Zvi M. Kedem

Pincer Search: A New Algorithm for Discovering the Maximum Frequent Set

Discovering frequent itemsets is a key problem in important data mining applications, such as the discovery of association rules, strong rules, episodes, and minimal keys. Typical algorithms for solving this problem operate in a bottom-up breadth-first search direction. The computation starts from frequent 1-itemsets (minimal length frequent itemsets) and continues until all maximal (length) frequent itemsets are found. During the execution, every frequent itemset is explicitly considered. Such algorithms perform reasonably well when all maximal frequent itemsets are short. However, performance drastically decreases when some of the maximal frequent itemsets are relatively long. We present a new algorithm which combines both the bottom-up and top-down searches. The primary search direction is still bottom-up, but a restricted search is also conducted in the top-down direction. This search is used only for maintaining and updating a new data structure we designed, the maximum frequent candidate set. It is used to prune candidates in the bottom-up search. A very important characteristic of the algorithm is that it does not require explicite examination of every frequent itemset. Therefore the algorithm performs well even when some maximal frequent itemsets are long. As its output, the algorithm produces the maximum frequent set, i.e., the set containing all maximal frequent itemsets, which therefore specifies immediately all frequent itemsets. We evaluate the performance of the algorithm using a well-known benchmark database. The improvements can be up to several orders of magnitude, compared to the best current algorithms.

Consistency in Hierarchical Database Systems

The problems of locking and consistency m database systems are examined It is assumed that each transacuon, when executed alone, transforms a consistent state into a consistent state A set of conditions is derived to guarantee that when transactions are processed concurrently, the results are the same as would be obtained by processing the transactmns serially These conditions are used to estabhsh a locking protocol in Merarchmal database systems The locking protocol allows transaeuons to request new locks after releasing a lock. However, a data item may be locked at most once as a result of each transacUon It ~s shown that the protocol ensures consistency and that tt ts deadlock free.

Synthesizing linear array algorithms from nested FOR loop algorithms

The mapping of algorithms structured as depth-p nested FOR loops into special-purpose systolic VLSI linear arrays is addressed. The mappings are done by using linear functions to transform the original sequential algorithms into a form suitable for parallel execution on linear arrays. A feasible mapping is derived by identifying formal criteria to be satisfied by both the original sequential algorithm and the proposed transformation function. The methodology is illustrated by synthesizing algorithms for matrix multiplication and a version of the Warshall-Floyd transitive closure algorithm. >

Pincer-search: an efficient algorithm for discovering the maximum frequent set

Discovering frequent itemsets is a key problem in important data mining applications, such as the discovery of association rules, strong rules, episodes, and minimal keys. Typical algorithms for solving this problem operate in a bottom-up, breadth-first search direction. The computation starts from frequent 1-itemsets (the minimum length frequent itemsets) and continues until all maximal (length) frequent itemsets are found. During the execution, every frequent itemset is explicitly considered. Such algorithms perform well when all maximal frequent itemsets are short. However, performance drastically deteriorates when some of the maximal frequent itemsets are long. We present a new algorithm which combines both the bottom-up and the top-down searches. The primary search direction is still bottom-up, but a restricted search is also conducted in the top-down direction. This search is used only for maintaining and updating a new data structure, the maximum frequent candidate set. It is used to prune early candidates that would be normally encountered in the bottom-up search. A very important characteristic of the algorithm is that it does not require explicit examination of every frequent itemset. We evaluate the performance of the algorithm using well-known synthetic benchmark databases, real-life census, and stock market databases.

Charlotte: metacomputing on the Web

Abstract Parallel computing on local area networks is generally based on mechanisms that specifically target the properties of the local area network environment. However, these mechanisms do not effectively extend to wide area networks due to issues such as heterogeneity, security, and administrative boundaries. We present a system which enables application programmers to write parallel programs in Java and allows Java-capable browsers to execute parallel tasks. It comprises a virtual machine model which isolates the program from the execution environment, and a runtime system realizing this virtual machine on the Web. Load balancing and fault masking are transparently provided by the runtime system.

Mapping nested loop algorithms into multidimensional systolic arrays

Consideration is given to transforming depth p-nested for loop algorithms into q-dimensional systolic VLSI arrays where 1 >

Combining tentative and definite executions for very fast dependable parallel computing

We present a general and efficient strategy for computing mtustly on unreliable parallel machines. The model of a parallel machine that we use is a CRCW PRAM with dynamic resource fluctuations: processors can fail during the computation, and may possibly bc restored later. We first introduce the notions of dejinite and tentatitie algorithms for executing a single parallel step of an ideal parallel machine on the unreliable machine. A definite algorithm is one that guarantees a correct “This research was partially supported by the National Science Foundation under grant number CCR88-6949 and by the EEC ESPRIT Basic Research Actions Project ALCOM (No 3075). t Cwent ~dress: Ecole des Hautes Etudes en Informatique, Univemit4 Fterk Descartes, 45, rue des Saints-P&res, 76006 Paris, i?kIce. Permanent address: Department of Computer Science, New York University, 251 Mercer St., New York, NY 10012-1185, USA; +1 (212) 998-3101; kedem@nyu.edu. This .suthor’s research was conducted while he was visiting the IBM Research Division at the T. J. Watson Research Center and the Institute for Advanced Computer Studies at the University of Maryland.

Parallel processing on networks of workstations: a fault-tolerant, high performance approach

~M ~~~ Divigion, T. J. Watson fi~ew~ Centw, p, 0. Box 704, Yorktown Heights, NY 10598, USA; +1 (914] 784-7846; kpalam~ibrn.corn. i Computff S&we Division, University of Csdifonnia, Davis, CA 95616, USA; +1 (916) 752-1287; raghunatWris.ucdavis.edu. Part of this author’s research was conducted while he was visiting New York Univemity. ?Computm TeclMology Institute, Patras University, P. O. Box 1122, 26110 Patras, Greece; +30 (61) 225-073; spirakis~ grpatvxl.bitnet. Tbis author’s research was conducted while he was visiting New York University. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commemal advantage, the ACM copyright notice and the title of the pubhcation and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. @ 1991 ACM 089791-397-3/91/0004/038 1

A distributed adaptive cache update algorithm for the dynamic source routing protocol

1.50 Raghunathan

Locking Protocols: From Exclusive to Shared Locks

P. G. Spirakis~ execution of a step, while a tentative algorithm is one that is “highly likely” to produce a correct execution of a step on the unreliable machine. We show that any definite execution of one step requires Cl(log n) time on an *processor unreliable machine, even if all the processors functioned perfectly, This implies an