6654135
Finding interesting associations without support pruning
Association rule mining has heretofore relied on the condition of high support to do its work efficiently. In particular, the well-known a-priori algorithm is only effective when the only rules of interest are relationships that occur very frequently. However, there are a number of applications, such as data mining, identification of similar Web documents, clustering and collaborative filtering, where the rules of interest have comparatively few instances in the data. In these cases, we must look for highly correlated items, or possibly even causal relationships between infrequent items. We develop a family of algorithms for solving this problem, employing a combination of random sampling and hashing techniques. We provide an analysis of the algorithms developed and conduct experiments on real and synthetic data to obtain a comparative performance analysis.
291860
The TSIMMIS Approach to Mediation: Data Models and Languages
TSIMMIS—The Stanford-IBM Manager of Multiple InformationSources—is a system for integrating information. It offers a datamodel and a common query language that are designed to support thecombining of information from many different sources. It also offerstools for generating automatically the components that are needed tobuild systems for integrating information. In this paper we shalldiscuss the principal architectural features and their rationale.
6212306
Constraint checking with partial information
Constraints are a valuable tool for managing information across multiple databases, as well as for general purposes of assuring data integrity. However, efficient implementation of constraint checking is difficult. In this paper we explore techniques for assuring constraint satisfaction without performing a complete evaluation of the constraints. We consider methods that use only constraint definitions, methods that use constraints and updates, and methods that use constraints, updates, and “local” data.
208920048
Integrating Information by Outerjoins and Full Disjunctions.
Our motivation is the piecing together of tidbits of information found on the "web" into a usable information structure. The problem is related to that of computing the natural outerjoin of many relations in a way that preserves all possible connections among facts. Such a computation has been termed a "full disjunction" by Galindo-Legaria. We are thus led to ask the question of when a full disjunction can be computed by some sequence of natural outerjoins. The answer involves a concept of from Fagin [1983] called fl-acyclic hypergraphs." We prove that there is a natural outerjoin sequence producing the full disjunction if and only if the set of relation schemes forms a connected, fl-acyclic hypergraph.
9277235
Index selection for OLAP
On-line analytical processing (OLAP) is a recent and important application of database systems. Typically, OLAP data is presented as a multidimensional "data cube." OLAP queries are complex and can take many hours or even days to run, if executed directly on the raw data. The most common method of reducing execution time is to precompute some of the queries into summary tables (subcubes of the data cube) and then to build indexes on these summary tables. In most commercial OLAP systems today, the summary tables that are to be precomputed are picked first, followed by the selection of the appropriate indexes on them. A trial-and-error approach is used to divide the space available between the summary tables and the indexes. This two-step process can perform very poorly. Since both summary tables and indexes consume the same resource-space-their selection should be done together for the most efficient use of space. The authors give algorithms that automate the selection of summary tables and indexes. In particular, they present a family of algorithms of increasing time complexities, and prove strong performance bounds for them. The algorithms with higher complexities have better performance bounds. However, the increase in the performance bound is diminishing, and they show that an algorithm of moderate complexity can perform fairly close to the optimal.
5323612
A Query Translation Scheme for Rapid Implementation of Wrappers
Wrappers provide access to heterogeneous information sources by converting application queries into source specific queries or commands. In this paper we present a wrapper implementation toolkit that facilitates rapid development of wrappers. We focus on the query translation component of the toolkit, called the converter. The converter takes as input a Query Description and Translation Language (QDTL) description of the queries that can be processed by the underlying source. Based on this the converter decides if an application query is (a) directly supported, i.e., it can be translated to a query of the underlying system following instructions in the QDTL description; (b) logically supported, i.e., logically equivalent to a directly supported query; (c) indirectly supported, i.e., it can be computed by applying a filter, automatically generated by the converter, to the result of a directly supported query.
17355782
On complementary and independent mappings on databases
We define the notion of independent views to indicate whether the range values of the two views may be achieved independently The concept of complementary views indicates when the domain element can be uniquely determined by the range values of the two complementary views We consider the relationship between independent and complementary views In unrestricted domains, a view (but not the identity or empty view) can have more than one complementary, independent view Databases, however, are more restricted domains They are finite power sets A view is monotonic if it preserves inclusion However, in finite power sets when all views are monotonic, if a given view has another view which is independent and complementary, then this view is unique.
22691930
Time and Tape Complexity of Pushdown Automaton Languages
An algorithm is presented which will determine whether any string w in Σ*, of length n, is contained in a language L ⊆ Σ* defined by a two-way nondeterministic pushdown automation. This algorithm requires time n3 when implemented on a random access computer. It requires n4 time and n2 tape when implemented on a multitape Turing machine. If the pushdown automaton is deterministic, the algorithm requires n2 time on a random access computer and n2 log n time on a multitape Turing machine.
209399085
Answering Queries Using Limited External Processors.