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12
Query evaluation techniques for large databases
 ACM COMPUTING SURVEYS
, 1993
"... Database management systems will continue to manage large data volumes. Thus, efficient algorithms for accessing and manipulating large sets and sequences will be required to provide acceptable performance. The advent of objectoriented and extensible database systems will not solve this problem. On ..."
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Cited by 644 (9 self)
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Database management systems will continue to manage large data volumes. Thus, efficient algorithms for accessing and manipulating large sets and sequences will be required to provide acceptable performance. The advent of objectoriented and extensible database systems will not solve this problem. On the contrary, modern data models exacerbate it: In order to manipulate large sets of complex objects as efficiently as today’s database systems manipulate simple records, query processing algorithms and software will become more complex, and a solid understanding of algorithm and architectural issues is essential for the designer of database management software. This survey provides a foundation for the design and implementation of query execution facilities in new database management systems. It describes a wide array of practical query evaluation techniques for both relational and postrelational database systems, including iterative execution of complex query evaluation plans, the duality of sort and hashbased set matching algorithms, types of parallel query execution and their implementation, and special operators for emerging database application domains.
RainForest  a Framework for Fast Decision Tree Construction of Large Datasets
 In VLDB
, 1998
"... Classification of large datasets is an important data mining problem. Many classification algorithms have been proposed in the literature, but studies have shown that so far no algorithm uniformly outperforms all other algorithms in terms of quality. In this paper, we present a unifying framework fo ..."
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Cited by 95 (9 self)
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Classification of large datasets is an important data mining problem. Many classification algorithms have been proposed in the literature, but studies have shown that so far no algorithm uniformly outperforms all other algorithms in terms of quality. In this paper, we present a unifying framework for decision tree classifiers that separates the scalability aspects of algorithms for constructing a decision tree from the central features that determine the quality of the tree. This generic algorithm is easy to instantiate with specific algorithms from the literature (including C4.5, CART,
A lineartime probabilistic counting algorithm for database applications
 ACM Transactions on Database Systems
, 1990
"... We present a probabilistic algorithm for counting the number of unique values in the presence of duplicates. This algorithm has O(q) time complexity, where q is the number of values including duplicates, and produces an estimation with an arbitrary accuracy prespecified by the user using only a smal ..."
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Cited by 92 (5 self)
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We present a probabilistic algorithm for counting the number of unique values in the presence of duplicates. This algorithm has O(q) time complexity, where q is the number of values including duplicates, and produces an estimation with an arbitrary accuracy prespecified by the user using only a small amount of space. Traditionally, accurate counts of unique values were obtained by sorting, which has O(q log q) time complexity. Our technique, called linear counting, is based on hashing. We present a comprehensive theoretical and experimental analysis of linear counting. The analysis reveals an interesting result: A load factor (number of unique values/hash table size) much larger than 1.0 (e.g., 12) can be used for accurate estimation (e.g., 1 % of error). We present this technique with two important applications to database problems: namely, (1) obtaining the column cardinality (the number of unique values in a column of a relation) and (2) obtaining the join selectivity (the number of unique values in the join column resulting from an unconditional join divided by the number of unique join column values in the relation to he joined). These two parameters are important statistics that are used in relational query optimization and physical database design.
On synopses for distinctvalue estimation under multiset operations
 IN SIGMOD
, 2007
"... The task of estimating the number of distinct values (DVs) in a large dataset arises in a wide variety of settings in computer science and elsewhere. We provide DV estimation techniques that are designed for use within a flexible and scalable “synopsis warehouse” architecture. In this setting, incom ..."
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Cited by 37 (7 self)
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The task of estimating the number of distinct values (DVs) in a large dataset arises in a wide variety of settings in computer science and elsewhere. We provide DV estimation techniques that are designed for use within a flexible and scalable “synopsis warehouse” architecture. In this setting, incoming data is split into partitions and a synopsis is created for each partition; each synopsis can then be used to quickly estimate the number of DVs in its corresponding partition. By combining and extending a number of results in the literature, we obtain both appropriate synopses and novel DV estimators to use in conjunction with these synopses. Our synopses can be created in parallel, and can then be easily combined to yield synopses and DV estimates for arbitrary unions, intersections or differences of partitions. Our synopses can also handle deletions of individual partition elements. We use the theory of order statistics to show that our DV estimators are unbiased, and to establish moment formulas and sharp error bounds. Based on a novel limit theorem, we can exploit results due to Cohen in order to select synopsis sizes when initially designing the warehouse. Experiments and theory indicate that our synopses and estimators lead to lower computational costs and more accurate DV estimates than previous approaches.
Estimating Alphanumeric Selectivity in the Presence of Wildcards
 In SIGMOD
, 1996
"... Success of commercial query optimizers and database management systems (objectoriented or relational) depend on accurate cost estimation of various query reorderings [BGI]. Estimating predicate selectivity, or the fraction of rows in a database that satisfy a selection predicate, is key to determin ..."
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Cited by 33 (2 self)
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Success of commercial query optimizers and database management systems (objectoriented or relational) depend on accurate cost estimation of various query reorderings [BGI]. Estimating predicate selectivity, or the fraction of rows in a database that satisfy a selection predicate, is key to determining the optimal join order. Previous work has concentrated on estimating selectivity for numeric fields [ASW, HaSa, IoP, LNS, SAC, WVT]. With the popularity of textual data being stored in databases, it has become important to estimate selectivity accurately for alphanumeric fields. A particularly problematic predicate used against alphanumeric fields is the SQL like predicate [Dat]. Techniques used for estimating numeric selectivity are not suited for estimating In this paper, we study for the first time the problem of estimating alphanumeric selectivity in the presence of wildcards. Based on the intuition that the model built by a data compressor on an input text encapsulates information about common substrings in the text, we develop a technique based on the suffix tree data structure to estimate alphanumeric selectivity. In a statistics generation pass over the database, we construct a compact suffix treebased structure from the columns of the database. We then look at three families of methods that utilize this structure to estimate selectivity during query plan costing, when a query with predicates on alphanumeric attributes contains wildcards in the predicate. We evaluate our methods empirically in the context of the TPCD benchmark. We study our methods experimentally against a variety of query patterns and identify five techniques that hold promise.
Random Sampling from Databases  A Survey
 Statistics and Computing
, 1994
"... This paper reviews recent literature on techniques for obtaining random samples from databases. We begin with a discussion of why one would want to include sampling facilities in database management systems. We then review basic sampling techniques used in constructing DBMS sampling algorithms, e.g. ..."
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Cited by 22 (0 self)
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This paper reviews recent literature on techniques for obtaining random samples from databases. We begin with a discussion of why one would want to include sampling facilities in database management systems. We then review basic sampling techniques used in constructing DBMS sampling algorithms, e.g., acceptance/rejection and reservoir sampling. A discussion of sampling from various data structures follows: B + trees, hash files, spatial data structures (including Rtrees and quadtrees)). Algorithms for sampling from simple relational queries, e.g., single relational operators such as selection, intersection, union, set difference, projection, and join are then described. We then describe sampling for estimation of aggregates (e.g., the size of query results). Here we discuss both clustered sampling, and sequential sampling approaches. Decision theoretic approaches to sampling for query optimization are reviewed. DRAFT of March 22, 1994. 1 Introduction In this paper we sur...
Online Prediction Algorithms for Databases and Operating Systems
, 1995
"... In making online decisions, computer systems are inherently trying to predict future events. Typical decision problems in computer systems translate to three prediction scenarios: predicting what event is going to happen in the future, when a specific event will take place, or how much of something ..."
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Cited by 16 (1 self)
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In making online decisions, computer systems are inherently trying to predict future events. Typical decision problems in computer systems translate to three prediction scenarios: predicting what event is going to happen in the future, when a specific event will take place, or how much of something is going to happen. In this thesis, we develop practical algorithms for specific instances of these three prediction scenarios, and prove the goodness of our algorithms via analytical and experimental methods. We study each of the three prediction scenarios via motivating systems problems. The problem of prefetching requires a prediction of which page is going to be next requested by a user. The problem of disk spindown in mobile machines, modeled by the renttobuy framework, requires an estimate of when the next disk access is going to happen. Query optimizers choose a database access strategy by predicting or estimating selectivity, i.e., by estimating the size of a query result. We an...
On Adaptive Sampling
, 1990
"... . We analyze the storage/accuracy tradeoff of an adaptive sampling algorithm due to Wegman that makes it possible to evaluate probabilistically the number of distinct elements in a large file stored on disk. 1 Introduction A problem that naturally arises in query optimization of data base systems ..."
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Cited by 13 (2 self)
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. We analyze the storage/accuracy tradeoff of an adaptive sampling algorithm due to Wegman that makes it possible to evaluate probabilistically the number of distinct elements in a large file stored on disk. 1 Introduction A problem that naturally arises in query optimization of data base systems [1] is to estimate the number of distinct elements (also called cardinality) of a large collection of data with unpredictable replications. The trivial solution that consists in building a list of distinct elements is usually too much resource consuming both in terms of storage and processing time requirements. In [4] the authors have presented a solution called Probabilistic Counting that estimates the cardinality of a large file typically stored on disk; when using m words of incore memory the algorithm presents an expected relative accuracy close to 0:78 p m; and it performs only a constant number of operations per element of the file. Wegman [11] has proposed an interesting alter...
Toward automated largescale information integration and discovery
 In Data Management in a Connected World
, 2005
"... Abstract. The high cost of data consolidation is the key market inhibitor to the adoption of traditional information integration and data warehousing solutions. In this paper, we outline a nextgeneration integrated database management system that takes traditional information integration, content m ..."
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Cited by 9 (4 self)
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Abstract. The high cost of data consolidation is the key market inhibitor to the adoption of traditional information integration and data warehousing solutions. In this paper, we outline a nextgeneration integrated database management system that takes traditional information integration, content management, and data warehouse techniques to the next level: the system will be able to integrate a very large number of information sources and automatically construct a global business view in terms of “Universal Business Objects”. We describe techniques for discovering, unifying, and aggregating data from a large number of disparate data sources. Enabling technologies for our solution are XML, web services, caching, messaging, and portals for realtime dashboarding and reporting. 1