9,285 research outputs found
Concurrent context-free grammars
In this paper we study some properties of context-free concurrent grammars which are controlled by Petri nets under parallel firing strategies, i.e., the transitions of a Petri net fire simultaneously in different modes. These variants of control increase the computational power of generative devices. Moreover, they can be used as theoretical models for parallel computing devices
Sublinear Parallel Time Recognition of Tree Adjoining Language
A parallel algorithm is presented for recognizing the class of languages generated by tree adjoining grammars, a tree rewriting system which has applications in computational Linguistics. This class of languages is known to properly include all context-free languages; for example, the non-context-free sets {anbncn} and {ww) are in this class. It is shown that the recognition problem for tree adjoining languages can be solved by a concurrent-read, exclusive-write parallel random-access machine (CREW PRAM) in 0 (log2(n)) time using polynomially many processors. This extends a previous result for context-free languages
Safety verification of asynchronous pushdown systems with shaped stacks
In this paper, we study the program-point reachability problem of concurrent
pushdown systems that communicate via unbounded and unordered message buffers.
Our goal is to relax the common restriction that messages can only be retrieved
by a pushdown process when its stack is empty. We use the notion of partially
commutative context-free grammars to describe a new class of asynchronously
communicating pushdown systems with a mild shape constraint on the stacks for
which the program-point coverability problem remains decidable. Stacks that fit
the shape constraint may reach arbitrary heights; further a process may execute
any communication action (be it process creation, message send or retrieval)
whether or not its stack is empty. This class extends previous computational
models studied in the context of asynchronous programs, and enables the safety
verification of a large class of message passing programs
Message-Passing Protocols for Real-World Parsing -- An Object-Oriented Model and its Preliminary Evaluation
We argue for a performance-based design of natural language grammars and
their associated parsers in order to meet the constraints imposed by real-world
NLP. Our approach incorporates declarative and procedural knowledge about
language and language use within an object-oriented specification framework. We
discuss several message-passing protocols for parsing and provide reasons for
sacrificing completeness of the parse in favor of efficiency based on a
preliminary empirical evaluation.Comment: 12 pages, uses epsfig.st
On Series-Parallel Pomset Languages: Rationality, Context-Freeness and Automata
Concurrent Kleene Algebra (CKA) is a formalism to study concurrent programs.
Like previous Kleene Algebra extensions, developing a correspondence between
denotational and operational perspectives is important, for both foundations
and applications. This paper takes an important step towards such a
correspondence, by precisely relating bi-Kleene Algebra (BKA), a fragment of
CKA, to a novel type of automata, pomset automata (PAs). We show that PAs can
implement the BKA semantics of series-parallel rational expressions, and that a
class of PAs can be translated back to these expressions. We also characterise
the behavior of general PAs in terms of context-free pomset grammars;
consequently, universality, equivalence and series-parallel rationality of
general PAs are undecidable.Comment: Accepted manuscrip
Parallel on-line parsing in constant time per word
An on-line parser processes each word as soon as it is typed by the user, without waiting for the end of the sentence. Thus, in an interactive system, a sentence will be parsed almost immediately after the last word has been presented.\ud
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The complexity of an on-line parser is determined by the resources needed for the analysis of a single word, as it is assumed that previous words have been processed already. Sequential parsing algorithms like CYK or Earley need O(n2) time for the nth word. A parallel implementation in O(n) time on O(n) processors is straightforward. In this paper a novel parallel on-line parser is presented that needs O(1) time on O(n2) processors
Concurrent Lexicalized Dependency Parsing: The ParseTalk Model
A grammar model for concurrent, object-oriented natural language parsing is
introduced. Complete lexical distribution of grammatical knowledge is achieved
building upon the head-oriented notions of valency and dependency, while
inheritance mechanisms are used to capture lexical generalizations. The
underlying concurrent computation model relies upon the actor paradigm. We
consider message passing protocols for establishing dependency relations and
ambiguity handling.Comment: 90kB, 7pages Postscrip
Constraint Design Rewriting
We propose an algebraic approach to the design and transformation of constraint networks, inspired by Architectural Design Rewriting. The approach can be understood as (i) an extension of ADR with constraints, and (ii) an application of ADR to the design of reconfigurable constraint networks. The main idea is to consider classes of constraint networks as algebras whose operators are used to denote constraint networks with terms. Constraint network transformations such as constraint propagations are specified with rewrite rules exploiting the network’s structure provided by terms
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