2,162 research outputs found
Dependability in Aggregation by Averaging
Aggregation is an important building block of modern distributed
applications, allowing the determination of meaningful properties (e.g. network
size, total storage capacity, average load, majorities, etc.) that are used to
direct the execution of the system. However, the majority of the existing
aggregation algorithms exhibit relevant dependability issues, when prospecting
their use in real application environments. In this paper, we reveal some
dependability issues of aggregation algorithms based on iterative averaging
techniques, giving some directions to solve them. This class of algorithms is
considered robust (when compared to common tree-based approaches), being
independent from the used routing topology and providing an aggregation result
at all nodes. However, their robustness is strongly challenged and their
correctness often compromised, when changing the assumptions of their working
environment to more realistic ones. The correctness of this class of algorithms
relies on the maintenance of a fundamental invariant, commonly designated as
"mass conservation". We will argue that this main invariant is often broken in
practical settings, and that additional mechanisms and modifications are
required to maintain it, incurring in some degradation of the algorithms
performance. In particular, we discuss the behavior of three representative
algorithms Push-Sum Protocol, Push-Pull Gossip protocol and Distributed Random
Grouping under asynchronous and faulty (with message loss and node crashes)
environments. More specifically, we propose and evaluate two new versions of
the Push-Pull Gossip protocol, which solve its message interleaving problem
(evidenced even in a synchronous operation mode).Comment: 14 pages. Presented in Inforum 200
From service-oriented architecture to service-oriented enterprise
Service-Oriented Architecture (SOA) was originally motivated by enterprise demands for better business-technology alignment and higher flexibility and reuse. SOA evolved from an initial set of ideas and principles to Web services (WS) standards now widely accepted by industry. The next phase of SOA development is concerned with a scalable, reliable and secure infrastructure based on these standards, and guidelines, methods and techniques for developing and maintaining service delivery in dynamic enterprise settings. In this paper we discuss the principles and main elements of SOA. We then present an overview of WS standards. And finally we come back to the original motivation for SOA, and how these can be realized
Computational Complexity of Atomic Chemical Reaction Networks
Informally, a chemical reaction network is "atomic" if each reaction may be
interpreted as the rearrangement of indivisible units of matter. There are
several reasonable definitions formalizing this idea. We investigate the
computational complexity of deciding whether a given network is atomic
according to each of these definitions.
Our first definition, primitive atomic, which requires each reaction to
preserve the total number of atoms, is to shown to be equivalent to mass
conservation. Since it is known that it can be decided in polynomial time
whether a given chemical reaction network is mass-conserving, the equivalence
gives an efficient algorithm to decide primitive atomicity.
Another definition, subset atomic, further requires that all atoms are
species. We show that deciding whether a given network is subset atomic is in
, and the problem "is a network subset atomic with respect to a
given atom set" is strongly -.
A third definition, reachably atomic, studied by Adleman, Gopalkrishnan et
al., further requires that each species has a sequence of reactions splitting
it into its constituent atoms. We show that there is a to decide whether a given network is reachably atomic, improving
upon the result of Adleman et al. that the problem is . We
show that the reachability problem for reachably atomic networks is
-.
Finally, we demonstrate equivalence relationships between our definitions and
some special cases of another existing definition of atomicity due to Gnacadja
06121 Abstracts Collection -- Atomicity: A Unifying Concept in Computer Science
From 19.03.06 to 24.03.06, the Dagstuhl Seminar 06121 ``Atomicity: A Unifying Concept in Computer Science\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
The Atomic Manifesto: a Story in Four Quarks
This report summarizes the viewpoints and insights gathered in the Dagstuhl Seminar on Atomicity in System Design and Execution, which was attended by 32 people from four different scientific communities: database and transaction processing systems, fault tolerance and dependable systems, formal methods for system design and correctness reasoning, and hardware architecture and programming languages. Each community presents its position in interpreting the notion of atomicity and the existing state of the art, and each community identifies scientific challenges that should be addressed in future work. In addition, the report discusses common themes across communities and strategic research problems that require multiple communities to team up for a viable solution.
The general theme of how to specify, implement, compose, and reason about extended
and relaxed notions of atomicity is viewed as a key piece in coping with
the pressing issue of building and maintaining highly dependable systems that
comprise many components with complex interaction patterns
Transaction Management Model for Mobile Database
Transaction support is crucial in mobile data management. Specific characteristics of
mobile environments (e.g. variable bandwidth, disconnections, and limited resources on
mobile hosts) make traditional transaction management techniques no longer
appropriate. This is due the fact that the Atomicity, Consistency, Isolation and Durability
(ACID) properties of transactions are not simply followed, in particular the consistency
property. Thus, transaction management models adopting weaker form of consistency
are needed and these models can now tolerate a limited amount of consistency. As a
result, several transaction management models for mobile databases have been
proposed, each of which has attempted to overcome some issues pertaining to
transaction processing in mobile environment. However, issues such as
(a) only one mobile host (MH) is allowed to update the data item
(b) large number of rejected transactions
(c) commit time execution of transactions at mobile host (MH) is large
are not well handled.
The proposed the model with the aims at solving the stated issues. The main idea
underlying the model is that transaction execution can be done at the base station (BS)
and mobile host (MHs). Transactions at a MH can update data locally and then precommit.
When the MH connects to the BS, these pre-committed transactions are sent to
the BS and re-executed as base transactions (BT) to maintain data consistency at the BS.
BTs are serialized on the master data stored at the BS. This will results in data
consistency.
The availability of data item at MHs makes the execution of transaction at MHs
possible. Each MH is allocated some value of data item, and the rest of it is kept at the
base server. By having the own this resource, a transaction at a MH is allowed to update
the data item within the limit of iSi. The model has been implemented and the result has
shown that the model works correctly as expected
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