Section: New Results
Concurrent Constraint Programming
Participants : Romain Beauxis, Moreno Falaschi, Catuscia Palamidessi, Carlos Olarte, Frank Valencia.
A smooth probabilistic extension of concurrent constraint programming
Concurrent constraint programming (ccp , [50] ) is a model of computation based on the notion of store as the information available for the process. Each process has access to a global store, with respect to which it tests and adds constraints. During the execution, the store can only increase. A domain-theoretic denotational semantics has been defined in [49] , that maps a process to the supremum store that it can reach. It is then possible to compute this supremum store by a fixed point construction, based on the grammar of the process.
Universal timed concurrent constraint programming
in his PhD thesis [13] , Olarte has studied a temporal concurrent constraint calculus as a model of concurrency for mobile, timed reactive systems. The study is conducted by developing a process calculus called utcc, Universal Temporal CCP. The thesis is that utcc is a model for concurrency where behavioral and declarative reasoning techniques coexist coherently, thus allowing for the specification and verification of mobile reactive systems in emergent application areas. The utcc calculus generalizes tcc with the ability to express mobility. Here mobility is understood as communication of private names as typically done for mobile systems and security protocols. The utcc calculus introduces parametric ask operations called abstractions that behave as persistent parametric asks during a time-interval but may disappear afterwards. The applicability of the calculus is shown in several domains of Computer Science. Namely, decidability of Pnueli's First-order Temporal Logic, closure-operator semantic characterization of security protocols, semantics of a Service-Oriented Computing language, and modeling of Dynamic Multimedia-Interaction systems.
Abstract interpretation
In [26] we have extended the semantics of constraint calculus tcc to a "collecting" semantics for the utcc calculus based on closure operators over sequences of constraints. Relying on this semantics, we have formalized the first general framework for data flow analyses of tcc and utcc programs by abstract interpretation techniques. The concrete and abstract semantics we have proposed are compositional, thus allowing us to reduce the complexity of data flow analyses. We have shown that our method is sound and parametric w.r.t. the abstract domain. Thus, different analyses can be performed by instantiating the framework. We have illustrated how it is possible to reuse abstract domains previously defined for logic programming, e.g., to perform a groundness analysis for tcc programs. We have shown the applicability of this analysis in the context of reactive systems. Furthermore, we have made also use of the abstract semantics to exhibit a secrecy flaw in a security protocol.
Declarative analysis of structured communications
In [28] we have described a unified concurrent-constraint framework for the declarative analysis of structured communications. By relying on the utcc constraint calculus, we have showed that in addition to the usual operational techniques from process calculi, the analysis of structured communications can elegantly exploit logic-based reasoning techniques. We have presented a concurrent constraint interpretation of the language for structured communications proposed by Honda, Vasconcelos, and Kubo [47] . Distinguishing features of our approach are: the possibility of including partial information (constraints) in the session model, the use of explicit time for reasoning about session duration and expiration, and a tight correspondence with logic, which formally relates session execution and linear-time temporal logic formulas.
Multimedia Interaction
In [29] we have argued for the utcc calculus as a declarative model for dynamic multimedia interaction systems. Firstly, we have shown that the notion of constraints as partial information allowed us to neatly define temporal relations between interactive agents or events. Secondly, we have shown that mobility in utcc allows for the specification of more flexible and expressive systems. Thirdly, by relying on the underlying temporal logic in utcc, we have shown how non-trivial temporal properties of the model can be verified. As an application we have proposed a model for dynamic interactive scores where interactive points can be defined to adapt the hierarchical structure of the score depending on the information inferred from the environment. Our model broadens the interaction mechanisms available for the composer in previous (more static) models.
Musical applications
In [30] we have illustrated that the constraint calculus ntcc is useful for modeling complex musical processes, in particular for music improvisation. For example, for the vertical dimension one can specify that a given process can nondeterministically choose any note satisfying a given constraint. For the horizontal dimension one can specify that the process can nondeterministically choose the time to play the note subject to a given time upper bound. This nondeterministic view is particularly suitable for processes representing a musician's choices when improvising. Similarly, the horizontal dimension may supply partial information on a rhythmic pattern that leaves room for variation while keeping a basic control. We have also illustrated how implementing a weaker ntcc model of a musical process may greatly simplify the formal verification of its properties. We have argued that this modeling strategy provides a "runnable specification" for music problems that eases the task of formally reasoning about them.
FORCES
In [22] we have provided an overview of of our associated-team FORCES focusing on its motivation, results and future research directions. FORCES (FORmalisms from Concurrency for Emergent Systems) is a Colombian-French project funded by the program of ÒEquipes AssociéesÓ of INRIA. The teams involved in this research collaboration are the Music Representation Research Group (IRCAM), AVISPA (Colciencias) and our team Comète. The main goal of the project is to provide more robust formalisms for analyzing the emergent systems our teams have been modeling during recent years: I.e., Security Protocols, Biological Systems and Multimedia Semantic Interaction. The results described in this sections were indeed obtained in the context of FORCES.
