Results 1  10
of
43
The Logic of Typed Feature Structures
, 1992
"... Feature Structures and Path Congruences. The discussion of abstract feature structures raises a historical difficulty. While I do not dispute that the full theoretical investigation of feature structures modulo renaming is correctly attributed to Moshier, the idea of representing renaming classes b ..."
Abstract

Cited by 330 (3 self)
 Add to MetaCart
Feature Structures and Path Congruences. The discussion of abstract feature structures raises a historical difficulty. While I do not dispute that the full theoretical investigation of feature structures modulo renaming is correctly attributed to Moshier, the idea of representing renaming classes by equivalence relations over paths seems an obvious variant of the representation of such classes as deductively closed sets of path equations in Pereira and Shieber's account (1984) of the semantics of PATRII, which is further explored in Shieber's dissertation (1989).
Semantic foundations of concurrent constraint programming
, 1990
"... Concurrent constraint programming [Sar89,SR90] is a simple and powerful model of concurrent computation based on the notions of storeasconstraint and process as information transducer. The storeasvaluation conception of von Neumann computing is replaced by the notion that the store is a constr ..."
Abstract

Cited by 252 (26 self)
 Add to MetaCart
Concurrent constraint programming [Sar89,SR90] is a simple and powerful model of concurrent computation based on the notions of storeasconstraint and process as information transducer. The storeasvaluation conception of von Neumann computing is replaced by the notion that the store is a constraint (a finite representation of a possibly infinite set of valuations) which provides partial information about the possible values that variables can take. Instead of “reading” and “writing ” the values of variables, processes may now ask (check if a constraint is entailed by the store) and tell (augment the store with a new constraint). This is a very general paradigm which subsumes (among others) nondeterminate dataflow and the (concurrent) (constraint) logic programming languages. This paper develops the basic ideas involved in giving a coherent semantic account of these languages. Our first contribution is to give a simple and general formulation of the notion that a constraint system is a system of partial information (a la the information systems of Scott). Parameter passing and hiding is handled by borrowing ideas from the cylindric algebras of Henkin, Monk and Tarski to introduce diagonal elements and “cylindrification ” operations (which mimic the projection of information induced by existential quantifiers). The se;ond contribution is to introduce the notion of determinate concurrent constraint programming languages. The combinators treated are ask, tell, parallel composition, hiding and recursion. We present a simple model for this language based on the specificationoriented methodology of [OH86]. The crucial insight is to focus on observing the resting points of a process—those stores in which the process quiesces without producing more information. It turns out that for the determinate language, the set of resting points of a process completely characterizes its behavior on all inputs, since each process can be identified with a closure operator over the underlying constraint system. Very natural definitions of parallel composition, communication and hiding are given. For example, the parallel composition of two agents can be characterized by just the intersection of the sets of constraints associated with them. We also give a complete axiomatization of equality in this model, present
Timed Default Concurrent Constraint Programming
 Journal of Symbolic Computation
, 1996
"... Synchronous programming (Berry (1989)) is a powerful approach to programming reactive systems. Following the idea that "processes are relations extended over time" (Abramsky (1993)), we propose a simple but powerful model for timed, determinate computation, extending the closureoperator model for u ..."
Abstract

Cited by 61 (11 self)
 Add to MetaCart
Synchronous programming (Berry (1989)) is a powerful approach to programming reactive systems. Following the idea that "processes are relations extended over time" (Abramsky (1993)), we propose a simple but powerful model for timed, determinate computation, extending the closureoperator model for untimed concurrent constraint programming (CCP). In (Saraswat et al. 1994a) we had proposed a model for this called tcc here we extend the model of tcc to express strong timeouts: if an event A does not happen through time t, cause event B to happen at time t. Such constructs arise naturally in practice (e.g. in modeling transistors) and are supported in synchronous programming languages. The fundamental conceptual difficulty posed by these operations is that they are nonmonotonic. We provide a compositional semantics to the nonmonotonic version of concurrent constraint programming (Default cc) obtained by changing the underlying logic from intuitionistic logic to Reiter's default logic...
A Connection Based Approach to Commonsense Topological Description and Reasoning
, 1995
"... The standard mathematical approaches to topology, pointset topology and algebraic topology, treat points as the fundamental, undefined entities, and construct extended spaces as sets of points with additional structure imposed on them. Pointset topology in particular generalises the concept of ..."
Abstract

Cited by 49 (9 self)
 Add to MetaCart
The standard mathematical approaches to topology, pointset topology and algebraic topology, treat points as the fundamental, undefined entities, and construct extended spaces as sets of points with additional structure imposed on them. Pointset topology in particular generalises the concept of a `space' far beyond its intuitive meaning. Even algebraic topology, which concentrates on spaces built out of `cells' topologically equivalent to ndimensional discs, concerns itself chiefly with rather abstract reasoning concerning the association of algebraic structures with particular spaces, rather than the kind of topological reasoning which is required in everyday life, or which might illuminate the metaphorical use of topological concepts such as `connection' and `boundary'. This paper explores an alternative to these approaches, RCC theory, which takes extended spaces (`regions') rather than points as fundamental. A single relation, C (x; y) (read `Region x connects with reg...
The Concert System  Compiler and Runtime Support for Efficient, FineGrained Concurrent ObjectOriented Programs
, 1993
"... The introduction of concurrency complicates the already difficult task of largescale programming. Concurrent objectoriented languages provide a mechanism, encapsulation, for managing the increased complexity of largescale concurrent programs, thereby reducing the difficulty of large scale conc ..."
Abstract

Cited by 47 (12 self)
 Add to MetaCart
The introduction of concurrency complicates the already difficult task of largescale programming. Concurrent objectoriented languages provide a mechanism, encapsulation, for managing the increased complexity of largescale concurrent programs, thereby reducing the difficulty of large scale concurrent programming. In particular, finegrained objectoriented approaches provide modularity through encapsulation while exposing large degrees of concurrency. Though finegrained concurrent objectoriented languages are attractive from a programming perspective, they have historically suffered from poor efficiency. The goal of the Concert project is to develop portable, efficient implementations of finegrained concurrent objectoriented languages. Our approach incorporates careful program analysis and information management at every stage from the compiler to the runtime system. In this document, we outline the basic elements of the Concert approach. In particular, we discuss progr...
Interaction Abstract Machines
 Trends in ObjectBased Concurrent Computing
, 1993
"... Machines JeanMarc Andreoli, Paolo Ciancarini and Remo Pareschi European Computer Industry Research Centre Abstract In this paper, we introduce the metaphor of Interaction Abstract Machines (IAMs), in the same vein of such metaphors as the Chemical Abstract Machine. The main point about IAMs is ..."
Abstract

Cited by 45 (16 self)
 Add to MetaCart
Machines JeanMarc Andreoli, Paolo Ciancarini and Remo Pareschi European Computer Industry Research Centre Abstract In this paper, we introduce the metaphor of Interaction Abstract Machines (IAMs), in the same vein of such metaphors as the Chemical Abstract Machine. The main point about IAMs is in allowing interactions among independent, locally defined subsystems  a crucial requirement for capturing the global behavior of open systems. IAMs amalgamate dual concepts in distributed problem solving, such as blackboards and broadcast communication, which are exploited to account for, respectively, the tight integration and the loose integration of system components. The formal counterpart for the IAM metaphor can be found in the computational model of Linear Objects (LO), whose aim is the abstract modeling of concurrent agentoriented computations and whose operational semantics is given in terms of the proof theory of Linear Logic, a framework recently introduced to provide a theoretical account for the notion of (inter)action.
HigherOrder, Linear, Concurrent Constraint Programming
, 1992
"... We present a very simple and powerful framework for indeterminate, asynchronous, higherorder computation based on the formulaasagent and proofascomputation interpretation of (higherorder) linear logic [Gir87]. The framework significantly refines and extends the scope of the concurrent constrai ..."
Abstract

Cited by 30 (5 self)
 Add to MetaCart
We present a very simple and powerful framework for indeterminate, asynchronous, higherorder computation based on the formulaasagent and proofascomputation interpretation of (higherorder) linear logic [Gir87]. The framework significantly refines and extends the scope of the concurrent constraint programming paradigm [Sar89] in two fundamental ways: (1) by allowing for the consumption of information by agents it permits a direct modelling of (indeterminate) state change in a logical framework, and (2) by admitting simplytyped terms as dataobjects, it permits the construction, transmission and application of (abstractions of) programs at runtime. Much more dramatically, however, the framework can be seen as presenting higherorder (and if desired, constraintenriched) versions of a variety of other asynchronous concurrent systems, including the asynchronous ("input guarded") fragment of the (firstorder) ßcalculus, Hewitt's actors formalism, (abstract forms of) Gelernter's Lin...
Moded Flat GHC and Its MessageOriented Implementation Technique
, 1994
"... Concurrent processes can be used both for programming computation and for programming storage. Previous implementations of Flat GHC, however, have been tuned for computationintensive programs, and perform poorly for storageintensive programs (such as programs implementing reconfigurable data struc ..."
Abstract

Cited by 29 (10 self)
 Add to MetaCart
Concurrent processes can be used both for programming computation and for programming storage. Previous implementations of Flat GHC, however, have been tuned for computationintensive programs, and perform poorly for storageintensive programs (such as programs implementing reconfigurable data structures using processes and streams) and demanddriven programs. This paper proposes an optimization technique for programs in which processes are almost always suspended. The technique compiles unification for data transfer into message passing. Instead of reducing the number of process switching operations, the technique optimizes the cost of each process switching operation and reduces the number of cons operations for data buffering.
A Distributed Cooperating Constraints Solving System
 International Journal on Artificial Intelligence Tools
, 1995
"... . An appropriate combination of symbolic and numeric solvers often makes it possible to solve problems that none of these solvers can tackle alone. In this paper, we specify a cooperative architecture which allows using concurrently heterogeneous solvers when handling constraints over the reals. Thi ..."
Abstract

Cited by 29 (6 self)
 Add to MetaCart
. An appropriate combination of symbolic and numeric solvers often makes it possible to solve problems that none of these solvers can tackle alone. In this paper, we specify a cooperative architecture which allows using concurrently heterogeneous solvers when handling constraints over the reals. This architecture is based upon agents that communicate via asynchronous message passing. Agents are synchronized when a failure or a success occurs. Disjunctive constraints are handled by backtracking. Operational semantics and terminating conditions of such systems are discussed. Implementation issues are addressed. We end the presentation by several examples and give some computational results from a first prototype. 1 Introduction 1.1 Motivation Many industrial applications can be modeled by a set of constraints defined over the reals (e.g., financial applications, thermal flow problems, electromechanical engineering problems) . These systems of constraints are usually nonlinear or even...