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Safety, Security, and Semantic Aspects of Equation-Based Object-Oriented Languages and Environments
Linköping University, Department of Computer and Information Science, PELAB - Programming Environment Laboratory. Linköping University, The Institute of Technology.
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Institutionen för datavetenskap , 2007. , 26 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1337
Keyword [en]
Modeling, Simulation, Equation-Based, Object-Oriented, Modelica, Type System, Semantics, Language Safety, Secure Simulation
National Category
Computer Science
Identifiers
URN: urn:nbn:se:liu:diva-10134ISBN: 978-91-85895-24-3 (print)OAI: oai:DiVA.org:liu-10134DiVA: diva2:16882
Presentation
2007-12-07, Visionen, B, Linköpings universistet, Linköping, 13:15 (English)
Opponent
Supervisors
Note
Report code: LIU-TEK-LIC-2007:46. On the day of the defence date the status of article IV was: In Progress; The status of article V was: Manuscript.Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2014-10-08
List of papers
1. Types in the Modelica Language
Open this publication in new window or tab >>Types in the Modelica Language
2006 (English)Conference paper, Published paper (Other academic)
Abstract [en]

 

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 com-

pilers 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 Model-

ica 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 defin-

ition.

 

Keyword
type system; types; Modelica; simulation; modeling; type safety
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12698 (URN)
Conference
Proceedings of the Fifth International Modelica Conference, Vienna 2006
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2014-10-08
2. Determining Over- and Under-Constrained Systems of Equations using Structural Constraint Delta
Open this publication in new window or tab >>Determining Over- and Under-Constrained Systems of Equations using Structural Constraint Delta
2006 (English)Conference paper, Published paper (Other academic)
Abstract [en]

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.

Keyword
equation-based, modeling, object-oriented, over-constrained, separate compilation, type checking, under-constrained, simulation languages, algorithms
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12699 (URN)10.1145/1173706.1173729 (DOI)
Conference
Proceedings of the 5th International Conference on Generative Programming and Component Engineering
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2014-10-08
3. Abstract Syntax Can Make the Definition of Modelica Less Abstract
Open this publication in new window or tab >>Abstract Syntax Can Make the Definition of Modelica Less Abstract
2007 (English)In: Proceedings of the 1st International Workshop on Equation-Based Object-Oriented Languages and Tools, Berlin, Germany, 2007, 111-126 p.Conference paper, Published paper (Refereed)
Abstract [en]

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.

National Category
Computer Science
Identifiers
urn:nbn:se:liu:diva-12700 (URN)978-91-7519-822-4 (ISBN)
Conference
1st International Workshop on Equation-Based Object-Oriented Languages and Tools
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2014-10-08
4. Secure Distributed Co-Simulation over Wide Area Networks
Open this publication in new window or tab >>Secure Distributed Co-Simulation over Wide Area Networks
Show others...
2007 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Modeling and simulation often require different tools for specialized purposes, which increase the motivation to use co-simulation. Since physical models often are describing enterprises¿ primary know-how, there is a need for a sound approach to securely perform modeling and simulation. This paper discusses different possibilities from a security perspective, with focus on secure distributed co-simulation over wide area networks (WANs), using transmission line modeling (TLM). An approach is outlined and performance is evaluated both in a simulated WAN environment, and for a real encrypted co-simulation between Sweden and Australia. It is concluded that several parameters affect the total simulation time, where especially the network delay (latency) has a significant impact.

National Category
Computer Science
Identifiers
urn:nbn:se:liu:diva-12701 (URN)
Conference
Proceedings of the 48th Conference on Simulation and Modelling (SIMS'07), Gothenburg, Sweden
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2014-10-08
5. Flow Lambda Calculus for Declarative Physical Connection Semantics
Open this publication in new window or tab >>Flow Lambda Calculus for Declarative Physical Connection Semantics
2007 (English)Report (Other academic)
Abstract [en]

One of the most fundamental language constructs of equation-based object-oriented languages is the possibility to state acausal connections, where both potential variables and flow variables exist. Several of the state-of-the art languages in this category are informally specified using natural language. This can make the languages hard to interpret, reason about, and disable the possibility to guarantee the absence of certain errors. In this work, we construct a formal operational small-step semantics based on the lambda-calculus. The calculus is then extended with more convenient modeling capabilities. Examples are given that demonstrate the expressiveness of the language, and some tests are made to verify the correctness of the semantics.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2007. 18 p.
Series
Technical reports in Computer and Information Science, ISSN 1654-7233 ; 1
Keyword
Flow connection, Flow Lambda Calculus, Operational Semantics
National Category
Computer Science
Identifiers
urn:nbn:se:liu:diva-12702 (URN)
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2010-11-03Bibliographically approved

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Broman, David

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