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vorgelegt von

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Most temporal logics which have been introduced and studied in the past decades can be embedded into the modal L µ. This is the case for e.g. PDL, CTL, CTL ∗ , ECTL, LTL, etc. and entails that these logics cannot express non-regular program properties. In recent years, some novel approaches towards an increase in expressive power have been made:...

Most temporal logics which have been introduced and studied in the past decades can be embedded into the modal L µ. This is the case for e.g. PDL, CTL, CTL ∗ , ECTL, LTL, etc. and entails that these logics cannot express non-regular program properties. In recent years, some novel approaches towards an increase in expressive power have been made: Fixpoint Logic with Chop enriches L µ with a sequential composition operator and thereby allows to characterise context-free processes. The Modal Iteration Calculus uses inflationary fixpoints to exceed the expressive power of L µ. Higher-Order Fixpoint Logic (HFL) incorporates a simply typed λ-calculus into a setting with extremal fixpoint operators and even exceeds the expressive power of Fixpoint Logic with Chop. But also PDL has been equipped with context-free programs instead of regular ones. In terms of expressivity there is a natural demand for richer frameworks since program property specifications are simply not limited to the regular sphere. Expressivity however usually comes at the price of an increased computational complexity of logic-related decision problems. For instance are the satisfiability problems for the above mentioned logics Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2012-06-25

Source:

http://edoc.ub.uni-muenchen.de/11677/1/Axelsson_Roland.pdf

http://edoc.ub.uni-muenchen.de/11677/1/Axelsson_Roland.pdf Minimize

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text

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en

DDC:

005 Computer programming, programs & data *(computed)*

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Title:

The complexity of model checking higher-order fixpoint logic

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Abstract. Higher-Order Fixpoint Logic (HFL) is a hybrid of the simply typed λ-calculus and the modal µ-calculus. This makes it a highly expressive temporal logic that is capable of expressing various interesting correctness properties of programs that are not expressible in the modal µ-calculus. This paper provides complexity results for its mod...

Abstract. Higher-Order Fixpoint Logic (HFL) is a hybrid of the simply typed λ-calculus and the modal µ-calculus. This makes it a highly expressive temporal logic that is capable of expressing various interesting correctness properties of programs that are not expressible in the modal µ-calculus. This paper provides complexity results for its model checking problem. In particular we consider its fragments HFL k,m which are formed using types of bounded order k and arity m only. We establish kExpTime-completeness for model checking each HFL k,m fragment. For the upper bound we use fixpoint elimination to obtain reachability games that are singly-exponential in the size of the formula and k-fold exponential in the size of the underlying transition system. These games can be solved in deterministic linear time. As a simple consequence we obtain an ExpTime upper bound on the expression complexity of each HFL k,m. The lower bound is established by a reduction from the word problem for alternating (k − 1)-fold exponential space bounded Turing Machines. Since there are fixed machines of that type whose word problems are kExpTime-hard already we obtain, as a corollary, kExpTime-completeness for the data complexity of HFL k,m already when m ≥ 4. This also yields a hierarchy result in expressive power. 1. Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2013-08-04

Source:

http://arxiv.org/pdf/0704.3931v1.pdf

http://arxiv.org/pdf/0704.3931v1.pdf Minimize

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text

Language:

en

DDC:

005 Computer programming, programs & data *(computed)*

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Title:

THE COMPLEXITY OF MODEL CHECKING HIGHER ORDER FIXPOINT LOGIC

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Abstract. Higher Order Fixpoint Logic (HFL) is a hybrid of the simply typed λ-calculus and the modal µ-calculus. This makes it a highly expressive temporal logic that is capable of expressing various interesting correctness properties of programs that are not expressible in the modal µ-calculus. This paper provides complexity results for its mod...

Abstract. Higher Order Fixpoint Logic (HFL) is a hybrid of the simply typed λ-calculus and the modal µ-calculus. This makes it a highly expressive temporal logic that is capable of expressing various interesting correctness properties of programs that are not expressible in the modal µ-calculus. This paper provides complexity results for its model checking problem. In particular we consider its fragments HFL k,m which are formed using types of bounded order k and arity m only. We establish kExpTime-completeness for model checking each HFL k,m fragment. For the upper bound we use fixpoint elimination to obtain reachability games that are singly-exponential in the size of the formula and k-fold exponential in the size of the underlying transition system. These games can be solved in deterministic linear time. As a simple consequence we obtain an ExpTime upper bound on the expression complexity of each HFL k,m. The lower bound is established by a reduction from the word problem for alternating (k − 1)-fold exponential space bounded Turing Machines. Since there are fixed machines of that type whose word problems are kExpTime-hard already we obtain, as a corollary, kExpTime-completeness for the data complexity of HFL k,m already when m ≥ 4. This also yields a hierarchy result in expressive power. 1. Minimize

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The Pennsylvania State University CiteSeerX Archives

Year of Publication:

2008-07-01

Source:

http://www.tcs.informatik.uni-muenchen.de/~axelsson/paper/lmcs-2007.pdf

http://www.tcs.informatik.uni-muenchen.de/~axelsson/paper/lmcs-2007.pdf Minimize

Document Type:

text

Language:

en

DDC:

005 Computer programming, programs & data *(computed)*

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Metadata may be used without restrictions as long as the oai identifier remains attached to it.

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Title:

Verification of Non-Regular Program Properties

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Most temporal logics which have been introduced and studied in the past decades can be embedded into the modal mu-calculus. This is the case for e.g. PDL, CTL, CTL*, ECTL, LTL, etc. and entails that these logics cannot express non-regular program properties. In recent years, some novel approaches towards an increase in expressive power have been...

Most temporal logics which have been introduced and studied in the past decades can be embedded into the modal mu-calculus. This is the case for e.g. PDL, CTL, CTL*, ECTL, LTL, etc. and entails that these logics cannot express non-regular program properties. In recent years, some novel approaches towards an increase in expressive power have been made: Fixpoint Logic with Chop enriches the mu-calculus with a sequential composition operator and thereby allows to characterise context-free processes. The Modal Iteration Calculus uses inflationary fixpoints to exceed the expressive power of the mu-calculus. Higher-Order Fixpoint Logic (HFL) incorporates a simply typed lambda-calculus into a setting with extremal fixpoint operators and even exceeds the expressive power of Fixpoint Logic with Chop. But also PDL has been equipped with context-free programs instead of regular ones. In terms of expressivity there is a natural demand for richer frameworks since program property specifications are simply not limited to the regular sphere. Expressivity however usually comes at the price of an increased computational complexity of logic-related decision problems. For instance are the satisfiability problems for the above mentioned logics undecidable. We investigate in this work the model checking problem of three different logics which are capable of expressing non-regular program properties and aim at identifying fragments with feasible model checking complexity. Firstly, we develop a generic method for determining the complexity of model checking PDL over arbitrary classes of programs and show that the border to undecidability runs between PDL over indexed languages and PDL over context-sensitive languages. It is however still in PTIME for PDL over linear indexed languages and in EXPTIME for PDL over indexed languages. We present concrete algorithms which allow implementations of model checkers for these two fragments. We then introduce an extension of CTL in which the UNTIL- and RELEASE- operators are adorned with formal languages. These are interpreted over labeled paths and restrict the moments on such a path at which the operators are satisfied. The UNTIL-operator is for instance satisfied if some path prefix forms a word in the language it is adorned with (besides the usual requirement that until that moment some property has to hold and at that very moment some other property must hold). Again, we determine the computational complexities of the model checking problems for varying classes of allowed languages in either operator. It turns out that either enabling context-sensitive languages in the UNTIL or context-free languages in the RELEASE- operator renders the model checking problem undecidable while it is EXPTIME-complete for indexed languages in the UNTIL and visibly pushdown languages in the RELEASE- operator. PTIME-completeness is a result of allowing linear indexed languages in the UNTIL and deterministic context-free languages in the RELEASE. We do also give concrete model checking algorithms for several interesting fragments of these logics. Finally, we turn our attention to the model checking problem of HFL which we have already studied in previous works. On finite state models it is k-EXPTIME-complete for HFL(k), the fragment of HFL obtained by restricting functions in the lambda-calculus to order k. Novel in this work is however the generalisation (from the first-order case to the case for functions of arbitrary order) of an idea to improve the best and average case behaviour of a model checking algorithm by using partial functions during the fixpoint iteration guided by the neededness of arguments. This is possible, because the semantics of a closed HFL formula is not a total function but the value of a function at some argument. Again, we give a concrete algorithm for such an improved model checker and argue that despite the very high model checking complexity this improvement is very useful in practice and gives feasible results for HFL with lower order fuctions, backed up by a statistical analysis of the number of needed arguments on a concrete example. Furthermore, we show how HFL can be used as a tool for the development of algorithms. Its high expressivity allows to encode a wide variety of problems as instances of model checking already in the first-order fragment. The rather unintuitive -- yet very succinct -- problem encoding together with an analysis of the behaviour of the above sketched optimisation may give deep insights into the problem. We demonstrate this on the example of the universality problem for nondeterministic finite automata, where a slight variation of the optimised model checking algorithm yields one of the best known methods so far which was only discovered recently. We do also investigate typical model-theoretic properties for each of these logics and compare them with respect to expressive power. Minimize

Publisher:

Ludwig-Maximilians-Universität München

Year of Publication:

2010-06-25

Document Type:

Dissertation ; NonPeerReviewed

Subjects:

Fakultät für Mathematik ; Informatik und Statistik

Fakultät für Mathematik ; Informatik und Statistik Minimize

DDC:

005 Computer programming, programs & data *(computed)*

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Title:

IP packet prioritiser for low bandwidth links

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Mongolia is a country where the development of the digital infrastructure started very recently. It is a large country with almost no installed fibre optics and a very old and unreliable telephone network. Datacom Co., Ltd. is the largest company providing computer networks in Mongolia. They have already connected the country to the Inte...

Mongolia is a country where the development of the digital infrastructure started very recently. It is a large country with almost no installed fibre optics and a very old and unreliable telephone network. Datacom Co., Ltd. is the largest company providing computer networks in Mongolia. They have already connected the country to the Internet via a satellite link and they are providing Internet access to companies, universities, the government and private people. They are currently working on connecting all the country provinces to the Internet via satellite links. They also aim to provide phone and fax services in these areas. To provide phone service over a satellite link using the Internet protocol, Datacom needs some kind of bandwidth allocation and bandwidth guarantee system to provide the customers with a service of acceptable quality. The purpose of this thesis project was to design an IP bandwidth allocation system suitable for Datacom and Mongolia. Such systems can already be bought from several different companies, but what Datacom needs is a low-cost and efficient system which suits its specific needs. The result is a small IP packet prioritiser which can be installed in almost any IBM PC compatible computer running the Linux operating system. This package can be used to prioritise not only IP voice applications, but all different kinds of IP traffic. Two user programs to manage the system have also been implemented: one simple command line application and one with a graphical interface which can be used over a network. Test shows that the performance of the IP packet prioritiser is good. It makes it possible to control IP traffic over a low bandwidth link. Doing so does not significantly reduce the throughput or increase the delay over the link. Unfortunately, no tests could bedone on a real satellite link, but the IP packet prioritiser works fine on a similar network. Minimize

Publisher:

Luleå/Systemteknik

Contributors:

Degermark, Mikael

Year of Publication:

2000

Document Type:

H3

Language:

eng

Subjects:

bandbreddsbegränsning ; bandwidth management

bandbreddsbegränsning ; bandwidth management Minimize

DDC:

303 Social processes *(computed)*

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Master of Science in Engineering Technology ; Civilingenjörsexamen

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Title:

Early nasogastric feeding in predicted severe acute pancreatitis: a clinical, randomized study.

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Objective: To compare the efficacy and safety of early, nasogastric enteral nutrition (EN) with total parenteral nutrition (TPN) in patients with predicted severe acute pancreatitis (SAP). Summary Background Data: In SAP, the magnitude of the inflammatory response as well as increased intestinal permeability correlates with outcome. Enteral feed...

Objective: To compare the efficacy and safety of early, nasogastric enteral nutrition (EN) with total parenteral nutrition (TPN) in patients with predicted severe acute pancreatitis (SAP). Summary Background Data: In SAP, the magnitude of the inflammatory response as well as increased intestinal permeability correlates with outcome. Enteral feeding has been suggested superior to parenteral feeding due to a proposed beneficial effect on the gut barrier. Methods: Fifty patients who met the inclusion criteria were randomized to TPN or EN groups. The nutritional regimen was started within 24 hours from admission and EN was provided through a nasogastric tube. The observation period was 10 days. Intestinal permeability was measured by excretion of polyethylene glycol (PEG) and concentrations of antiendotoxin core antibodies (Endocab). Interieukins (IL)-6 IL-8, and C-reactive protein (CRP) were used as markers of the systemic inflammatory response. Morbidity and feasibility of the nutritional route were evaluated by the frequency of complications, gastrointestinal symptoms, and abdominal pain. Results: PEG, Endocab, CRP, IL-6, APACHE II score, severity according to the Atlanta classification (22 patients), and gastrointestinal symptoms or abdominal pain did not significantly differ between the groups. The incidence of hyperglycemia was significantly higher in TPN patients (21 of 26 vs. 7 of 23; P < 0.001). Total complications (25 vs. 52; P = 0.04) and pulmonary complications (10 vs. 21; P = 0.04) were significantly more frequent in EN patients, although complications were diagnosed dominantly within the first 3 days. Conclusion: In predicted SAP, nasogastric early EN was feasible and resulted in better control of blood glucose levels, although the overall early complication rate was higher in the EN group. No beneficial effects on intestinal permeability or the inflammatory response were seen by EN treatment. Minimize

Publisher:

Lippinkott Williams & Wilkins

Year of Publication:

2006

Document Type:

text

Language:

eng

Subjects:

Medicine and Health Sciences

Medicine and Health Sciences Minimize

DDC:

610 Medicine & health *(computed)*

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Title:

The Complexity of Model Checking Higher-Order Fixpoint Logic

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Higher-Order Fixpoint Logic (HFL) is a hybrid of the simply typed \lambda-calculus and the modal \lambda-calculus. This makes it a highly expressive temporal logic that is capable of expressing various interesting correctness properties of programs that are not expressible in the modal \lambda-calculus. This paper provides complexity results for...

Higher-Order Fixpoint Logic (HFL) is a hybrid of the simply typed \lambda-calculus and the modal \lambda-calculus. This makes it a highly expressive temporal logic that is capable of expressing various interesting correctness properties of programs that are not expressible in the modal \lambda-calculus. This paper provides complexity results for its model checking problem. In particular we consider those fragments of HFL built by using only types of bounded order k and arity m. We establish k-fold exponential time completeness for model checking each such fragment. For the upper bound we use fixpoint elimination to obtain reachability games that are singly-exponential in the size of the formula and k-fold exponential in the size of the underlying transition system. These games can be solved in deterministic linear time. As a simple consequence, we obtain an exponential time upper bound on the expression complexity of each such fragment. The lower bound is established by a reduction from the word problem for alternating (k-1)-fold exponential space bounded Turing Machines. Since there are fixed machines of that type whose word problems are already hard with respect to k-fold exponential time, we obtain, as a corollary, k-fold exponential time completeness for the data complexity of our fragments of HFL, provided m exceeds 3. This also yields a hierarchy result in expressive power. ; Comment: 33 pages, 2 figures, to be published in Logical Methods in Computer Science Minimize

Year of Publication:

2007-04-30

Document Type:

text

Subjects:

Computer Science - Logic in Computer Science ; F.3.1 ; F.4.1

Computer Science - Logic in Computer Science ; F.3.1 ; F.4.1 Minimize

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005 Computer programming, programs & data *(computed)*

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Title:

Tissue factor in predicted severe acute pancreatitis

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AIM: To study tissue factor (TF) in acute pancreatitis and evaluate the role of TF as a predictive marker of severity.

AIM: To study tissue factor (TF) in acute pancreatitis and evaluate the role of TF as a predictive marker of severity. Minimize

Publisher:

Baishideng Publishing Group Co., Limited

Year of Publication:

2010-12-28

Document Type:

Text

Language:

en

Subjects:

Brief Article

Brief Article Minimize

Rights:

©2010 Baishideng Publishing Group Co., Limited. All rights reserved.

©2010 Baishideng Publishing Group Co., Limited. All rights reserved. Minimize

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Title:

Early Nasogastric Feeding in Predicted Severe Acute Pancreatitis: A Clinical, Randomized Study

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Early, nasogastric enteral nutrition in patients with predicted severe acute pancreatitis was feasible and resulted in better blood-glucose control as compared with isocaloric total parenteral nutrition. No benefits on intestinal permeability or the acute inflammatory response were seen by enteral nutrition.

Early, nasogastric enteral nutrition in patients with predicted severe acute pancreatitis was feasible and resulted in better blood-glucose control as compared with isocaloric total parenteral nutrition. No benefits on intestinal permeability or the acute inflammatory response were seen by enteral nutrition. Minimize

Year of Publication:

2006-12

Document Type:

Text

Language:

en

Subjects:

Original Articles and Discussions

Original Articles and Discussions Minimize

Rights:

© 2006 Lippincott Williams & Wilkins, Inc.

© 2006 Lippincott Williams & Wilkins, Inc. Minimize

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Title:

Extended Computation Tree Logic

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We introduce a generic extension of the popular branching-time logic CTL which refines the temporal until and release operators with formal languages. For instance, a language may determine the moments along a path that an until property may be fulfilled. We consider several classes of languages leading to logics with different expressive power ...

We introduce a generic extension of the popular branching-time logic CTL which refines the temporal until and release operators with formal languages. For instance, a language may determine the moments along a path that an until property may be fulfilled. We consider several classes of languages leading to logics with different expressive power and complexity, whose importance is motivated by their use in model checking, synthesis, abstract interpretation, etc. We show that even with context-free languages on the until operator the logic still allows for polynomial time model-checking despite the significant increase in expressive power. This makes the logic a promising candidate for applications in verification. In addition, we analyse the complexity of satisfiability and compare the expressive power of these logics to CTL* and extensions of PDL. Minimize

Year of Publication:

2010-06-18

Document Type:

text

Subjects:

Computer Science - Logic in Computer Science

Computer Science - Logic in Computer Science Minimize

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