Tuple

About: Tuple is a research topic. Over the lifetime, 6513 publications have been published within this topic receiving 146057 citations. The topic is also known as: tuple & ordered tuplet.

Querying Graph Databases

Abstract: Graph data is an emerging model for representing a variety of database contexts ranging from object-oriented databases to hypertext data. Also many of the recursive queries that arise in relational databases are, in practice, graph traversals. In this paper we present a language for searching graph-like databases. The language permits us to express paths in a graph by means of extended regular expressions. The proposed extension is based on the introduction of constructs which permit us i) to define a partial order on the paths used to search the graph and, consequently, on the answers of queries, and ii) to cut off, nondeterministically, tuples with low priority. We present an algebra for partially ordered relations and an algorithm for the computation of path queries. Finally, we present applications to hypertext databases such as the Web.

SaLSa: computing the skyline without scanning the whole sky

Abstract: Skyline queries compute the set of Pareto-optimal tuples in a relation, ie those tuples that are not dominated by any other tuple in the same relation. Although several algorithms have been proposed for efficiently evaluating skyline queries, they either require to extend the relational server with specialized access methods (which is not always feasible) or have to perform the dominance tests on all the tuples in order to determine the result. In this paper we introduce SaLSa (Sort and Limit Skyline algorithm), which exploits the sorting machinery of a relational engine to order tuples so that only a subset of them needs to be examined for computing the skyline result. This makes SaLSa particularly attractive when skyline queries are executed on top of systems that do not understand skyline semantics or when the skyline logic runs on clients with limited power and/or bandwidth.

Skyline with Presorting: Theory and Optimizations

Abstract: There has been interest recently in skyline queries, also called Pareto queries, on relational databases. Relational query languages do not support search for “best” tuples, beyond the order by statement. The proposed skyline operator allows one to query for best tuples with respect to any number of attributes as preferences. In this work, we explore what the skyline means, and why skyline queries are useful, particularly for expressing preference. We describe the theoretical aspects and possible optimizations of an efficiant algorithm for computing skyline queries presented in [6].

Containment of conjunctive queries: beyond relations as sets

Abstract: Conjwzctiue queries are queries over a relational database and are at the core of relational query languages such as SQL. Testing for containment (and equivalence) of such queries arises as part of many advanced features of query optimization, for example, using rnateriahzed views, processing correlated nested queries, semantic query optimization, and global query optimization. Earlier formal work on the topic has examined conjunctive queries over sets of tuples, where each query can be viewed as a function from sets to sets. Containment (and equivalence) of conjunctive queries has been naturally defined based on set mcluslon and has been shown to be an NP-complete problem. Even in SQL, however, queries over multzsets of tuples may be posed. In fact, relations are treated as multisets by default, with duplicates being ehmmated only after explicit requests Thus, in order to reason about containment/equivalence of a large class of SQL queries, it is necessary to consider a generalization of conjunctive queries, in which relations are interpreted as multmets of tuples: The view of a relation as a set of tuples must be generahzed. In this paper we study conjunctive queries over databases in which each tuple has an associated label. This generalized notion of a database allows us to consider relations that are mcsltzsets and relatlons that are fuzzy sets. As a special case, we can also model traditional set-relatlons by making the label associated with a tuple be either “true” (meaning that the tuple is in the relation) or “false” (meaning that the tuple is not in the relation). In order to keep our results general, we consider a variety of label systems, where each label system is essentially a set of conditions on the labels that can be associated with tuples. Once a result is established for a label system, it holds for all mterpretations of relatlons that satisfy these conditions. For example, we present a necessary and sufficient condition for containment of conjunctive queries for label systems of a type that abstracts both the traditional set-relations and fuzzy sets. We also present a different necessary and sufficient condition for containment of a restricted class of conjunctive queries for a label system that abstracts relations as multlsets. Finally, we show that containment of unions of conjunctwe queries is decidable for label systems of the first type and undecidable for label systems of the second type This result underscores the fundamental difference between viewing relations as sets and as multmets, and motivates a closer examination of relatlons as multisets, given them importance in SQL.

Method and apparatus for structuring the querying and interpretation of semistructured information

Abstract: A method is provided for determining how semistructured information is organized in disparate semistructured resources by providing a wrapper to extract information and to provide structured information (e.g., tuples of an SQL database) to a mapper coupled to a standard relational database engine. In a specific embodiment, a querying agent is provided on top of the mapper. Further according to the invention, structured high-level user queries are processed across the disparate semistructured resources using a plurality of wrappers each dedicated to a particular resource.