A time sequence is a discrete sequence of vahtes, e.g.temperature measurements, varying over time.Conventional indexes for time sequences are built on the time domain and cannot derd with inverse queries on a time sequence (i.e.computing the times when the values satis~some conditions).To process an inverse query the entire time sequence has to be scanned.This paper presents a dynamic indexing technique on the vahte domain for large time sequences which can be implemented using regular ordered indexing techniques (e.g.B-trees).Our index (termed ZP-irtdex) dramatically improves the query processing time of inverse queries compared to linear scanning.For periodic time sequences that have a limited range and precision on their value domain (most time sequences have this property), the W-index has an upper bound for insertion time and search time.

We propose a distributed deadlock detection algorithm for distributed computer systems. We consider two types of resources, depending on whether the remote resource lock granularity and mode can or cannot be determined without access to the remote resource site. We present the algorithm, its performance analysis, and an informal argument about its correctness. The proposed algorithm has a hierarchical design intended to detect the most frequent deadlocks with maximum efficiency.

In this paper we report our preliminary re sults in the correctness of concurrency control and we outline a new approach to concurrency control. First, we derive necessary and sufficient condition for the serializability of concurrent execution of transactions, regardless of the underlying mech anism (i. e. locking or time stamps) controlling such execution. We then outline a proposal for a new approach to concurrency control which is motivated by the results presented in the first part of the paper. The approach is based on detection of nonserializable actions and subsequent recovery rather than the prevention or avoidance methods which are used by existing concurrency control mechanisms.

A principal problem with dynamic validation of transactions with respect to a set of integrity assertions is the cost associated with the evaluation of such assertions. Although several methods of dynamic validation of transactions have been proposed there has been little attempt to analyze and to compare the performance of different validation methods. In this paper we evaluate compile time, run time, postexecution time, and mixed (run time --- postexecution time) validation methods for two semantic integrity subsystem designs. In one case we assume that the arguments of all integrity assertions are stored in secondary slow access memory and in the second we assume that the database is partitioned so that some data used for transaction validation are stored in fast access form.