@string{brics =	"{BRICS}"}
@string{daimi =	"Department of Computer Science, University of Aarhus"}
@string{iesd  =	"Department of Computer Science, Institute
		  of Electronic Systems, Aalborg University"}
@string{rs    =	"Research Series"}
@string{ns    =	"Notes Series"}
@string{ls    =	"Lecture Series"}
@string{ds    =	"Dissertation Series"}

  author = 	 "Sunesen, Kim",
  title = 	 "Reasoning about Reactive Systems",
  institution =  brics,
  year = 	 1998,
  type = 	 ds,
  number = 	 "DS-98-3",
  address = 	 daimi,
  month = 	 dec,
  note =	 "PhD thesis. xvi+204~pp",
  abstract =	 "The main concern of this thesis is the formal reasoning
		  about reactive systems.\bibpar

		  We first consider the automated verification of safety
		  properties of finite systems.  We propose a practical
		  framework for integrating the behavioural reasoning about
		  distributed reactive systems with model-checking methods.
		  We devise a small self-contained theory of distributed
		  reactive systems including standard concepts like
		  implementation, abstraction, and proof methods for
		  compositional reasoning.  The proof methods are based on
		  trace abstractions that relate the behaviours of the
		  program with the specification.  We show that trace
		  abstractions and the proof methods can be expressed in a
		  decidable Monadic Second-Order Logic (M2L) on words.  To
		  demonstrate the practical pertinence of the approach, we
		  give a self-contained, introductory account of the method
		  applied to an RPC-memory specification problem proposed
		  by Broy and Lamport.  The purely behavioural descriptions
		  which we formulate from the informal specifications are
		  written in the high-level symbolic language FIDO, a
		  syntactic extension of M2L.  Our solution involves
		  FIDO-formulas more than 10 pages long.  They are
		  translated into M2L-formulas of length more than 100
		  pages which are decided automatically within minutes.
		  Hence, our work shows that complex behaviours of reactive
		  systems can be formulated and reasoned about without
		  explicit state-based programming, and moreover that
		  temporal properties can be stated succinctly while
		  enjoying automated analysis and verification.\bibpar

		  Next, we consider the theoretical borderline of
		  decidability of behavioural equivalences for
		  infinite-state systems.  We provide a systematic study of
		  the decidability of non-interleaving linear-time
		  behavioural equivalences for infinite-state systems
		  defined by CCS and TCSP style process description
		  languages.  We compare standard language equivalence with
		  two generalisations based on the predominant approaches
		  for capturing non-interleaving behaviour: pomsets
		  representing global causal dependency, and locality
		  representing spatial distribution of events.  Beginning
		  with the process calculus of Basic Parallel Processes
		  (BPP) obtained as a minimal concurrent extension of
		  finite processes, we systematically investigate
		  extensions towards full CCS and TCSP.  Our results show
		  that whether a non-interleaving equivalence is based on
		  global causal dependency between events or whether it is
		  based on spatial distribution of events can have an
		  impact on decidability.  Furthermore, we investigate
		  tau-forgetting versions of the two non-interleaving
		  equivalences, and show that for BPP they are

		  Finally, we address the issue of synthesising distributed
		  systems -- modelled as elementary net systems -- from
		  purely sequential behaviours represented by
		  synchronisation trees.  Based on the notion of regions,
		  Ehrenfeucht and Rozenberg have characterised the
		  transition systems that correspond to the behaviour of
		  elementary net systems.  Building upon their results, we
		  characterise the synchronisation trees that correspond to
		  the behaviour of active elementary net systems, that is,
		  those in which each condition can always cease to hold.
		  The identified class of synchronisation trees is
		  definable in a monadic second order logic over infinite
		  trees.  Hence, our work provides a theoretical foundation
		  for smoothly combining techniques for the synthesis of
		  nets from transition systems with the synthesis of
		  synchronisation trees from logical specifications",
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  author = 	 "Lassen, S{\o}ren B.",
  OPTauthor = 	 "Lassen, S{\o}ren B{\o}gh",
  title = 	 "Relational Reasoning about Functions and Nondeterminism",
  institution =  brics,
  year = 	 1998,
  type = 	 ds,
  number = 	 "DS-98-2",
  address = 	 daimi,
  month = 	 dec,
  note =	 "PhD thesis. x+126~pp",
  abstract =	 "This dissertation explores a uniform, relational proof
		  style for operational arguments about program
		  equivalences.  It improves and facilitates many
		  previously given proofs, and it is used to establish new
		  proof rules for reasoning about term contexts, recursion,
		  and nondeterminism in higher-order programming

		  Part I develops an algebra of relations on terms and
		  exploits these relations in operational arguments about
		  contextual equivalence for a typed deterministic
		  functional language.  Novel proofs of the basic laws,
		  sequentiality and continuity properties, induction rules,
		  and the CIU Theorem are presented together with new
		  relational proof rules akin to Sangiorgi's ``bisimulation
		  up to context'' for process calculi.\bibpar

		  Part II extends the results from the first part to
		  nondeterministic functional programs.  May and must
		  operational semantics and contextual equivalences are
		  defined and their properties are explored by means of
		  relational techniques.  For must contextual equivalence,
		  the failure of ordinary syntactic $\omega$-continuity in
		  the presence of countable nondeterminism is addressed by
		  a novel transfinite syntactic continuity principle.  The
		  relational techniques are also applied to the study of
		  lower and upper applicative simulation relations,
		  yielding new results about their properties in the
		  presence of countable and fair nondeterminism, and about
		  their relationship with the contextual equivalences",
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  author = 	 "Hougaard, Ole I.",
  OPTauthor = 	 "Ole Ildsgaard Hougaard",
  title = 	 "The {CLP(OIH)} Language",
  institution =  brics,
  year = 	 1998,
  type = 	 ds,
  number = 	 "DS-98-1",
  address = 	 daimi,
  month = 	 feb,
  note =	 "PhD thesis. xii+187~pp",
  abstract =	 "Many type inference problems are different instances of
		  the same constraint satisfaction problem. That is, there
		  is a class of constraints so that these type inference
		  problems can be reduced to the problem of finding a
		  solution to a set of constraints.  Furthermore, there is
		  an efficient constraint solving algorithm which can find
		  this solution in polynomial time.\bibpar

		  We have shown this by defining the appropriate constraint
		  domain, devising an efficient constraint satisfaction
		  algorithm, and designing a constraint logic programming
		  language over the constraint domain. We have implemented
		  an interpreter for the language and have thus produced a
		  tool which is well-suited for type inference problems of
		  different kinds.\bibpar

		  Among the problems that can be reduced to our constraint
		  domain are the following:

	     	  \item The simply typed $\lambda$-calculus.
	     	  \item The $\lambda$-calculus with subtyping.
	     	  \item Arbadi and Cardelli's Object calculus.
	     	  \item Effect systems for control flow analysis.
	     	  \item {\sf Turbo Pascal}.

		  With the added power of the constraint logic programming
		  language, certain type systems with no known efficient
		  algorithm can also be implemented --- e.g.\ the object
		  calculus with {\sf selftype}.\bibpar

		  The programming language thus provides a very easy way of
		  implementing a vast array of different type inference
  linkhtmlabs =	 "",
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