Chapter 2: Executive summaryThe CONFER-2 Working Group is a framework to keep together the
community of the previous Basic Research Action CONFER, and to provide
two annual workshops. The objective of CONFER-2 is to create both the
theoretical foundations and the technology for combining the expressive
power of the functional and the concurrent computational models. The
action is organized around four main areas :
In the area of Foundational Models and Abstract Machines, the research
activity has progressed in three main areas.
Foundational Models and Abstract Machines
- Logics for Concurrency and the l-calculus
- Programming Languages
Firstly a book by Asperti and Guerrini has been published at Cambride
University Press. It summarizes the research on Optimal Reductions in
the lambda calculus. This area has been very active in the last
decade, especially inside our Working Group (see previous Progress
Reports of CONFER and CONFER-2). In the same spirit, the study of
origin tracking in the lambda calculus has been pursued by Klop at
Secondly, a result on the finiteness of the normalization cone in the
lambda-sigma calculus has been published by Melliès on leave from
University of Edinburgh to ENS. In the same spirit, Bruni, Gadduci, and
Montanari have studied the connection between three reduction systems:
rewriting logic (Meseguer), action calculi (Milner), and tile logic
(Montanari). Both approaches are based on category theory.
Thirdly, the work on Action Calculi is still strongly developed at
Cambridge. Action Calculi form an abstract model for calculi with
bound variables and guards (preventing from computing below
them). Leifer investigates general methods for deriving labeled
transition systems from reduction rules in a way initiated by Milner
and Sewell. Indeed labeled transition systems provide an intensional
semantics describing the interactions of processes on contexts, and it
would be useful to automatically derive bisimulations as congruences
from the extensional semantics given in terms of reduction rules and
observational equivalences. A correspondence between action calculus
and the synchronous pi-calculus has been also studied by Gardner.
In the area of Calculi, progress has been made mainly in four
Security, which is a major issue for distributed languages with mobile
primitives, has been studied in various forms at different sites
inside CONFER-2. Secure encapsulation is proposed by Sewell and Vitek
as a way of assembling concurrent, software systems with untrusted or
partially untrusted parts. Principals have been added to the join
calculus by Abadi, Fournet and Gonthier. It allows formal statements
about authentication and secrecy, which may be proved with standard
proof techniques of process calculi. Another proof technique has been
developed by Amadio and Prasad for the verification of secrecy and
authentication with symmetric shared keys. Hennessy and Yoshida
consider types as a way of expressing locality in the pi-calculus.
Finally, a dependency calculus is studied by Conchon and Pottier for
descriptions of static interference properties using data flow
The theory of asynchronous bisimulations equivalences has been
intensively considered. A tutorial on asynchronous calculi has been
published by Sangiorgi. The work on the connection between the
synchronous and asynchronous pi-calculi is pursued by Quaglia and
Walker through typed barbed equivalences. Merro gives a labeled
characterization of barbed-congruences in the asynchronous pi-calculus
without matching. Castellani and Hennessy have investigated an
asynchronous version of CCS with both may and must testing preorders,
as a basis for future work on the theory of testing for the
Various localized asynchronous calculi have also been introduced or
examined during last year. The receptive asynchronous distributed
pi-calculus of Amadio, Boudol and Loussaine is based on a typing
discipline insuring uniform receptiveness. Its expressivity is shown
through the coding of standard examples. Safe Ambients is a new theory
of Levi and Sangiorgi which provides a nice equational theory for
Ambients. The feasibility of a distributed implementation for Ambients
has been explored by Fournet, Lévy and Schmitt.
The pi-calculus may also have a symmetric expression through the
Parrow and Victor's fusion calculus. Its expressivity is studied by
Laneve and Victor. Gardner also shows the connection with action
The theory of concurrent objects is another important direction of the
Calculi area. The aliasing model of Obliq, Ojeblik, demonstrates that
several different interpretations exist for the initial Cardelli's
Obliq calculus. The objective join calculus is still under development
by Fournet, Laneve, Maranget and Rémy. The extension of the
pi-calculus with concurrent objects has been published in a journal by
Liu and Walker. Finally, Dal Zilio achieved his PhD on the theory of
types for objects by using the Boudol's Blue Calculus.
Several more ponctual results may also be mentioned under the Calculi
area: Sangiorgi studies CIA (Concurrent Idealised Algol),
History-Dependent Automata is a framework for model checking for
the finite pi-calculus.
In the area of Logics for Concurrency and the l-calculus,
the work has been concentrated this year mainly at ENS and Edinburgh.
Concurrent Games semantics is a new setting introduced by Abramsky and
Melliès. Its completeness with respect to the multiplicative
additive linear logic has been proved. Danos et al. have connected
concurrent games theory with the Ehrhard hypercoherent space model.
The duality of call-by-name and call-by-value on one hand, and of
input and output on the other hand, is explored by Curien and Herbelin
via the Curry-Howard correspondence with the fragments LKT/LKQ of the
linear logic. The fragment LKTQ is also considered by Danos. This work
surprisingly provides a symmetric and dual lambda-calculus.
Finally, in the area of Programming Languages, progress has been
produced in the following directions.
Nomadic Pict is a distributed version of Pierce/Turner's Pict
language. Sewell, Unyapoth and Wojciechowski continues their work on
the design and semantics. The implementation is now completed. Jocaml
(Caml augmented with the join-calculus primitives) has been equipped of
a distributed garbage collector (as published in previous Progress
Report). At Pisa, Klaim (Kernel Language for Agents Interaction and
Mobility) is a prototype language for coordinating processes which run
on a net.
ICL explores the downstream use of agent technology with Fujitsu
Laboratories, and ICL Businesses. The usage of Facile has been pushed
to the Java community by the new availability of MLj (Standard ML
compiled to Java) of Microsoft Research. As Facile is written in SML,
one easily get the translation of Facile programs to JVM code, and to
strengthen the compatibility with other Java programs.
During Year 2 of CONFER-2 two workshops have been held.
The working group has produced about 65 reports and several of these
have been published at conferences, international workshops and
journals. Many of these works were produced by researchers at
different sites within the Working Group and can be stated as
state-of-the-art research. They are mainly accessible at URL
where a Web page on Mobility is maintained by Uwe Nestmann,
who moved in September 1997 from INRIA Rocquencourt to Aalborg.
Several Ph.D.'s are in preparation in the action, and several have
This report can be accessed on the World Wide Web at: