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1.
The problem of managing and querying inconsistent databases has been deeply investigated in the last few years. As the problem of consistent query answering is hard in the general case, most of the techniques proposed so far have an exponential complexity. Polynomial techniques have been proposed only for restricted forms of constraints (such as functional dependencies) and queries. In this paper, a technique for computing “approximate” consistent answers in polynomial time is proposed, which works in the presence of a wide class of constraints (namely, full constraints) and Datalog queries. The proposed approach is based on a repairing strategy where update operations assigning an undefined truth value to the “reliability” of tuples are allowed, along with updates inserting or deleting tuples. The result of a repair can be viewed as a three-valued database which satisfies the specified constraints. In this regard, a new semantics (namely, partial semantics) is introduced for constraint satisfaction in the context of three-valued databases, which aims at capturing the intuitive meaning of constraints under three-valued logic. It is shown that, in order to compute “approximate” consistent query answers, it suffices to evaluate queries by taking into account a unique repair (called deterministic repair), which in some sense “summarizes” all the possible repairs. The so obtained answers are “approximate” in the sense that are safe (true and false atoms in the answers are, respectively, true and false under the classical two-valued semantics), but not complete.  相似文献   

2.
The video databases have become popular in various areas due to the recent advances in technology. Video archive systems need user-friendly interfaces to retrieve video frames. In this paper, a user interface based on natural language processing (NLP) to a video database system is described. The video database is based on a content-based spatio-temporal video data model. The data model is focused on the semantic content which includes objects, activities, and spatial properties of objects. Spatio-temporal relationships between video objects and also trajectories of moving objects can be queried with this data model. In this video database system, a natural language interface enables flexible querying. The queries, which are given as English sentences, are parsed using link parser. The semantic representations of the queries are extracted from their syntactic structures using information extraction techniques. The extracted semantic representations are used to call the related parts of the underlying video database system to return the results of the queries. Not only exact matches but similar objects and activities are also returned from the database with the help of the conceptual ontology module. This module is implemented using a distance-based method of semantic similarity search on the semantic domain-independent ontology, WordNet.  相似文献   

3.
A method is presented to prevent anomalies from affecting the design of a relational database. The approach, called the logical design tool (LDT), can also be used as an educational tool for the relational database. It allows certain problems that arise when the data is manipulated to be detected during design. An overview of LDT is followed by a discussion of its functions and its application  相似文献   

4.
We consider the problem of retrieving consistent answers over databases that might be inconsistent with respect to a set of integrity constraints. In particular, we concentrate on sets of constraints that consist of key dependencies, and we give an algorithm that computes the consistent answers for a large and practical class of conjunctive queries. Given a query q, the algorithm returns a first-order query Q (called a query rewriting) such that for every (potentially inconsistent) database I, the consistent answers for q can be obtained by evaluating Q directly on I.  相似文献   

5.
In recent years, several attempts have been made to define query languages characterized by both high expressive power and easy query formulation. Several issues concern graphical applications, based on the diagrammatic representation of a semantic model and visual interaction. This paper describes the architecture and the implementation of a graphical query system, based on the diagrammatic representation of entity relationship schemata. The query language underlying the system allows the formulation of recursive queries; moreover, user interaction in both managing diagrams and expressing queries is simplified by the presence of a fully visual environment and a rich set of interaction strategies.  相似文献   

6.
One of the main objectives of third generation databases is to design database management systems which provide users with more and more functionalities. In such a wide context, various proposals have been made in order to introduce some kind of explicit or implicit flexibility into user queries. In this paper, we propose a classification of the various approaches dealing with imprecise queries. Moreover, we show that the approach based on fuzzy sets is powerful enough to answer a wide range of imprecise queries in an appropriate way and to support the expression of the capabilities available in the other classes of solutions. An outline of an SQL-like language allowing for a variety of imprecise queries is also presented.  相似文献   

7.
Modeling and querying fuzzy spatiotemporal databases   总被引:1,自引:0,他引:1  
Modeling spatiotemporal data, in particular fuzzy and complex spatial objects representing geographic entities and relations, is a topic of great importance in geographic information systems, computer vision, environmental data management systems, etc. Because of complex requirements, it is challenging to represent spatiotemporal data and its features in databases and to effectively query them. This article presents a new approach to model and query the spatiotemporal data of fuzzy spatial and complex objects and/or spatial relations. In our case study, we use a meteorological database application in an intelligent database architecture, which combines an object-oriented database with a knowledgebase for modeling and querying spatiotemporal objects.  相似文献   

8.
9.
Trigger querying is the problem of finding, given a system M and an LTL formula φ, the set of scenarios that trigger φ in M; that is, the language L of finite computations of M such that all infinite computations that have a prefix in L continue with a suffix that satisfies φ. Trigger querying significantly extends query checking, which seeks propositional solutions, and is an extremely useful methodology for system exploration and understanding. The weakness of trigger querying lies in the fact that the size of the solution is linear in the size of the system. For trigger querying to become feasible in practice, we must offer solutions to cope with systems of big, and possibly infinite, state spaces. In this paper we describe an abstraction-refinement framework for trigger querying. Instead of reasoning about the system M, we reason about an abstraction of it and return to the user two languages that under- and over-approximate the language L of computations that trigger φ in M. We describe an automata-theoretic approach for refining and reducing the gap between the approximations and show how, unlike classical counterexample-based refinement approaches, here it is possible to symbolically handle batches of counterexamples. We show that our framework is robust and can be applied also for classical query checking as well as variants and extensions of trigger querying.  相似文献   

10.
The widespread use of graph-based models for representing data collections (e.g. object-oriented data, XML data, etc.) has stimulated the database research community to investigate the problem of defining declarative languages for querying graph-like databases. In this paper, a new framework for querying graph-like data based on graph grammars is proposed. The new paradigm allows us to verify structural properties of graphs and to extract sub-graphs. More specifically, a new form of query (namely graph query) is proposed, consisting in a particular graph grammar which defines a class of graphs to be matched on the graph representing the database. Thus, differently from path queries, the answer of a graph query is not just a set of nodes, but a subgraph, extracted from the input graph, which satisfies the structural properties defined by the graph grammar. Expressiveness and complexity of different forms of graph queries are discussed, and some practical applications are shown.  相似文献   

11.
12.
The Web offers a single user interface to data sharing across heterogeneous and autonomous databases, but it was not designed to handle the rigid DBMS protocols and data formats used by relational and object-oriented databases. WebFindIt is an ongoing project to develop the database equivalent of the World Wide Web-namely, a World Wide Database-through a middleware infrastructure for describing, locating, and accessing data from any kind of Web-accessible database. A special-purpose language, Web-Tassili, supports the definition and manipulation of middleware constructs for organizing the information space. An implementation of WebFindIt combines Java, CORBA and database technologies  相似文献   

13.
This paper presents a framework for querying inconsistent databases in the presence of functional dependencies. Most of the works dealing with the problem of extracting reliable information from inconsistent databases are based on the notion of repair, a minimal set of tuple insertions and deletions which leads the database to a consistent state (called repaired database), and the notion of consistent query answer, a query answer that can be obtained from every repaired database. In this work, both the notion of repair and query answer differ from the original ones. In the presence of functional dependencies, tuple deletions are the only operations that are performed in order to restore the consistency of an inconsistent database. However, deleting a tuple to remove an integrity violation potentially eliminates useful information in that tuple. In order to cope with this problem, we adopt a notion of repair, based on tuple updates, which allows us to better preserve information in the source database. A drawback of the notion of consistent query answer is that it does not allow us to discriminate among non-consistent answers, namely answers which can be obtained from a non-empty proper subset of the repaired databases. To obtain more informative query answers, we propose the notion of probabilistic query answer, that is query answers are tuples associated with probabilities. This new semantics of query answering over inconsistent databases allows us to give a measure of uncertainty to query answers. We show that the problem of computing probabilistic query answers is FP #P -complete. We also propose a technique for computing probabilistic answers to arbitrary relational algebra queries.  相似文献   

14.
Although widely advocated as a tool for the conceptual modelling of data, the Entity-Relationship (E-R) model [4] and its extensions are generally lacking in constructs to model the dynamic nature of the real world, making them inadequate for designing temporal databases. This research first extends the E-R model to a Temporal Event-Entity-Relationship Model (TEERM), by introducing events as an additional construct. Second, a method is proposed for mapping this conceptual model into a temporal relational model for the logical design of temporal relational databases with a corresponding set of integrity constraints. The model is illustrated with an example and evaluated using a set of criteria proposed by Batini et al. [2]. The model appears to be expressive, simple and easy to use, and should, therefore, aid the temporal database design process significantly.  相似文献   

15.
As the size and efficiency of computers increases, it is clear that they will be used for extremely large file information storage and retrieval banks, in particular for non-scientific documents and data. Such an information bank might be, for example, the legal code for a large country or even the legal codes of all countries. Another example might be individual medical histories for a large population base, possibly the whole world. Storage and retrieval algorithms for such large files present special problems. It is no longer feasible, for instance, for the computer to consider every item in the memory in order to retrieve a designated subset. The problem, then, is how to classify the information, that is, divide it up into disjoint categories so that retrieval is feasible, efficient, and accurate. The present paper presents a general approach or logical framework for handling such problems. The basic observation is that classification really amounts to introducing an equivalence relation on the universal set of all the items in the file. The problem is how to define these equivalence relations in a natural manner, that is, in a manner which reflects something of the structure of the information and which thus allows us to store and retrieve the information in a structured fashion. This classification procedure is not conceived as being an algorithm but rather a mathematical procedure on which various algorithms can be based. This procedure can be described as follows: First a very broad, initial classification is made. For each such classification, there is a standard or canonical form. The canonical form involves some finite number of parameters. Syntactically these parameters are just terms of various sorts, but our approach is to consider rather the universe of values of each parameter. This is the semantic universe associated with the given parameter. These semantic universes are seen to have a very natural structure when they are considered in a certain way as subcollections of a type-theoretic universe based on some concrete set (such as the set of people, the set of married couples, etc). This structure allows us to define the desired equivalence in a natural way on a given semantic universe. Taking the conjunction of the parameters occurring in a given canonical form we thus get a classification for the sentences having that canonical form. Since this obtains for each canonical form, we thus have a classification for the whole information bank. Concrete examples are given to illustrate the applicability of this approach. The approach is, in fact, a mathematical generalization of a concrete case already treated by this method.  相似文献   

16.
The practical advantage of logical databases is the inferencing capability they provide. An important theoretical effect is the clarification of semantic issues, through logic to model theory.  相似文献   

17.
A framework for knowledge discovery and evolution in databases   总被引:8,自引:0,他引:8  
A concept for knowledge discovery and evolution in databases is described. The key issues include: using a database query to discover new rules; using not only positive examples (answer to a query), but also negative examples to discover new rules; and harmonizing existing rules with the new rules. A tool for characterizing the exceptions in databases and evolving knowledge as a database evolves is developed  相似文献   

18.
Hunter and Konieczny explored the relationships between measures of inconsistency for a belief base and the minimal inconsistent subsets of that belief base in several of their papers. In particular, an inconsistency value termed MIV C , defined from minimal inconsistent subsets, can be considered as a Shapley Inconsistency Value. Moreover, it can be axiomatized completely in terms of five simple axioms. MinInc, one of the five axioms, states that each minimal inconsistent set has the same amount of conflict. However, it conflicts with the intuition illustrated by the lottery paradox, which states that as the size of a minimal inconsistent belief base increases, the degree of inconsistency of that belief base becomes smaller. To address this, we present two kinds of revised inconsistency measures for a belief base from its minimal inconsistent subsets. Each of these measures considers the size of each minimal inconsistent subset as well as the number of minimal inconsistent subsets of a belief base. More specifically, we first present a vectorial measure to capture the inconsistency for a belief base, which is more discriminative than MIV C . Then we present a family of weighted inconsistency measures based on the vectorial inconsistency measure, which allow us to capture the inconsistency for a belief base in terms of a single numerical value as usual. We also show that each of the two kinds of revised inconsistency measures can be considered as a particular Shapley Inconsistency Value, and can be axiomatically characterized by the corresponding revised axioms presented in this paper.  相似文献   

19.
A MAC policy framework for multilevel relational databases   总被引:1,自引:0,他引:1  
We develop a formal framework of MAC policies in multilevel relational databases. We identify the important components of MAC policies and their desirable properties. The framework provides a basis for systematically specifying MAC policies and characterizing their potential mismatches. Based on the framework, we compare and unify the MAC policies and policy components that are proposed in the literature or imposed in existing systems. Our framework could be used to capture and resolve MAC policy mismatches in the trusted interoperation of heterogeneous multilevel relational databases  相似文献   

20.
This article presents a framework developed for accomodating various object migrations in ‘statically-typed’ object databases. Requirements for supporting object migrations are stipulated, and a conceptual model for describing and facilitating different kinds of migrations is described. Associated issues of controlling such migrations are then addressed, along with an initial investigation on the interence of implied migration paths and the completeness of migration operators. Some guidelines are then given to help users conduct migrations more effectively. An implementation prototype on top of an object-oriented database system was built, which embodies full support of all migration types specified in the migration model.  相似文献   

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