. We introduce a calculus for mobile agents and give its chemical semantics, with a precise definition for migration, failure, and failure detection. Various examples written in our calculus illustrate how to express remote executions, dynamic loading of remote resources and protocols with mobile agents. We give the encoding of our distributed calculus into the join-calculus. 1 Introduction It is not easy to match concurrency and distribution. Suppose, for instance, that we want to implement a concurrent calculus with CCS-like communication channels and with processes running on different physical sites. If we do not locate channels, we quickly face a global consensus problem for nearly every communication which uses the interconnection network. In a previous work [6], we introduced the join-calculus, an asynchronous variant of Milner's ß-calculus with better locality and better static scoping rules. It avoids global consensus and thus may be implemented in a realistic distributed en...

We demonstrate a physically-based technique for predicting the drape of a wide variety of woven fabrics. The approach exploits a theoretical model that explicitly represents the microstructure of woven cloth with interacting particles, rather than utilizing a continuum approximation. By testing a cloth sample in a Kawabata fabric testing device, we obtain data that is used to tune the model's energy functions, so that it reproduces the draping behavior of the original material. Photographs, comparing the drape of actual cloth with visualizations of simulation results, show that we are able to reliably model the unique large-scale draping characteristics of distinctly different fabric types. iii Figure 1.1: Draping cloth objects 1 Introduction The vast number of uses for cloth are mirrored in the extraordinary variety of types of woven fabrics. These range from the most exquisite fine silks, to the coarsest of burlaps, and are woven from such diverse fibers as natural wool and synth...

We study two encodings of the asynchronous #-calculus with input-guarded choice into its choice-free fragment. One encoding is divergence-free, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is fully abstract with respect to weak bisimulation, but the more natural divergence-free encoding is not. Instead, we show that it is fully abstract with respect to coupled simulation, a slightly coarser---but still coinductively defined---equivalence that does not enforce bisimilarity of internal branching decisions. The correctness proofs for the two choice encodings introduce a novel proof technique exploiting the properties of explicit decodings from translations to source terms.

The -calculus with synchronous output and mixed-guarded choices is strictly more expressive than the -calculus with asynchronous output and no choice. As a corollary, Palamidessi recently proved that there is no fully compositional encoding from the former into the latter that preserves divergence-freedom and symmetries. This paper shows

Constraint Logic Programming (CLP) is a new class of programming languages combining the declarativity of logic programming with the efficiency of constraint solving. New application areas, amongst them many different classes of combinatorial search problems such as scheduling, planning or resource allocation can now be solved, which were intractable for logic programming so far. The most important advantage that these languages offer is the short development time while exhibiting an efficiency comparable to imperative languages. This tutorial aims at presenting the principles and concepts underlying these languages and explaining them by examples. The objective of this paper is not to give a technical survey of the current state of art in research on CLP, but rather to give a tutorial introduction and to convey the basic philosophy that is behind the different ideas in CLP. It will discuss the currently most successful computation domains and provide an overview on the different consi...

... This paper reviews most of the work done by various groups along these lines and the current perspectives of our own research on Gamma. For the sake of clarity we separate the contributions in three categories: (1) the relevance of the chemical reaction model for software engineering, (2) extensions of the original model and (3) implementation issues.

In first approximation Core Facile is a simply typed -calculus enriched with parallel composition, dynamic channel generation, and input-output synchronous communication primitives. In this paper we explore the (dynamic) semantics of core Facile programs. This should be taken as a basis for the definition of abstract machines, the transformation of programs, and the development of modal specification languages. We claim two main contributions. We introduce a new semantics based on the notion of barbed bisimulation. We argue that the derived equivalence provides a more satisfying treatment of restriction, in particular by proving the adequacy of a natural translation of Facile into ß-calculus we suggest that our approach is in good harmony with previous research on the semantics of sub-calculi of Core Facile such as Chocs and ß-calculus. We illustrate at an abstract level various aspects of Facile compilation. In particular we introduce an `asynchronous' version of the Facile language...

In current constraint logic programming systems, constraint solving is hard-wired in a "black box". We are investigating the use of logic programs to define and implement constraint solvers 1 . The representation of constraint evaluation in the same formalism as the rest of the program greatly facilitates the prototyping, extension, specialization and combination of constraint solvers. In our approach, constraints are specified by definite clauses provided by a host language, while constraint evaluation is specified using multi-headed guarded clauses called constraint simplification rules (SiRs) 2 . SiRs define determinate conditional rewrite systems that express how conjunctions of constraints simplify. They have been used to encode a range of constraint solvers in our prototype implementation. Additionally, the definite clauses specifying a constraint can be evaluated in the host language, if the constraint is "callable" and no SiR can simplify it further. In this way our appr...

This report describes the PADDY partial deduction system. Its main features are that it can handle full Sepia, including advanced features; is automatic; always terminates; is provably correct on pure Prolog programs; uses a powerful adaptive transformation strategy; has fast transformation times; is based on an unfold/fold system.

Gamma was originally proposed in 1986 as a formalism for the definition of programs without artificial sequentiality. The basic idea underlying the formalism is to describe computation as a form of chemical reaction on a collection of individual pieces of data. Due to the very minimal nature of the language, and its absence of sequential bias, it has been possible to exploit this initial paradigm in various directions. This paper reviews most of the work done by various groups along these lines and the current perspectives of our own research on Gamma. For the sake of clarity we separate the contributions in three categories: (1) the relevance of the chemical reaction model for software engineering, (2) extensions of the original model and (3) implementation issues. Key-words: implicit parallelism, correctness proof, specification, program derivation, termination, abstract machine