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Proceedings of the Workshop on Membrane Computing, WMC 2016.
yesThis Workshop on Membrane Computing, at the Conference of Unconventional
Computation and Natural Computation (UCNC), 12th July 2016, Manchester,
UK, is the second event of this type after the Workshop at UCNC 2015 in
Auckland, New Zealand*. Following the tradition of the 2015 Workshop the
Proceedings are published as technical report.
The Workshop consisted of one invited talk and six contributed presentations
(three full papers and three extended abstracts) covering a broad spectrum of
topics in Membrane Computing, from computational and complexity theory to
formal verification, simulation and applications in robotics. All these papers â
see below, but the last extended abstract, are included in this volume.
The invited talk given by Rudolf Freund, âP SystemsWorking in Set Modesâ,
presented a general overview on basic topics in the theory of Membrane Computing
as well as new developments and future research directions in this area.
Radu Nicolescu in âDistributed and Parallel Dynamic Programming Algorithms
Modelled on cP Systemsâ presented an interesting dynamic programming
algorithm in a distributed and parallel setting based on P systems enriched with
adequate data structure and programming concepts representation. Omar Belingheri,
Antonio E. Porreca and Claudio Zandron showed in âP Systems with
Hybrid Setsâ that P systems with negative multiplicities of objects are less powerful
than Turing machines. Artiom Alhazov, Rudolf Freund and Sergiu Ivanov
presented in âExtended Spiking Neural P Systems with Statesâ new results regading
the newly introduced topic of spiking neural P systems where states are
considered.
âSelection Criteria for Statistical Model Checkerâ, by Mehmet E. Bakir and
Mike Stannett, presented some early experiments in selecting adequate statistical
model checkers for biological systems modelled with P systems. In âTowards
Agent-Based Simulation of Kernel P Systems using FLAME and FLAME GPUâ,
Raluca Lefticaru, Luis F. MacĂas-Ramos, IonuĆŁ M. Niculescu, LaurenĆŁiu MierlÄ
presented some of the advatages of implementing kernel P systems simulations in
FLAME. Andrei G. Florea and CÄtÄlin Buiu, in âAn Efficient Implementation and Integration of a P Colony Simulator for Swarm Robotics Applications" presented an interesting and efficient implementation based on P colonies for swarms of Kilobot robots.
*http://ucnc15.wordpress.fos.auckland.ac.nz/workshop-on-membrane-computingwmc-
at-the-conference-on-unconventional-computation-natural-computation
Towards Tractable Algebras for Bags
AbstractBags, i.e., sets with duplicates, are often used to implement relations in database systems. In this paper, we study the expressive power of algebras for manipulating bags. The algebra we present is a simple extension of the nested relation algebra. Our aim is to investigate how the use of bags in the language extends its expressive power and increases its complexity. We consider two main issues, namely (i) the impact of the depth of bag nesting on the expressive power and (ii) the complexity and the expressive power induced by the algebraic operations. We show that the bag algebra is more expressive than the nested relation algebra (at all levels of nesting), and that the difference may be subtle. We establish a hierarchy based on the structure of algebra expressions. This hierarchy is shown to be highly related to the properties of the powerset operator
Update Consistency for Wait-free Concurrent Objects
In large scale systems such as the Internet, replicating data is an essential
feature in order to provide availability and fault-tolerance. Attiya and Welch
proved that using strong consistency criteria such as atomicity is costly as
each operation may need an execution time linear with the latency of the
communication network. Weaker consistency criteria like causal consistency and
PRAM consistency do not ensure convergence. The different replicas are not
guaranteed to converge towards a unique state. Eventual consistency guarantees
that all replicas eventually converge when the participants stop updating.
However, it fails to fully specify the semantics of the operations on shared
objects and requires additional non-intuitive and error-prone distributed
specification techniques. This paper introduces and formalizes a new
consistency criterion, called update consistency, that requires the state of a
replicated object to be consistent with a linearization of all the updates. In
other words, whereas atomicity imposes a linearization of all of the
operations, this criterion imposes this only on updates. Consequently some read
operations may return out-dated values. Update consistency is stronger than
eventual consistency, so we can replace eventually consistent objects with
update consistent ones in any program. Finally, we prove that update
consistency is universal, in the sense that any object can be implemented under
this criterion in a distributed system where any number of nodes may crash.Comment: appears in International Parallel and Distributed Processing
Symposium, May 2015, Hyderabad, Indi
On the Expressive Power of Multiple Heads in CHR
Constraint Handling Rules (CHR) is a committed-choice declarative language
which has been originally designed for writing constraint solvers and which is
nowadays a general purpose language. CHR programs consist of multi-headed
guarded rules which allow to rewrite constraints into simpler ones until a
solved form is reached. Many empirical evidences suggest that multiple heads
augment the expressive power of the language, however no formal result in this
direction has been proved, so far.
In the first part of this paper we analyze the Turing completeness of CHR
with respect to the underneath constraint theory. We prove that if the
constraint theory is powerful enough then restricting to single head rules does
not affect the Turing completeness of the language. On the other hand,
differently from the case of the multi-headed language, the single head CHR
language is not Turing powerful when the underlying signature (for the
constraint theory) does not contain function symbols.
In the second part we prove that, no matter which constraint theory is
considered, under some reasonable assumptions it is not possible to encode the
CHR language (with multi-headed rules) into a single headed language while
preserving the semantics of the programs. We also show that, under some
stronger assumptions, considering an increasing number of atoms in the head of
a rule augments the expressive power of the language.
These results provide a formal proof for the claim that multiple heads
augment the expressive power of the CHR language.Comment: v.6 Minor changes, new formulation of definitions, changed some
details in the proof
Investigating Logics for Feasible Computation
The most celebrated open problem in theoretical computer science is, undoubtedly, the problem of whether P = NP. This is actually one instance of the many unresolved questions in the area of computational complexity. Many different classes of decision problems have been defined in terms of the resources needed to recognize them on various models of computation, such as deterministic or non-deterministic Turing machines, parallel machines and randomized machines. Most of the non-trivial questions concerning the inter-relationship between these classes remain unresolved. On the other hand, these classes have proved to be robustly defined, not only in that they are closed under natural transformations, but many different characterizations have independently defined the same classes. One such alternative approach is that of descriptive complexity, which seeks to define the complexity, not of computing a problem, but of describing it in a language such as the Predicate Calculus. It is particularly interesting that this approach yields a surprisingly close correspondence to computational complexity classes. This provides a natural characterization of many complexity classes that is not tied to a particular machine model of computation
Knowledge Representation Concepts for Automated SLA Management
Outsourcing of complex IT infrastructure to IT service providers has
increased substantially during the past years. IT service providers must be
able to fulfil their service-quality commitments based upon predefined Service
Level Agreements (SLAs) with the service customer. They need to manage, execute
and maintain thousands of SLAs for different customers and different types of
services, which needs new levels of flexibility and automation not available
with the current technology. The complexity of contractual logic in SLAs
requires new forms of knowledge representation to automatically draw inferences
and execute contractual agreements. A logic-based approach provides several
advantages including automated rule chaining allowing for compact knowledge
representation as well as flexibility to adapt to rapidly changing business
requirements. We suggest adequate logical formalisms for representation and
enforcement of SLA rules and describe a proof-of-concept implementation. The
article describes selected formalisms of the ContractLog KR and their adequacy
for automated SLA management and presents results of experiments to demonstrate
flexibility and scalability of the approach.Comment: Paschke, A. and Bichler, M.: Knowledge Representation Concepts for
Automated SLA Management, Int. Journal of Decision Support Systems (DSS),
submitted 19th March 200
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