating parts of the bug handling process in large-scale software development organizations. The bug handling process is a large part of the mostly manual, and very costly, maintenance of software systems. Automating parts of this time consuming and very laborious process could save large amounts of time and effort wasted on dealing with bug reports. In this thesis we focus on two aspects of the bug handling process, bug assignment and fault localization. Bug assignment is the process of assigning a newly registered bug report to a design team or developer. Fault localization is the process of finding where in a software architecture the fault causing the bug report should be solved. The main reason these tasks are not automated is that they are considered hard to automate, requiring human expertise and creativity. This thesis examines the possi- bility of using machine learning techniques for automating at least parts of these processes. We call these automated techniques Automated Bug Assignment (ABA) and Automatic Fault Localization (AFL), respectively. We treat both of these problems as classification problems. In ABA, the classes are the design teams in the development organization. In AFL, the classes consist of the software components in the software architecture. We focus on a high level fault localization that it is suitable to integrate into the initial support flow of large software development organizations.The thesis consists of six papers that investigate different aspects of the AFL and ABA problems. The first two papers are empirical and exploratory in nature, examining the ABA problem using existing machine learning techniques but introducing ensembles into the ABA context. In the first paper we show that, like in many other contexts, ensembles such as the stacked generalizer (or stacking) improves classification accuracy compared to individual classifiers when evaluated using cross fold validation. The second paper thor- oughly explore many aspects such as training set size, age of bug reports and different types of evaluation of the ABA problem in the context of stacking. The second paper also expands upon the first paper in that the number of industry bug reports, roughly 50,000, from two large-scale industry software development contexts. It is still as far as we are aware, the largest study on real industry data on this topic to this date. The third and sixth papers, are theoretical, improving inference in a now classic machine learning tech- nique for topic modeling called Latent Dirichlet Allocation (LDA). We show that, unlike the currently dominating approximate approaches, we can do parallel inference in the LDA model with a mathematically correct algorithm, without sacrificing efficiency or speed. The approaches are evaluated on standard research datasets, measuring various aspects such as sampling efficiency and execution time. Paper four, also theoretical, then builds upon the LDA model and introduces a novel supervised Bayesian classification model that we call DOLDA. The DOLDA model deals with both textual content and, structured numeric, and nominal inputs in the same model. The approach is evaluated on a new data set extracted from IMDb which have the structure of containing both nominal and textual data. The model is evaluated using two approaches. First, by accuracy, using cross fold validation. Second, by comparing the simplicity of the final model with that of other approaches. In paper five we empirically study the performance, in terms of prediction accuracy, of the DOLDA model applied to the AFL problem. The DOLDA model was designed with the AFL problem in mind, since it has the exact structure of a mix of nominal and numeric inputs in combination with unstructured text. We show that our DOLDA model exhibits many nice properties, among others, interpretability, that the research community has iden- tified as missing in current models for AFL.
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| 44. |
- Kim, Hokeun, et al.
(författare)
-
A Predictable and Command- Level Priority-Based DRAM Controller for Mixed-Criticality Systems
- 2015
-
Ingår i: Proceedings of the 21th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS). - : IEEE Press. - 9781479986033 ; , s. 317-326
-
Konferensbidrag (refereegranskat)abstract
- Mixed-criticality systems have tasks with different criticality levels running on the same hardware platform. Today's DRAM controllers cannot adequately satisfy the often conflicting requirements of tightly bounded worst-case latency for critical tasks and high performance for non-critical real-time tasks. We propose a DRAM memory controller that meets these requirements by using bank-aware address mapping and DRAM command-level priority-based scheduling with preemption. Many standard DRAM controllers can be extended with our approach, incurring no performance penalty when critical tasks are not generating DRAM requests. Our approach is evaluated by replaying memory traces obtained from executing benchmarks on an ARM ISA-based processor with caches, which is simulated on the gem5 architecture simulator. We compare our approach against previous TDM-based approaches, showing that our proposed memory controller achieves dramatically higher performance for non-critical tasks, without any significant impact on the worstcase latency of critical tasks.
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| 45. |
- Kim, Hokeun, et al.
(författare)
-
A Toolkit for Construction of Authorization Service Infrastructure for the Internet of Things
- 2017
-
Ingår i: Internet-of-Things Design and Implementation (IoTDI), 2017 IEEE/ACM Second International Conference on. - New York, NY, USA : ACM Digital Library. ; , s. 147-158
-
Konferensbidrag (refereegranskat)abstract
- The challenges posed by the Internet of Things (IoT) render existing security measures ineffective against emerging networks and devices. These challenges include heterogeneity, operation in open environments, and scalability. In this paper, we propose SST (Secure Swarm Toolkit), an open-source toolkit for construction and deployment of an authorization service infrastructure for the IoT. The infrastructure uses distributed local authorization entities, which provide authorization services that can address heterogeneous security requirements and resource constraints in the IoT. The authorization services can be accessed by network entities through software interfaces provided by SST, called accessors. The accessors enable IoT developers to readily integrate their devices with authorization services without needing to manage cryptographic keys and operations. To rigorously show that SST provides necessary security guarantees, we have performed a formal security analysis using an automated verification tool. In addition, we demonstrate the scalability of our approach with a mathematical analysis, as well as experiments to evaluate security overhead of network entities under different security profiles supported by SST
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| 46. |
- Kim, H., et al.
(författare)
-
An Architectural Mechanism for Resilient IoT Services
- 2017
-
Ingår i: SafeThings 2017 - Proceedings of the 1st ACM International Workshop on the Internet of Safe Things, Part of SenSys 2017. - New York, NY, USA : Association for Computing Machinery (ACM). - 9781450354790 ; , s. 8-13
-
Konferensbidrag (refereegranskat)abstract
- Availability of authentication and authorization services is critical for the safety of the Internet of Things (IoT). By leveraging an emerging network architecture based on edge computers, IoT’s availability can be protected even under situations such as network failures or denial-of-service (DoS) attacks. However, little has been explored for the issue of sustaining availability even when edge computers fail. In this paper, we propose an architectural mechanism for enhancing the availability of the authorization infrastructure for the IoT. The proposed approach leverages a technique called secure migration, which allows IoT devices to migrate to other local authorization entities served in trusted edge computers when their authorization entity becomes unavailable. Specifically, we point out necessary considerations for planning secure migration and present automated migration policy construction and protocols for preparing and executing the migration. The effectiveness of our approach is illustrated using a concrete application of smart buildings and network simulation, where our proposed solution achieves significantly higher availability in case of failures in some of the authorization entities.
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| 47. |
- Kim, Hokeun, et al.
(författare)
-
Resilient Authentication and Authorization for the Internet of Things (IoT) Using Edge Computing
- 2020
-
Ingår i: ACM Transactions on Internet of Things. - : ACM Press. - 2691-1914 .- 2577-6207. ; 1:1, s. -27
-
Tidskriftsartikel (refereegranskat)abstract
- An emerging type of network architecture called edge computing has the potential to improve the availability and resilience of IoT services under anomalous situations such as network failures or denial-of-service (DoS) attacks. However, relatively little has been explored on the problem of ensuring availability even when edge computers that provide key security services (e.g., authentication and authorization) become unavailable themselves. This article proposes a resilient authentication and authorization framework to enhance the availability of IoT services under DoS attacks or failures. The proposed approach leverages a technique called secure migration, which allows an IoT device to migrate to another trusted edge computer when its own local authorization service becomes unavailable. Specifically, we describe the design of a secure migration framework and its supporting mechanisms, including (1) automated migration policy construction and (2) protocols for preparing and executing the secure migration. We formalize secure migration policy con- struction as an integer linear programming (ILP) problem and show its effectiveness using a case study on smart buildings, where the proposed solution achieves significantly higher availability under simulated at- tacks on authorization services.
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| 48. |
- Kim, Y., et al.
(författare)
-
Wcet-aware function-level dynamic code management on Scratchpad memory
- 2017
-
Ingår i: ACM Transactions on Embedded Computing Systems. - : Association for Computing Machinery. - 1539-9087 .- 1558-3465. ; 16:4
-
Tidskriftsartikel (refereegranskat)abstract
- Scratchpad memory (SPM) is a promising on-chip memory choice in real-time and cyber-physical systems where timing is of the utmost importance. SPM has time-predictable characteristics since its data movement between the SPM and the main memory is entirely managed by software. One way of such management is dynamic management. In dynamic management of instruction SPMs, code blocks are dynamically copied from the main memory to the SPM at runtime by executing direct memory access (DMA) instructions. Code management techniques try to minimize the overhead of DMA operations by finding an allocation scheme that leads to efficient utilization. In this article, we present three function-level code management techniques. These techniques perform allocation at the granularity of functions, with the objective of minimizing the impact of DMA overhead to the worst-case execution time (WCET) of a given program. The first technique finds an optimal mapping of each function to a region using integer linear programming (ILP), whereas the second technique is a polynomial-time heuristic that is suboptimal. The third technique maps functions directly to SPM addresses, not using regions, which can further reduce the WCET. Based on ILP, it can also find an optimal mapping. We evaluate our techniques using the Mälardalen WCET suite, MiBench suite, and proprietary automotive applications from industry. The results show that our techniques can significantly reduce the WCET estimates compared to caches with the state-of-the-art cache analysis.
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| 49. |
- Kozma, Viktor, et al.
(författare)
-
MORAP : a Modular Robotic Arm Platform for Teaching and Experimenting with Equation-based Modeling Languages [Work in Progress]
- 2016
-
Ingår i: Proceedings of 7th International Workshop on Equation-Based Object-Oriented Modeling Languages and Tools (EOOLT). - New York, NY, USA : ACM Digital Library. - 9781450342025 ; , s. 27-30
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Konferensbidrag (refereegranskat)abstract
- Equation-based object-oriented (EOO) modeling and simu- lation techniques have in the last decades gained significant attention both in academia and industry. One of the key properties of EOO languages is modularity, where different components can be developed independently and then connected together to form a complete acausal model. However, extensive modeling without explicit model validation together with a real physical system can result in incorrect assumptions and false conclusions. In particular, in an educational and research setting, it is vital that students experiment both with equation-based models and the real system that is being modeled. In this work-in-progress paper, we present a physical experimental robotic arm platform that is designed for teaching and research. Similar to EOO models, the robotic arm is modular, meaning that its parts can be reconfigured and composed together in various settings, and used for different experiments. The platform is completely open source, where electronic schematics, CAD models for 3D printing, controller software, and component specifications are available on GitHub. The vision is to form a community, where new open source components are continuously added, to enable an open and freely available physical experimental platform for EOO languages.
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- Lohstroh, Marten, et al.
(författare)
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Logical Time for Reactive Software
- 2023
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Ingår i: Proceedings of 2023 Cyber-Physical Systems and Internet-of-Things Week, CPS-IoT Week 2023. - : Association for Computing Machinery (ACM). ; , s. 313-318
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Konferensbidrag (refereegranskat)abstract
- Timing is an essential feature of reactive software. It is not just a performance metric, but rather forms a core part of the semantics of programs. This paper argues for a notion of logical time that serves as an engineering model to complement a notion of physical time, which models the physical passage of time. Programming models that embrace logical time can provide deterministic concurrency, better analyzability, and practical realizations of timing-sensitive applications. We give definitions for physical and logical time and review some languages and formalisms that embrace logical time.
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