Timed Soft Concurrent Constraint Programs: An Interleaved and a Parallel Approach

We propose a timed and soft extension of Concurrent Constraint Programming. The time extension is based on the hypothesis of bounded asynchrony: the computation takes a bounded period of time and is measured by a discrete global clock. Action prefixing is then considered as the syntactic marker which distinguishes a time instant from the next one. Supported by soft constraints instead of crisp ones, tell and ask agents are now equipped with a preference (or consistency) threshold which is used to determine their success or suspension. In the paper we provide a language to describe the agents behavior, together with its operational and denotational semantics, for which we also prove the compositionality and correctness properties. After presenting a semantics using maximal parallelism of actions, we also describe a version for their interleaving on a single processor (with maximal parallelism for time elapsing). Coordinating agents that need to take decisions both on preference values and time events may benefit from this language. To appear in Theory and Practice of Logic Programming (TPLP)

Process Algebras

Process Algebras are mathematically rigorous languages with well defined semantics that permit describing and verifying properties of concurrent communicating systems. They can be seen as models of processes, regarded as agents that act and interact continuously with other similar agents and with their common environment. The agents may be real-world objects (even people), or they may be artifacts, embodied perhaps in computer hardware or software systems. Many different approaches (operational, denotational, algebraic) are taken for describing the meaning of processes. However, the operational approach is the reference one. By relying on the so called Structural Operational Semantics (SOS), labelled transition systems are built and composed by using the different operators of the many different process algebras. Behavioral equivalences are used to abstract from unwanted details and identify those systems that react similarly to external experiments

Abstract Diagnosis for Timed Concurrent Constraint programs

The Timed Concurrent Constraint Language (tccp in short) is a concurrent logic language based on the simple but powerful concurrent constraint paradigm of Saraswat. In this paradigm, the notion of store-as-value is replaced by the notion of store-as-constraint, which introduces some differences w.r.t. other approaches to concurrency. In this paper, we provide a general framework for the debugging of tccp programs. To this end, we first present a new compact, bottom-up semantics for the language that is well suited for debugging and verification purposes in the context of reactive systems. We also provide an abstract semantics that allows us to effectively implement debugging algorithms based on abstract interpretation. Given a tccp program and a behavior specification, our debugging approach automatically detects whether the program satisfies the specification. This differs from other semiautomatic approaches to debugging and avoids the need to provide symptoms in advance. We show the efficacy of our approach by introducing two illustrative examples. We choose a specific abstract domain and show how we can detect that a program is erroneous.Comment: 16 page

An Interleaving Semantics of the Timed Concurrent Language for Argumentation to Model Debates and Dialogue Games

Time is a crucial factor in modelling dynamic behaviours of intelligent agents: activities have a determined temporal duration in a real-world environment, and previous actions influence agents' behaviour. In this paper, we propose a language for modelling concurrent interaction between agents that also allows the specification of temporal intervals in which particular actions occur. Such a language exploits a timed version of Abstract Argumentation Frameworks to realise a shared memory used by the agents to communicate and reason on the acceptability of their beliefs with respect to a given time interval. An interleaving model on a single processor is used for basic computation steps, with maximum parallelism for time elapsing. Following this approach, only one of the enabled agents is executed at each moment. To demonstrate the capabilities of language, we also show how it can be used to model interactions such as debates and dialogue games taking place between intelligent agents. Lastly, we present an implementation of the language that can be accessed via a web interface. Under consideration in Theory and Practice of Logic Programming (TPLP).Comment: Under consideration in Theory and Practice of Logic Programming (TPLP

Formal semantics for LIPS (Language for Implementing Parallel/distributed Systems)

This thesis presents operational semantics and an abstract machine for a point-to-point asynchronous message passing language called LIPS (Language for Implementing Parallel/ distributed Systems). One of the distinctive features of LIPS is its capability to handle computation and communication independently. Taking advantage of this capability, a two steps strategy has been adopted to define the operational semantics. The two steps are as follows: • A big-step semantics with single-step re-writes is used to relate the expressions and their evaluated results (computational part of LIPS). • The developed big-step semantics has been extended with Structural Operational Semantics (SOS) to describe the asynchronous message passing of LIPS (communication part of LIPS). The communication in LIPS has been implemented using Asynchronous Message Passing System (AMPS). It makes use of very simple data structures and avoids the use of buffers. While operational semantics is used to specify the meaning of programs, abstract machines are used to provide intermediate representation of the language's implementation. LIPS Abstract Machine (LAM) is defined to execute LIPS programs. The correctness of the execution of the LIPS program/expression written using the operational semantics is verified by comparing it with its equivalent code generated using the abstract machine. Specification of Asynchronous Communicating Systems (SACS) is a process algebra developed to specify the communication in LIPS programs. It is an asynchronous variant of Synchronous Calculus of Communicating Systems (SCCS). This research presents the SOS for SACS and looks at the bisimulation equivalence properties for SACS which can be used to verify the behaviour of a specified process. An implementation is said to be complete when it is equivalent to its specifications. SACS has been used for the high level specification of the communication part of LIPS programs and is implemented using AMPS. This research proves that SACS and AMPS are equivalent by defining a weak bisimulation equivalence relation between the SOS of both SACS and AMPS