ACM Transactions on Database Systems
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Preference formulas in relational queries
The handling of user preferences is becoming an increasingly important issue in present-day information systems. Among others, preferences are used for
information filtering and extraction
to reduce the volume of data presented to the user. They are also used to keep track of
user profiles
and formulate
policies
to improve and automate decision making.We propose here a simple, logical framework for formulating preferences as
preference formulas
. The framework does not impose any restrictions on the preference relations, and allows arbitrary operation and predicate signatures in preference formulas. It also makes the composition of preference relations straightforward. We propose a simple, natural embedding of preference formulas into relational algebra (and SQL) through a single
winnow
operator parameterized by a preference formula. The embedding makes possible the formulation of complex preference queries, for example, involving aggregation, by piggybacking on existing SQL constructs. It also leads in a natural way to the definition of further, preference-related concepts like ranking. Finally, we present general algebraic laws governing the winnow operator and its interactions with other relational algebra operators. The preconditions on the applicability of the laws are captured by logical formulas. The laws provide a formal foundation for the algebraic optimization of preference queries. We demonstrate the usefulness of our approach through numerous examples.
ACM Transactions on Database Systems - Tập 28 Số 4 - Trang 427-466 - 2003
ChronicleDB Reactive security monitoring, self-driving cars, the Internet of Things (IoT), and many other novel applications require systems for both writing events arriving at very high and fluctuating rates to persistent storage as well as supporting analytical ad hoc queries. As standard database systems are not capable of delivering the required write performance, log-based systems, key-value stores, and other write-optimized data stores have emerged recently. However, the drawbacks of these systems are a fair query performance and the lack of suitable instant recovery mechanisms in case of system failures.
In this article, we present ChronicleDB, a novel database system with a storage layout tailored for high write performance under fluctuating data rates and powerful indexing capabilities to support a variety of queries. In addition, ChronicleDB offers low-cost fault tolerance and instant recovery within milliseconds. Unlike previous work, ChronicleDB is designed either as a serverless library to be tightly integrated in an application or as a standalone database server. Our results of an experimental evaluation with real and synthetic data reveal that ChronicleDB clearly outperforms competing systems with respect to both write and query performance.
ACM Transactions on Database Systems - Tập 44 Số 4 - Trang 1-45 - 2019
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