Prozesskalkule

Organisation

Prof. Dr. Manfred Schmidt-Schauß

Kunstliche Intelligenz und Softwaretechnologie

29. Januar 2008

Personen

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Prof. Dr. Manfred Schmidt-Schauß

◦ Zimmer 215

David Sabel

◦ Zimmer 216

◦ E-mail: sabel@ki.informatik.uni-frankfurt.de

Termine

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• 1 Vortrag jeweils

Dienstag, 14:00-16:00

in SR 307 (Informatik)

Homepage

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www.ki.informatik.uni-frankfurt.de/lehre/SS2008/PK

beinhaltet alle relevanten Informationen:

• Hinweise zur Ausarbeitung und Themenliste

• Terminplan

• aktuelle Bekanntmachungen

Leistungsschein

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Kriterien fur den Leistungsschein

• Regelmaßige Teilnahme

• Erfolgreicher Vortrag

• Akzeptierte Ausarbeitung

Vortrag

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• ca. 60min Dauer

• Gestaltungshinweise auf der WWW-Seite

• Prasentation:

- keine Kopie der Ausarbeitung!

- Beamer + Notebook

- Professur-Notebook: PDF, kein PowerPoint

Ausarbeitung

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• Abgabe zwei Wochen vor dem Vortrag

• Ausdruck und PDF

• Umfang ca. 15 Seiten

• vorherige Besprechung des Konzepts:Terminabsprache per E-Mail notwendig

• Hochstens eine Nachbesserung bis spatestenszwei Wochen nach dem Vortrag

Themen

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1Communicating Systems

In diesem Thema soll der”

Calculus of Communicating Systems“ (CCS) erortert werden.Er modelliert interaktive nicht-mobile Systeme. Aufbauend auf sequentiellen Automatenund einer Verhaltensgleichheit fur diese, werden nebenlaufige Prozesse und deren Aus-wertung behandelt. Abschließend wird eine Beobachtungsgleichheit definiert und derenAnwendbarkeit an Beispielen demonstriert.

Themen

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2The π-calculus: Syntax, Reduction, Behavioral

EquivalencesDer π-Kalkul ist eine Prozessalgebra. Hierbei kommunizieren Prozesse uber uber Kanaleund tauschen auf diese Art Kanalnamen untereinander aus. Fur dieses Thema sollzunachst die Syntax sowie die Auswertung des π-Kalkuls vorgestellt werden. Anschlie-ßend sollen grundlegende Verhaltensgleichheiten (barbed congruence, strong bisimilarity)fur den π-Kalkul erortert werden.

Themen

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3Polyadic π-calculus, Recursion, Variants of

BisimiliarityAufbauend auf dem vorherigen Thema sollen Erweiterungen des π-Kalkuls, wie der po-lyadische π-Kalkul und Rekursion fur den erortert werden. Zusatzlich sollen Variantender Verhaltensgleichheit vorgestellt werden.

Themen

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4Subcalculi of the π-calculus

Fur dieses Thema sollen eingeschrankte Varianten des π-Kalkuls (der asynchrone π-Kalkul und der

”localized“ π-Kalkul) sowie Verhaltensgleichheiten fur diese Kalkule be-

trachtet werden. Ferner sollen die Varianten bezuglich ihrer Ausdruckskraft gegenuberdem π-Kalkul verglichen werden.

Themen

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5Contextual equivalence for higher-order

pi-calculus revisitedThe higher-order pi-calculus is an extension of the pi-calculus to allow communicationof abstractions of processes rather than names alone. It has been studied intensively bySangiorgi in his thesis where a characterisation of a contextual equivalence for higher-order pi-calculus is provided using labelled transition systems and normal bisimulations.Unfortunately the proof technique used there requires a restriction of the language toonly allow finite types. We revisit this calculus and offer an alternative presentation ofthe labelled transition system and a novel proof technique which allows us to providea fully abstract characterisation of contextual equivalence using labelled transitions andbisimulations for higher-order pi-calculus with recursive types also.

Themen

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6Typed π-Calculi

Fur dieses Thema sollen verschiedene typisierte Varianten des π-Kalkuls erortert wer-den. Insbesondere der einfach getypte π-Kalkul, sowie der polymorph getypte π-Kalkul.Außerdem soll ein Einblick in getypte Verhaltensgleichheiten vermittelt werden.

Themen

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7The Join Calculus: A Language for Distributed

Mobile ProgrammingThe join calculus is a language that models distributed, mobile programming. It is cha-racterized by a formal notion of locality, a strict adherence to local synchronization, andits direct embedding of the ML programing language.Local synchronization means that messages always travel to a set destination, and canonly interact when they reach that destination; this is required for an efficient imple-mentation. The join calculus ML’s function bindings and pattern matching to specifyand program these synchronizations.Because of several remarkable identities, the rather complex theory of process equiva-lences admits some remarkable simplification when applied for the join calculus. Weprove several of these identities, and argue that equivalences for the join calculus canbe rationally organized into a five-tiered hierarchy.We present and illustrate the mobility extensions of the core calculus, which allow theprogramming of agent creation and migration. We briefly present how the calculus hasbeen extended to model distributed failures on the one hand, and cryptographic protocolson the other.

Themen

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8May and Must Testing in the Join-Calculus

The may and must-semantics are studied for the join-calculus. We provide a completecharacterization of may-testing through a restricted set of contexts. The same charac-terization, up-to the basic observations, is also proved to be complete with respect tothe must-testing semantics.

Themen

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9Mobile Ambients

We introduce a calculus describing the movement of processes and devices, includingmovement through administrative domains.

Themen

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10Observational Semantics for a Concurrent

Lambda Calculus with Reference Cells andFutures

We present an observational semantics for λ(fut), a concurrent λ-calculus with referencecells and futures. The calculus λ(fut) models the operational semantics of the concur-rent higher-order programming language Alice ML. Our result is a powerful notion ofequivalence that is the coarsest nontrivial congruence distinguishing observably differentprocesses. It justifies a maximal set of correct program transformations, and it includesλ(fut)’s deterministic reduction rules, in particular, call-by-value β-reduction.

Themen

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11On the representation of McCarthy’s amb in the

π-calculusWe study the encoding of λ , the call-by-name λ-calculus enriched with McCarthy’samb operator, into the π-calculus. Semantically, amb is a challenging operator, for thefairness constraints that it expresses. We prove that, under a certain interpretationof divergence in the λ-calculus (weak divergence), a faithful encoding is impossible.However, with a different interpretation of divergence (strong divergence), the encodingis possible, and for this case we derive results and coinductive proof methods to reasonabout λ that are similar to those for the encoding of pure λ-calculi. We then use thesemethods to derive the most important laws concerning amb. We take bisimilarity asbehavioural equivalence on the π-calculus, which sheds some light on the relationshipbetween fairness and bisimilarity.

Themen

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12An operational semantics for parallel lazy

evaluationWe present an operational semantics for parallel lazy evaluation that accurately modelsthe parallel behaviour of the non-strict parallel functional language GpH. Parallelismis modelled synchronously, that is, single reductions are carried out separately thencombined before proceeding to the next set of reductions. Consequently the semanticshas two levels, with transition rules for individual threads at one level and combining rulesat the other. Each parallel thread is modelled by a binding labelled with an indication ofits activity status. To the best of our knowledge this is the first semantics that modelssuch thread states. A set of labelled bindings corresponds to a heap and is used to modelsharing.The semantics is set at a higher level of abstraction than an abstract machine andis therefore more manageable for proofs about programs rather than implementations.At the same time, it is sufficiently low level to allow us to reason about programs interms of parallelism (i.e. the number of processors used) as well as work and run-timewith different numbers of processors.The framework used by the semantics is sufficientlyflexible and general that it can easily be adapted to express other evaluation models suchas sequential call-by-need, speculative evaluation, non-deterministic choice and others.

Themen

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13The Kell Calculus: A Family of Higher-Order

Distributed Process CalculiThis paper presents the Kell calculus, a family of distributed process calculi, parameteri-zed by languages for input patterns, that is intended as a basis for studying component-based distributed programming. The Kell calculus is built around a pi-calculus core, andfollows five design principles which are essential for a foundational model of distributedand mobile programming: hierarchical localities, local actions, higher-order communi-cation, programmable membranes, and dynamic binding. The paper discusses theseprinciples, and defines the syntax and operational semantics common to all calculi in theKell calculus family. The paper provides a co-inductive characterization of contextualequivalence for Kell calculi, under sufficient conditions on pattern languages, by meansof a form of higher-order bisimulation called strong context bisimulation. The paper alsocontains several examples that illustrate the expressive power of Kell calculi.

Themen

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14An Observational Theory for Mobile Ad Hoc

NetworksWe propose a process calculus to study the observational theory of Mobile Ad HocNetworks. The operational semantics of our calculus is given both in terms of a Re-duction Semantics and in terms of a Labelled Transition Semantics. We prove thatthe two semantics coincide. The labelled transition system is then used to derive thenotions of simulation and bisimulation for ad hoc networks. As a main result, we provethat the (weak) labelled bisimilarity completely characterises (weak) reduction barbedcongruence, a standard, branching-time, contextually-defined program equivalence. Wethen use our (bi)simulation proof methods to formally prove a number of non-trivialproperties of ad hoc networks.

Themen

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15An Input/Output Semantics for Distributed

Program Equivalence ReasoningA new notion of input/output equivalence of distributed imperative programs, with syn-chronous communications, is introduced. It preserves the input/output relation, encom-passing both, initial/final state and communication channel values. For its mathematicaljustification, the semantic framework of Manna and Pnueli, based on finite transitionsystems and reduced behaviors, is extended with the notion of input/output behavior.A set of laws for the equivalence is overviewed. A deduction rule for the substitutionof references to input/output equivalent procedures is defined and justified in the newsemantics. The rule is applied to decompose distributed program simplification proofs,introduced in a prior work, which use the laws to establish the equivalence between asequential and a parallel communicating program. They include communication elimi-nation as one of their steps. An outline of one of such proofs, for a pipelined processormodel, is included.

Themen

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16Temporal Logic

Fur dieses Thema soll die Temporal Logic als Werkzeug zur Spezifikation reaktiverSysteme erortert werden. Neben der Syntax und Semantik der temporalen Operatoren,sollen deren Eigenschaften und ein Herleitungssystem erlautert werden.