Showing papers by "Phokion G. Kolaitis published in 2005"

Schema mappings, data exchange, and metadata management

Abstract: Schema mappings are high-level specifications that describe the relationship between database schemas. Schema mappings are prominent in several different areas of database management, including database design, information integration, data exchange, metadata management, and peer-to-peer data management systems. Our main aim in this paper is to present an overview of recent advances in data exchange and metadata management, where the schema mappings are between relational schemas. In addition, we highlight some research issues and directions for future work.

Peer data exchange

Abstract: In this article, we introduce and study a framework, called peer data exchange, for sharing and exchanging data between peers. This framework is a special case of a full-fledged peer data management system and a generalization of data exchange between a source schema and a target schema. The motivation behind peer data exchange is to model authority relationships between peers, where a source peer may contribute data to a target peer, specified using source-to-target constraints, and a target peer may use target-to-source constraints to restrict the data it is willing to receive, but cannot modify the data of the source peer.A fundamental algorithmic problem in this framework is that of deciding the existence of a solution: given a source instance and a target instance for a fixed peer data exchange setting, can the target instance be augmented in such a way that the source instance and the augmented target instance satisfy all constraints of the settingq We investigate the computational complexity of the problem for peer data exchange settings in which the constraints are given by tuple generating dependencies. We show that this problem is always in NP, and that it can be NP-complete even for “acyclic” peer data exchange settings. We also show that the data complexity of the certain answers of target conjunctive queries is in coNP, and that it can be coNP-complete even for “acyclic” peer data exchange settings.After this, we explore the boundary between tractability and intractability for deciding the existence of a solution and for computing the certain answers of target conjunctive queries. To this effect, we identify broad syntactic conditions on the constraints between the peers under which the existence-of-solutions problem is solvable in polynomial time. We also identify syntactic conditions between peer data exchange settings and target conjunctive queries that yield polynomial-time algorithms for computing the certain answers. For both problems, these syntactic conditions turn out to be tight, in the sense that minimal relaxations of them lead to intractability. Finally, we introduce the concept of a universal basis of solutions in peer data exchange and explore its properties.

System and method for performing a high-level multi-dimensional query on a multi-structural database

Abstract: A multi-structural query system performs a high-level multi-dimensional query on a multi-structural database. The query system enables a user to navigate a search by adding restrictions incrementally. The query system uses a schema to discover structure in a multi-structural database. The query system leaves a choice of nodes to return in response to a query as a constrained set of choices available to the algorithm. The query system further casts the selection of a set of nodes as an optimization. The query system uses pairwise-disjoint collections to capture a concise set of highlights of a data set within the allowed schema. The query system further comprises efficient algorithms that yield approximately optimal solutions for several classes of objective functions.

Preferred representations of Boolean relations

Abstract: We introduce the notion of a plain basis for a co-clone in Post’s lattice. Such a basis is a set of relations B such that every constraint C over a relation in the co-clone is logically equivalent to a conjunction of equalities and constraints over B and the same variables as C; this diers from the usual notion of a basis in that existential quantication of auxiliary variables is not allowed. We give such a basis for every co-clone and in particular for those in the innite part of the lattice; it turns out that most of these bases correspond to sets of propositional clauses, thus providing a strong link between classes of formulas dened for CSP and CNF representations. We then show that a so-called preferred representation of a relation over one of its bases can be computed ecien tly, as well as the minimal co-clone including a given relation, which solves some open structure identication problem as well as the open expressibility problem from database theory.

Exchange, integration, and consistency of data: report on the ARISE/NISR workshop

Abstract: The "ARISE/NISR Workshop on Exchange and Integration of Data" was held at the IBM Center for Advanced Studies, Toronto Lab., between October 7-9, 2004.