A Distributed Algorithm for Adaptive Replication of Data

We present a distributed algorithm for replication of a data-item in a set of processors interconnected by a tree network. The algorithm is adaptive in the sense that the replication scheme of the item (i.e. the set of processors. each of which stores a replica of the data-item). changes as the read-write pattern of the processors in the network changes. The algorithm is optimal in the sense that when the replication scheme stabilizes, the total number of messages required for the reads and writes is minimal

The Communication Complexity of Atomic Commitment and of Gossiping

We consider the problem of atomic commitment of a transaction in a distributed database. This is a variant of the famous gossiping problem (see [HHL] for a survey). Given a set of communication costs between pairs of participant sites, we establish that the necessary communication cost for any atomic commitment algorithm is twice the cost of a certain minimum spanning tree. We also establish the necessary communication time for any atomic commitment algorithm, given a set of communication delays between pairs of participant sites, and the time at which each participant completes its subtransaction. Then we determine that both lower bounds are also upper bounds in the following sense. There is an efficient (i.e. polynomial-time) algorithm that, in the absence of failures, has a minimum communication cost. There is another efficient algorithm that, in the absence of failures, has a minimum communication time. However, unless P=NP, there is no efficient algorithm which has a minimum communication complexity, namely, for which the product of communication cost and communication time is minimum. Then we present a simple, linear time, distributed algorithm, called TREE-COMMIT, whose communication complexity is not worse than p times the minimum complexity, where p is the number of participants. Finally, we demonstrate that TREE-COMMIT is superior to the existing variants of the two-phase commit protocol

Adaptive search in mobile peer-to-peer databases

Information is stored in a plurality of mobile peers. The peers communicate in a peer to peer fashion, using a short-range wireless network. Occasionally, a peer initiates a search for information in the peer to peer network by issuing a query. Queries and pieces of information, called reports, are transmitted among peers that are within a transmission range. For each search additional peers are utilized, wherein these additional peers search and relay information on behalf of the originator of the search

The Multicast Policy and Its Relationship to Replicated Data Placement

In this paper we consider the communication complexity of maintaining the replicas of a logical data-item, in a database distributed over a computer network. We propose a new method, called the minimum spanning tree write, by which a processor in the network should multicast a write of a logical data-item, to all the processors that store replicas of the item. Then we show that the minimum spanning tree write is optimal from the communication cost point of view. We also demonstrate that the method by which a write is multicast to all the replicas of a data-item, affects the optimal replication scheme of the item, i.e., at which processors in the network the replicas should be located. Therefore, next we consider the problem of determining an optimal replication scheme for a data item, assuming that each processor employs the minimum spanning tree write at run-time. The problem for general networks is shown NP-Complete, but we provide efficient algorithms to obtain an optimal allocation scheme for three common types of network topologies. They are completely-connected, tree, and ring networks. For these topologies, efficient algorithms are also provided for the case in which reliability considerations dictate a minimum number of replicas

Decomposability and Its Role in Parallel Logic-Program Evaluation

This paper is concerned with the issue of parallel evaluation of logic programs. We define the concept of program decomposability, which means that the load of evaluation can be partitioned among a number of processors, without a need for communication among them. This in turn results in a very significant speed-up of the evaluation process. Some programs are decomposable, whereas others are not. We completely syntactically characterize three classes of single rule programs with respect to decomposability: nonrecursive, simple linear, and simple chain programs. We also establish two sufficient conditions for decomposability

Grand challenges for the spatial information community

The spatial information (SI) community has an opportunity to address major societal and scientific problems including public health, climate change, air pollution, transportation, and others. Beyond the significant contributions made by the SI community, more can be done by focusing the efforts of the community, and generalizing them. Focus can be achieved by an IMAGENET-like spatial information database and competition. Generalization can be achieved by solving spatio-temporal information problems in disciplines such as neuroscience, chemistry, biology, astronomy, and engineering

Why a Single Parallelization Strategy Is Not Enough in Knowledge Bases

We address the problem of parallelizing the evaluation of logic programs in data intensive applications. We argue that the appropriate parallelization strategy for logic-program evaluation depends on the program being evaluated. Therefore, this paper is concerned with the issues of program classification and parallelization strategies. We propose several parallelization strategies based on the concept of data reduction—the original logic program is evaluated by several processors working in parallel, each using only a subset of the database. The strategies differ on the evaluation cost, the overhead of communication and synchronization among processors, and the programs to which they are applicable. In particular, we start our study with pure parallelization, i.e., parallelization without overhead. An interesting class structure of logic programs is demonstrated, when considering amenability to pure parallelization. The relationship to the NC complexity class is demonstrated. Then we propose strategies that do incur an overhead, but are optimal in a sense that will be precisely defined. This paper makes the initial steps towards a theory of parallel logic programming

Active Databases for Communication Network Management

This paper has two purposes. First is to propose new database language-features for systems used in real-time management. These features enable the specification of change-traces, events and correlation among events, and they do so in a declarative set-oriented fashion. Second is to introduce network management as an important and interesting application of active distributed databases

10121 Abstracts Collection -- Computational Transportation Science

From 21.03. to 26.03.2010, the Dagstuhl Seminar 10121 ``Computational Transportation Science \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. 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