Enforcing local consistency is a well-known technique to simplify the evaluation of conjunctive queries. It consists of repeatedly taking the semijion between every pair of (relations associated with) query atoms, until the procedure stabilizes. If some ...

We study functional and multivalued dependencies over SQL tables with NOT NULL constraints. Under a no-information interpretation of null values we develop tools for reasoning. We further show that in the absence of NOT NULL constraints the associated ...

Most B-tree papers assume that all N keys have the same size K, that F = B/K keys fit in a disk block, and therefore that the search cost is O(log_f+1 N) block transfers. When keys have variable size, however, B-tree operations have no nontrivial ...

The hash table, especially its external memory version, is one of the most important index structures in large databases. Assuming a truly random hash function, it is known that in a standard external hash table with block size b, searching for a ...

It is well known that a search engine can significantly benefit from an auxiliary database, which can suggest interpretations of the search query by means of the involved concepts and their interrelationship. The difficulty is to translate abstract ...

Schema mappings are high-level specifications that describe the relationship between two database schemas; they are considered to be the essential building blocks in data exchange and data integration, and have been the object of extensive research ...

XML Schema Definitions (XSDs) can be adequately abstracted by the single-type regular tree languages. It is well-known, that these form a strict subclass of the robust class of regular unranked tree languages. Sadly, in this respect, XSDs are not closed ...

Abiteboul et al. initiated the systematic study of distributed XML documents consisting of several logical parts, possibly located on different machines. The physical distribution of such documents immediately raises the following question: how can a ...

In the last few years, a lot of attention has been paid to the specification and subsequent manipulation of schema mappings, a problem which is of fundamental importance in metadata management. There have been many achievements in this area, and ...

We study highly expressive query languages such as datalog, fixpoint, and while-languages on probabilistic databases. We generalize these languages such that computation steps (e.g. datalog rules) can fire probabilistically. We define two possible ...

We describe an algorithm that evaluates queries over probabilistic databases using Mobius' inversion formula in incidence algebras. The queries we consider are unions of conjunctive queries (equivalently: existential, positive First Order sentences), ...

The notion of certain answers arises when one queries incompletely specified databases, e.g., in data integration and exchange scenarios, or databases with missing information. While in the relational case this notion is well understood, there is no ...

A natural way for capturing uncertainty in the relational data model is by having relations that violate their primary key constraint, that is, relations in which distinct tuples agree on the primary key. A repair (or possible world) of a database is ...

Databases in real life are often neither entirely closed-world nor entirely open-world. Indeed, databases in an enterprise are typically partially closed, in which a part of the data is constrained by master data that contains complete information about ...

"Privacy" and "utility" are words that frequently appear in the literature on statistical privacy. But what do these words really mean? In recent years, many problems with intuitive notions of privacy and utility have been uncovered. Thus more formal ...

Differential privacy is a robust privacy standard that has been successfully applied to a range of data analysis tasks. But despite much recent work, optimal strategies for answering a collection of related queries are not known.

We propose the matrix ...

Both semantic and type-based query optimization rely on the idea that queries often exhibit non-trivial rewritings if the state space of the database is restricted. Despite their close connection, these two problems to date have always been studied ...

This paper approaches the incremental view maintenance problem from an algebraic perspective. We construct the algebraic structure of a ring of databases and use it as the foundation of the design of a query calculus that allows to express powerful ...

Cardinality estimation is the problem of estimating the number of tuples returned by a query; it is a fundamentally important task in data management, used in query optimization, progress estimation, and resource provisioning. We study cardinality ...

We give the first optimal algorithm for estimating the number of distinct elements in a data stream, closing a long line of theoretical research on this problem begun by Flajolet and Martin in their seminal paper in FOCS 1983. This problem has ...