On the Expressiveness of Spatial Constraint Systems

In this paper we shall report on our progress using spatial constraint system as an abstract representation of modal and epistemic behaviour. First we shall give an introduction as well as the background to our work. Then, we present our preliminary results on the representation of modal behaviour by using spatial constraint systems. Then, we present our ongoing work on the characterization of the epistemic notion of knowledge. Finally, we discuss about the future work of our research

Recursion vs Replication in Process Calculi: Expressiveness

International audienceIn this paper we shall survey and discuss in detail the work on the relative expressiveness of recursion and replication in various process calculi. Namely, CCS, the pi-calculus, and the Ambient calculus. We shall give evidence that the ability of expressing recursive behaviour via replication often depends on the scoping mechanisms of the given calculus which compensate for the restriction of replication

Opinions and Beliefs as constraint system operators

Appears as Abstract Paper at the Technical Communications of the 31st International Conference on Logic Programming (ICLP 2015)International audienceThe growing presence of digital distributed systems in social life is exemplified by many particular instances, including opinion forums, social networks, dating sites and photo sharing portals. The increased usage in the last decade of these systems brings various risks and behaviors, inherent from the social interaction therein. An epistemic aspect is singled out as a common feature shared between these systems and the behaviors carried within them. Designing, constructing and verifying formalisms to represent information that is epistemic in nature can help develop a sound theory to analyze the scenarios mentioned before and at the same time bridge the concepts involved to a logical and mathematical domain. Regarding this, a specific concept of declarative and logic programming, that of a constraint system, deals with information represented by constraints (a constraint c could be a logical proposition partially describing a bigger system, e.g. temperature > 20). Constraint systems capable of incorporating the concept of spatiality such as user-spaces or message walls already exist (i.e. [c]_i , could read as " data/belief/constraint c belongs to agent i "). However, the movement of information between spaces is still not designed nor included in said constraint systems. Some process algebras do possess a concept of space mobility, notwithstanding, it is from an operational point of view, specifying only its behavior. Therefore it remains to mathematically define it along with all its properties. The proposed project intends to provide constraint systems with an algebraic operator that correspond to moving information in-between spaces as to mimic the mobility of data of distributed systems such as posting opinions/lies to other spaces or publicly disclosing data (i.e. ↑_i c reads as " extruding data/belief/constraint c from the space of agent i). Also, this extrusion operator should have a direct relationship with the spatiality operator, meaning that it should be modeled in constraint systems that also posses the concept of space (i.e. [c u ↑_i d] i = [c]_i u d reads " information d is extruded from the space of agent i " , it can be alternatively interpreted as agent i posting an opinion d). The authors developed a constraint system implementing the concepts of space and extrusion. The interaction between these conceptos account for mobility with no side effects , it is modeled as extrusion being the right inverse of space (i.e. [↑_i c]_i = c for any agent i). Additionally, given an already defined concept of space in a constraint system, the authors described different constructive ways of defining its extrusion and their mathematical properties. As a practical example, by means of a constraint system with space and extrusion, the authors gave semantic meaning to a logic with modalities of belief Bi and utterance Ui where BiUiφ ⇔ φ for any formula φ of the logic

Universal Concurrent Constraint Programing: Symbolic Semantics and Applications to Security

International audienceWe introduce the Universal Timed Concurrent Constraint Programming (utcc) process calculus; a generalisation of Timed Concurrent Constraint Programming. The utcc calculus allows for the specification of mobile behaviours in the sense of Milner's pi-calculus: Generation and communication of private channels or links. We first endow utcc with an operational semantics and then with a symbolic semantics to deal with problematic operational aspects involving infinitely many substitutions and divergent internal computations. The novelty of the symbolic semantics is to use temporal constraints to represent finitely infinitely-many substitutions. We also show that utcc has a strong connection with Pnueli's Temporal Logic. This connection can be used to prove reachability properties of utcc processes. As a compelling example, we use utcc to exhibit the secrecy flaw of the Needham-Schroeder security protocol

Universal Timed Concurrent Constraint Programming

International audienceIn this doctoral work we aim at developing a rich timed con- current constraint (tcc) based language with strong ties to logic. The new calculus called Universal Timed Concurrent Constraint (utcc) increases the expressiveness of tcc languages allowing infinite behaviour and mobility. We introduce a constructor of the form (abs x; c)P (Abstraction in P) that can be viewed as a dual operator of the hidden operator local x in P. i.e. the later can be viewed as an existential quantification on the variable x and the former as an universal quantification of x, executing P[t=x] for all t s.t. the current store entails c[t=x]. As a compelling application, we applied this calculus to verify security protocols

Concurrent Constraint Calculi: a Declarative Paradigm for Modeling Music Systems.

Concurrent constraint programming (CCP) has emerged as a simple but powerful paradigm for concurrent systems; i.e. systems of multiple agents that interact with each other as for example in a collection of music processes (musicians) performing a particular piece. The ntcc calculus is a CCP formalism for modeling temporal reactive systems. In ntcc, processes can be constrained by temporal requirements such as delays, time-outs and pre-emptions. Thus, the calculus integrates two dimensions of computation: a horizontal dimension dealing with partial information (e.g., note > 60) and a vertical one in which temporal requirements come into play (e.g., a process must be executed at any time within the next ten time units). We shall show that the above integration is remarkably 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 shall also illustrate how implementing a weaker ntcc model of a musical process may greatly simplify the formal verification of its properties. We argue that this modeling strategy provides a "runnable specification" for music problems that eases the task of formally reasoning about them

Linearity, Persistence and Testing Semantics in the Asynchronous Pi-Calculus

International audienceIn [CSVV06] the authors studied the expressiveness of persistence in the asynchronous pi calculus (Api) wrt weak barbed congruence. The study is incomplete because it ignores the issue of divergence. In this paper we present an expressiveness study of persistence in the asynchronous pi-calculus (Api) wrt DeNicola and Hennesy's testing scenario which is sensitive to divergence. We consider Api and theree sub-languages of it, each capturing one source of persistence: the persistent-input calculus (PIApi), the persistent-output calculus (POApi) and persistent calculus (PApi). In [CSVV06] the authors showed encodings from Api into semipersistent calculi are correct wrt weak barbed congruence. In this paper we prove that, under some general conditions, there cannot be an encoding from Api into a (semi)-persistent calculus preserving the must testing semantics. [CSVV06 ] C. Palamidessi, V. Saraswat, F. Valencia and B. Victor. On the Expressiveness of Linearity vs Persistence in the Asynchronous Pi Calculus. LICS 2006:59-68,2006

Modeling Cellular Signaling Systems: An Abstraction-Refinement Approach

International audienceThe molecular mechanisms of cell communication with the environment involve many concurrent processes governing dynamically the cell function. This concurrent behavior makes traditional methods, such as differential equations, unsatisfactory as a modeling strategy since they do not scale well when a more detailed view of the system is required. Concurrent Constraint Programming (CCP) is a declarative model of concurrency closely related to logic for specifying reactive systems, i.e., systems that continuously react with the environment. Agents in CCP interact by telling and asking information represented as constraints (e.g., x > 42). In this paper we describe a modeling strategy for cellular signaling systems based on a temporal and probabilistic extension of CCP. Starting from an abstract model, we build refinements adding further details coming from experimentation or abstract assumptions. The advantages of our approach are: due to the notion of partial information as constraints in CCP, the model can be straightforwardly extended when more information is available; qualitative and quantitative information can be represented by means of probabilistic constructs of the language; finally, the model is a runnable specification and can be executed, thus allowing for the simulation of the system. We outline the use of this methodology to model the interaction of G-protein-coupled receptors with their respective G-proteins that activates signaling pathways inside the cell. We also present simulation results obtained from an implementation of the framewor

An Algebraic View of Space/Belief and Extrusion/Utterance for Concurrency/Epistemic Logic

International audienceWe enrich spatial constraint systems with operators to specify information and processes moving from a space to another. We shall refer to these news structures as spatial constraint systems with extrusion. We shall investigate the properties of this new family of constraint systems and illustrate their applications. From a computational point of view the new operators provide for pro-cess/information extrusion, a central concept in formalisms for mobile communication. From an epistemic point of view extrusion corresponds to a notion we shall call utterance; a piece of information that an agent communicates to others but that may be inconsistent with the agent's beliefs. Utterances can then be used to express instances of epistemic notions, which are common place in social media, such as hoaxes or intentional lies. Spatial constraint systems with extrusion can be seen as complete Heyting algebras equipped with maps to account for spatial and epistemic specification