37,053 research outputs found
Serializing the Parallelism in Parallel Communicating Pushdown Automata Systems
We consider parallel communicating pushdown automata systems (PCPA) and
define a property called known communication for it. We use this property to
prove that the power of a variant of PCPA, called returning centralized
parallel communicating pushdown automata (RCPCPA), is equivalent to that of
multi-head pushdown automata. The above result presents a new sub-class of
returning parallel communicating pushdown automata systems (RPCPA) called
simple-RPCPA and we show that it can be written as a finite intersection of
multi-head pushdown automata systems
On the Size Complexity of Non-Returning Context-Free PC Grammar Systems
Improving the previously known best bound, we show that any recursively
enumerable language can be generated with a non-returning parallel
communicating (PC) grammar system having six context-free components. We also
present a non-returning universal PC grammar system generating unary languages,
that is, a system where not only the number of components, but also the number
of productions and the number of nonterminals are limited by certain constants,
and these size parameters do not depend on the generated language
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
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
Partially-commutative context-free languages
The paper is about a class of languages that extends context-free languages
(CFL) and is stable under shuffle. Specifically, we investigate the class of
partially-commutative context-free languages (PCCFL), where non-terminal
symbols are commutative according to a binary independence relation, very much
like in trace theory. The class has been recently proposed as a robust class
subsuming CFL and commutative CFL. This paper surveys properties of PCCFL. We
identify a natural corresponding automaton model: stateless multi-pushdown
automata. We show stability of the class under natural operations, including
homomorphic images and shuffle. Finally, we relate expressiveness of PCCFL to
two other relevant classes: CFL extended with shuffle and trace-closures of
CFL. Among technical contributions of the paper are pumping lemmas, as an
elegant completion of known pumping properties of regular languages, CFL and
commutative CFL.Comment: In Proceedings EXPRESS/SOS 2012, arXiv:1208.244
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