12892754
Reasoning About Approximate Match Query Results
Join techniques deploying approximate match predicates are fundamental data cleaning operations. A variety of predicates have been utilized to quantify approximate match in such operations and some have been embedded in a declarative data cleaning framework. These techniques return pairs of tuples from both relations, tagged with a score, signifying the degree of similarity between the tuples in the pair according to the specific approximate match predicate. In this paper, we consider the problem of estimating various parameters on the output of declarative approximate join algorithms for planning purposes. Such algorithms are highly time consuming, so precise knowledge of the result size as well as its score distribution is a pressing concern. This knowledge aids decisions as to which operations are more promising for identifying highly similar tuples, which is a key operation for data cleaning. We propose solution strategies that fully comply with a declarative framework and analytically reason about the quality of the estimates we obtain as well as the performance of our strategies. We present the results of a detailed performance evaluation of all strategies proposed. Our experimental results validate our analytical expectations and shed additional light on the quality and performance of our estimation framework. Our study offers a set of simple, fully declarative techniques for this problem, which can be readily deployed in data cleaning systems.
13475547
Towards estimating the number of distinct value combinations for a set of attributes
Accurately and efficiently estimating the number of distinct values for some attribute(s) or sets of attributes in a data set is of critical importance to many database operations, such as query optimization and approximation query answering. Previous work has focused on the estimation of the number of distinct values for a single attribute and most existing work adopts a data sampling approach. This paper addresses the equally important issue of estimating the number of distinct value combinations for multiple attributes which we call COLSCARD (for COLumn Set CARDinality). It also takes a different approach that uses existing statistical information (e.g., histograms) available on the individual attributes to assist estimation. We start with cases where exact frequency information on individual attributes is available, and present a pair of lower and upper bounds on COLSCARD that are consistent with the available information, as well as an estimator of COLSCARD based on probability. We then proceed to study the case where only partial information (in the form of histograms) is available on individual attributes, and show how the proposed estimator can be adapted to this case. We consider two types of widely used histograms and show how they can be constructed in order to obtain optimal approximation. An experimental evaluation of the proposed estimation method on synthetic as well as two real data sets is provided.
7132341
HASE: A Hybrid Approach to Selectivity Estimation for Conjunctive Predicates
Current methods for selectivity estimation fall into two broad categories, synopsis-based and sampling-based. Synopsis-based methods, such as histograms, incur minimal overhead at query optimization time and thus are widely used in commercial database systems. Sampling-based methods are more suited for ad-hoc queries, but often involve high I/O cost because of random access to the underlying data. Though both methods serve the same purpose of selectivity estimation, their interaction in the case of selectivity estimation for conjuncts of predicates on multiple attributes is largely unexplored. Our work aims at taking the best of both worlds, by making consistent use of synopses and sample information when they are both present. To achieve this goal, we propose HASE, a novel estimation scheme based on a powerful mechanism called generalized raking. We formalize selectivity estimation in the presence of single attribute synopses and sample information as a constrained optimization problem. By solving this problem, we obtain a new set of weights associated with the sampled tuples, which has the nice property of reproducing the known selectivities when applied to individual predicates. We discuss different variants of the optimization problem and provide algorithms for solving it. We also provide asymptotic error bounds on the estimate. Extensive experiments are performed on both synthetic and real data, and the results show that HASE significantly outperforms both synopsis-based and sampling-based methods.
1886676
Monitoring k-nearest neighbor queries over moving objects
Many location-based applications require constant monitoring of k-nearest neighbor (k-NN) queries over moving objects within a geographic area. Existing approaches to this problem have focused on predictive queries, and relied on the assumption that the trajectories of the objects are fully predictable at query processing time. We relax this assumption, and propose two efficient and scalable algorithms using grid indices. One is based on indexing objects, and the other on queries. For each approach, a cost model is developed, and a detailed analysis along with the respective applicability is presented. The object-indexing approach is further extended to multi-levels to handle skewed data. We show by experiments that our grid-based algorithms significantly outperform R-tree-based solutions. Extensive experiments are also carried out to study the properties and evaluate the performance of the proposed approaches under a variety of settings.
10594579
Hard Queries can be Addressed with Query Splitting Plus Stepping Stones and Pathways
A key finding of the Reliable Information Access Workshop of 2003 was that in collections like those used for TREC 6-8, there are a number of hard queries for which no current search engine can return a high quality set of results. Our Stepping Stones and Pathways (SSP) approach may yield an effective solution to such hard problems, as well as support exploration of collections of content not well known to a person (with broad interest and/or complex information needs). Our initial and promising testing of SSP had users prepare two separate short queries in order to launch processing. However, since beginning with a single information need is a more typical initial situation, we have extended the SSP research by exploring query splitting, especially as might apply to handling hard queries. This paper summarizes our recent results and identifies some of the future work needed.
28940295
Cyclomatic numbers of connected induced subgraphs
Abstract We give an upper bound for ω( A ), the minimum cyclomatic number of connected induced subgraphs containing a given independent set A of vertices in a given graph G . We also give an upper bound for ω( A ) when G is triangle-free. We show that these two bounds are best possible. Similar results are obtained for A to be a matching of G .
26301648
Data Integrity Framework and Language Support for Active Web Intermediaries
With the maturity of content adaptation technologies (such as I-CAP and OPES) in web intermediaries and of content personalization in the network, data integrity has already become a key concern when such technologies are deployed. To address this issue, we propose a data integrity framework with the following functionalities: (i) a server can specify its authorizations, (ii) active web intermediaries can provide value-added services in accordance with the server’s intentions, and more importantly, (iii) a client is facilitated to verify the received message with the server’s authorizations and intermediaries’ footprints. With the actual implementation of our data integrity framework in web (content and proxy) servers and clients, we show the feasibility and practicability of our proposed design through its low performance overhead and possible data (re)use.
8512382
Five-Connected Toroidal Graphs Are Hamiltonian
We prove that every edge in a 5-connected graph embedded in the torus is contained in a Hamilton cycle. Our proof is constructive and implies a polynomial time algorithm for finding a Hamilton cycle.
11130888
On 3-connected graphs with contractible edge covers of size k
Abstract We consider 3-connected graphs whose contractible edges can be covered by k vertices and show that they can be divided into finitely many infinite classes of graphs.