A formal perspective on the view selection problem

The view selection problem is to choose a set of views to materialize over a database schema, such that the cost of evaluating a set of workload queries is minimized and such that the views fit into a prespecified storage constraint. The two main applications of the view selection problem are materializing views in a database to speed up query processing, and selecting views to materialize in a data warehouse to answer decision support queries. In addition, view selection is a core problem for intelligent data placement over a wide-area network for data integration applications and data management for ubiquitous computing. We describe several fundamental results concerning the view selection problem. We consider the problem for views and workloads that consist of equality-selection, project and join queries, and show that the complexity of the problem depends crucially on the quality of the estimates that a query optimizer has on the size of the views it is considering to materialize. When a query optimizer has good estimates of the sizes of the views, we show a somewhat surprising result, namely, that an optimal choice of views may involve a number of views that is exponential in the size of the database schema. On the other hand, when an optimizer uses standard estimation heuristics, we show that the number of necessary views and the expression size of each view are polynomially bounded. Received: November 20, 1001 / Accepted: May 30, 2002 / Published online: September 25, 2002     

Cloning and analysis of CoEXG1, a secreted 1,3-beta-glucanase of the yeast biocontrol agent Candida oleophila

Lytic enzymes may have a role in the biological control of fungi. The yeast biocontrol agent, Candida oleophila, is an excellent subject to research this matter. In the present study, CoEXG1, which encodes for a secreted 1,3-beta-glucanase, is the first gene to be cloned from C. oleophila. It was isolated from a partial genomic library and analysed. Its open reading frame and putative promoter were expressed in baker's yeast, Saccharomyces cerevisiae. The reading frame, expressed under the inducible GAL1 promoter, caused an increased secretion of beta-glucanase, and the putative promoter region activated the lacZ reporter gene, to which it was fused. Sequencing analysis revealed that CoEXG1 carries the signature pattern of the 5 glycohydrolases family and has a putative secretion leader, as well as a high degree of identity to yeast 1,3-beta-glucanases. The GenBank Accession No. of CoEXG1 is AF393806.     

Solving coalitional resource games

Coalitional Resource Games (crgs) are a form of Non-Transferable Utility (ntu) game, which provide a natural formal framework for modelling scenarios in which agents must pool scarce resources in order to achieve mutually satisfying sets of goals. Although a number of computational questions surrounding crgs have been studied, there has to date been no attempt to develop solution concepts for crgs, or techniques for constructing solutions. In this paper, we rectify this omission. Following a review of the crg framework and a discussion of related work, we formalise notions of coalition structures and the core for crgs, and investigate the complexity of questions such as determining nonemptiness of the core. We show that, while such questions are in general computationally hard, it is possible to check the stability of a coalition structure in time exponential in the number of goals in the system, but polynomial in the number of agents and resources. As a consequence, checking stability is feasible for systems with small or bounded numbers of goals. We then consider constructive approaches to generating coalition structures. We present a negotiation protocol for crgs, give an associated negotiation strategy, and prove that this strategy forms a subgame perfect equilibrium. We then show that coalition structures produced by the protocol satisfy several desirable properties: Pareto optimality, dummy player, and pseudo-symmetry.     

Beeping a maximal independent set

We consider the problem of computing a maximal independent set (MIS) in an extremely harsh broadcast model that relies only on carrier sensing. The model consists of an anonymous broadcast network in which nodes have no knowledge about the topology of the network or even an upper bound on its size. Furthermore, it is assumed that an adversary chooses at which time slot each node wakes up. At each time slot a node can either beep, that is, emit a signal, or be silent. At a particular time slot, beeping nodes receive no feedback, while silent nodes can only differentiate between none of its neighbors beeping, or at least one of its neighbors beeping. We start by proving a lower bound that shows that in this model, it is not possible to locally converge to an MIS in sub-polynomial time. We then study four different relaxations of the model which allow us to circumvent the lower bound and find an MIS in polylogarithmic time. First, we show that if a polynomial upper bound on the network size is known, it is possible to find an MIS in $\mathcal O (\log ^3 n)$ time. Second, if we assume sleeping nodes are awoken by neighboring beeps, then we can also find an MIS in $\mathcal O (\log ^3 n)$ time. Third, if in addition to this wakeup assumption we allow sender-side collision detection, that is, beeping nodes can distinguish whether at least one neighboring node is beeping concurrently or not, we can find an MIS in $\mathcal O (\log ^2 n)$ time. Finally, if instead we endow nodes with synchronous clocks, it is also possible to find an MIS in $\mathcal O (\log ^2 n)$ time.     

Language resources for Hebrew

We describe a suite of standards, resources and tools for computational encoding and processing of Modern Hebrew texts. These include an array of XML schemas for representing linguistic resources; a variety of text corpora, raw, automatically processed and manually annotated; lexical databases, including a broad-coverage monolingual lexicon, a bilingual dictionary and a WordNet; and morphological processors which can analyze, generate and disambiguate Hebrew word forms. The resources are developed under centralized supervision, so that they are compatible with each other. They are freely available and many of them have already been used for several applications, both academic and industrial.

Data integration with uncertainty

This paper reports our first set of results on managing uncertainty in data integration. We posit that data-integration systems need to handle uncertainty at three levels and do so in a principled fashion. First, the semantic mappings between the data sources and the mediated schema may be approximate because there may be too many of them to be created and maintained or because in some domains (e.g., bioinformatics) it is not clear what the mappings should be. Second, the data from the sources may be extracted using information extraction techniques and so may yield erroneous data. Third, queries to the system may be posed with keywords rather than in a structured form. As a first step to building such a system, we introduce the concept of probabilistic schema mappings and analyze their formal foundations. We show that there are two possible semantics for such mappings: by-table semantics assumes that there exists a correct mapping but we do not know what it is; by-tuple semantics assumes that the correct mapping may depend on the particular tuple in the source data. We present the query complexity and algorithms for answering queries in the presence of probabilistic schema mappings, and we describe an algorithm for efficiently computing the top-k answers to queries in such a setting. Finally, we consider using probabilistic mappings in the scenario of data exchange.     

Representing uncertain data: models, properties, and algorithms

In general terms, an uncertain relation encodes a set of possible certain relations. There are many ways to represent uncertainty, ranging from alternative values for attributes to rich constraint languages. Among the possible models for uncertain data, there is a tension between simple and intuitive models, which tend to be incomplete, and complete models, which tend to be nonintuitive and more complex than necessary for many applications. We present a space of models for representing uncertain data based on a variety of uncertainty constructs and tuple-existence constraints. We explore a number of properties and results for these models. We study completeness of the models, as well as closure under relational operations, and we give results relating closure and completeness. We then examine whether different models guarantee unique representations of uncertain data, and for those models that do not, we provide complexity results and algorithms for testing equivalence of representations. The next problem we consider is that of minimizing the size of representation of models, showing that minimizing the number of tuples also minimizes the size of constraints. We show that minimization is intractable in general and study the more restricted problem of maintaining minimality incrementally when performing operations. Finally, we present several results on the problem of approximating uncertain data in an insufficiently expressive model.     

MiniCon: A scalable algorithm for answering queries using views

The problem of answering queries using views is to find efficient methods of answering a query using a set of previously materialized views over the database, rather than accessing the database relations. The problem has received significant attention because of its relevance to a wide variety of data management problems, such as data integration, query optimization, and the maintenance of physical data independence. To date, the performance of proposed algorithms has received very little attention, and in particular, their scale up in the presence of a large number of views is unknown. We first analyze two previous algorithms, the bucket algorithm and the inverse-rules, and show their deficiencies. We then describe the MiniCon, a novel algorithm for finding the maximally-contained rewriting of a conjunctive query using a set of conjunctive views. We present the first experimental study of algorithms for answering queries using views. The study shows that the MiniCon scales up well and significantly outperforms the previous algorithms. We describe an extension of the MiniCon to handle comparison predicates, and show its performance experimentally. Finally, we describe how the MiniCon can be extended to the context of query optimization. Received: 15 October 2000 / Accepted: 15 April 2001 Published online: 28 June 2001     

The Work-Family Interface and Burnout.

This study examined fluctuations in the experience of conflict between work and family and burnout in different phases of business travel as well as the relationship between work-family conflict (WFC) and burnout among 58 business travelers. Travelers completed questionnaires at 3 points in time: prior to going abroad, during the stay abroad, and after their return. An analysis of variance detected a different pattern of fluctuations in the levels of both WFC and burnout according to gender. Furthermore, while WFC at the pretrip and midtrip periods did not predict burnout in subsequent measurements, pretrip burnout did predict WFC during the trip and after the trip (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Different orientations of males and females in computer-mediated negotiations

This paper examines the existence of gender differences in computer mediated (CM) negotiations where “gender differences” refers to the differential patterns of behavior of males and females proposed by Rubin and Brown (Rubin, J. Z., & Brown, B. R. (1975). Bargainers as individuals. In The social psychology of bargaining and negotiation (pp. 157–196). New York: Academic Press). Namely, males are more profit oriented and females are more relationship oriented. External manipulations encouraging cooperativeness with other negotiators either by profitable or social incentives were inserted in the negotiations performed within the Colored Trails (CT) game framework. The negotiators included 27 females and 33 males who negotiated in foursomes via computers. In the first study we focused on independent negotiators whose success was not crucially dependent on the other party. In the second study negotiators were dependent upon one another, encouraging integrative solutions. The findings reveal that the social incentive (team factor) positively affected the females’ cooperativeness in contrast to males who were slightly less cooperative. On the other hand, profitable incentive influenced the males’ cooperativeness level, while no change was shown by females, which is consistent with Rubin and Brown’s distinction. These tendencies were reduced when playing with a non-reciprocal simulated agent. The causes for gender differences in CM as well as in face-to-face (FTF) negotiations are discussed.