Aggregation and negation-as-failure

Set-grouping and aggregation are powerful operations of practical interest in database query languages. An aggregate operation is a function that maps a set to some value, e.g., the maximum or minimum in the set, the cardinality of this set, the summation of all its members, etc. Since aggregate operations are typically non-monotonic in nature, recursive programs making use of aggregate operations must be suitably restricted in order that they have a well-defined meaning. In a recent paper we showed that partial-order clauses provide a well-structured means of formulating aggregate operations with recursion. In this paper, we consider the problem of expressing partial-order programs via negation-as-failure (NF), a well-known non-monotonic operation in logic programming. We show a natural translation of partial-order programs to normal logic programs: Anycost-monotonic partial-order programsP is translated to astratified normal program such that the declarative semantics ofP is defined as the stratified semantics of the translated program. The ability to effect such a translation is significant because the resulting normal programs do not make any explicit use of theaggregation capability, yet they are concise and intuitive. The success of this translation is due to the fact that the translated program is a stratified normal program. That would not be the case for other more general classes of programs thancost-monotonic partial-order programs. We therefore develop in stages a refined translation scheme that does not require the translated programs to be stratified, but requires the use of a suitable semantics. The class of normal programs originating from this refined translation scheme is itself interesting: Every program in this class has a clear intended total model, although these programs are in general neither stratified nor call-consistent, and do not have a stable model. The partial model given by the well-founded semantics is consistent with the intended total model and the extended well founded semantics,WFS ⁺, defines the intended model. Since there is a well-defined and efficient operational semantics for partial-order programs^{14, 15, 21)} we conclude that the gap between expression of a problem and computing its solution can be reduced with the right level of notation. Mauricio J. Osorio G., Ph.D.: He is an Associate Professor in the Department of Computer Systems Engineering, University of the Americas, Puebla, Mexico. He is the Head of the Laboratory of Theoretical Computer Science of the Center of Research (CENTIA), Puebla, Mexico. His research is currently funded by CENTIA and CONACYT (Ref. #C065-E9605). He is interested in Applications of Logic to Computer Science, with special emphasis on Logic Programming. He received his B.Sc. in Computer Science from the Universidad Autonoma de Puebla, his M.Sc. in Electrical Engineering from CINVESTAV in Mexico, and his Ph.D. from the State University of New York at Buffalo in 1995. Bharat Jayaraman, Ph.D.: He is an Associate Professor in the Department of Computer Science at the State University of New York at Buffalo. He obtained his bachelors degree in Electronics from the Indian Institute of Technology, Madras in 1975, and his Ph.D. from the University of Utah in 1981. His research interests are in Programming Languages and Declarative Modeling of Complex Systems. He has published over 50 research papers. He has served on the program committees of several conferences in the area of Programming Languages, and he is presently on the Editorial Board of the Journal of Functional and Logic Programming.     

多查询之间的包含判断

以往的查询包含判断,并不是真正意义上的查询包含,而是一种被称为一致性包含的概念,一致性包含是查询包含的充分条件,而不是必要条件,而且一般的查询包含只考虑两个查询之间的包含关系,该文使用视图更新的方法判断多查询之间的包含关系,并且文章中涉及的视图更新是独立于具体方法的。在判断多查询之间的包含关系时,该文还用到了副的文字量。     

基于XML+DOM4J的数据库集成技术研究

如何实现数据库的集成、共享和利用,提高了信息系统的整体效能,以及解决了XML和数据库双向传输的瓶颈,成为信息支持系统的关键问题之一。该文在分析可扩展标记语言XML特点的基础上,对XML与数据库之间基于DOM模型的映射方式进行了探讨,并给出了以XML文件作为中间文件的异构数据库集成,以及XML文档和数据库之间数据传输的实现方法。     

A Data Model for Data Integration

Data integration systems provide a uniform query interface (UQI) to multiple, autonomous data sources [Alon Y. Halevy. Answering queries using views: A survey. The VLDB Journal, 10(4):270–294, 2001]. This paper presents the universal data model (UDM) that captures the semantically salient aspects of relational, entity-relationship, and XML data models. As a consequence, UDM — including its accompanying query language — provides a simple and elegant UQI for integrating data represented in some of the most widely adopted data models.     

Global stabilization by output feedback: examples and counterexamples

We show by means of examples that global complete observability and global stabilizability by state feedback are not sufficient to guarantee global stabilizability by dynamic output feedback. We show that a main obstruction is related to ‘unboundedness unobservability’. This is that some unmeasured state components may escape in finite time whereas the measurements remain bounded.     

SQL查询在Visual FoxPro数据库中的应用

数据查询是数据库管理系统中不可缺少的部分。该文主要介绍了SQL SELECT查询语句在Visual FoxPro中的应用以及在不同版本存在的问题和解决方法。     

Completeness, decidability and complexity of entailment for RDF Schema and a semantic extension involving the OWL vocabulary

We prove that entailment for RDF Schema (RDFS) is decidable, NP-complete, and in P if the target graph does not contain blank nodes. We show that the standard set of entailment rules for RDFS is incomplete and that this can be corrected by allowing blank nodes in predicate position.We define semantic extensions of RDFS that involve datatypes and a subset of the OWL vocabulary that includes the property-related vocabulary (e.g. FunctionalProperty), the comparisons (e.g. sameAs and differentFrom) and the value restrictions (e.g. allValuesFrom). These semantic extensions are in line with the ‘if-semantics’ of RDFS and weaker than the ‘iff-semantics’ of D-entailment and OWL (DL or Full). For these semantic extensions we present entailment rules, prove completeness results, prove that consistency is in P and that, just as for RDFS, entailment is NP-complete, and in P if the target graph does not contain blank nodes. There are no restrictions on use to obtain decidability: classes can be used as instances.     

VB中数据库通用查询程序的设计

在分析结构化查询语句的基础上，提出了在VB中实现通用动态查询程序的原理和方法，并给出了具体的程序代码。     

Reverse engineering database queries from examples: State-of-the-art,challenges, and research opportunities

With the popularization of data access and usage, an increasing number of users without expert knowledge of databases is required to perform data interactions. Often, these users face the challenges of writing and reformulating database queries, which consume a considerable amount of time and frequently yield unsatisfactory results. To facilitate this human–database interaction, researchers have investigated the Query By Example (QBE) paradigm in which database queries are (semi) automatically discovered from data examples given by users. This paradigm allows non-database experts to formulate queries without relying on complex query languages. In this context, this work aims to present a systematic review of the recent developments, open challenges, and research opportunities of the QBE reported in the literature. This work also describes strategies employed to leverage efficient example acquisition and query reverse engineering. The obtained results show that recent research developments have focused on enhancing the expressiveness of produced queries, minimizing user interaction, and enabling efficient query learning in the context of data retrieval, exploration, integration, and analytics. Our findings indicate that future research should concentrate efforts to provide innovative solutions to the challenges of improving controllability and transparency, considering diverse user preferences in the processes of learning personalized queries, ensuring data quality, and improving the support of additional SQL features and operators.     

分布式数据库中多元连接查询优化的研究

论文对分布式数据库中多元连接查询操作次序的确定问题提出了优化，通过引入收益代价比的概念，提出了一基于贪心算法的选择模型。通过该模型，可以得到理想的连接次序的选取方案。     

VB中数据库通用查询程序的设计

在分析结构化查询语句的基础上,提出了在VB中实现通用动态查询程序的原理和方法,并给出了具体的程序代码。     

Connector Colouring I: Synchronisation and Context Dependency

Reo is a coordination model based on circuit-like connectors which coordinate components through the interplay of data flow, synchronisation and mutual exclusion, state, and context-dependent behaviour. This paper proposes a scheme based on connector colouring for determining the behaviour of a Reo connector by resolving its synchronisation and exclusion constraints. Colouring a Reo connector in a specific state with given boundary conditions (I/O requests) provides a means to determine the routing alternatives for data flow. Our scheme has the advantage over previous models in that it is simpler to implement and that it models Reo connectors more closely to their envisaged semantics than existing formal models.     

时态面向对象数据库查询算法研究

时态关系数据库在关系数据库的基础上扩充了对时间数据的处理、而时态面向对象数据库则是在面向对象数据库的基础上扩充了对时间数据的处理。在时态数据基态修正模型的基础上,讨论了时态面向对象数据库查询优化策略,并给出相应的算法。     

Object query optimization through detecting independent subqueries

The problem of query optimization in object-oriented databases is addressed. We follow the Stack-Based Approach to query languages, which employs the naming-scoping-binding paradigm of programming languages rather than traditional database concepts such as relational/object algebras or calculi. The classical environment stack is a semantic basis for definitions of object query operators, such as selection, projection/navigation, dependent join, and quantifiers. We describe a general object data model and define a formalized OQL-like query language SBQL. Optimization by rewriting concerns queries containing so-called independent subqueries. It consists in detecting them and then factoring outside loops implied by query operators. The idea is based on the formal static analysis of scoping rules and binding names occurring in a query. It is more general than the classical pushing selections/projections before joins.     

关系数据库中的多表联接查询

联接查询是关系数据库中最主要的查询．本文通过实例说明关系数据库中进行多表联接查询时联接的顺序性。     

AP-I:一种快速预测路网中移动对象未来位置的索引

随着智能交通、基于位置的广告投放、移动对象监测等应用的广泛发展,如何快速预测未来某一时间点的对象的位置成为目前的一个研究热点。提出了一种新颖的AP-I(Adaptive Predication-Index)索引,其在历史轨迹数据缺乏的情况下,能够追踪移动对象的当前位置,大幅提高预测查询的运行效率。与现有的Predictive Tree[4]索引相比,AP-Index能有效地挖掘移动对象之间的路径关联性,避免大量的索引更新和重建操作,提高索引效率。同时,通过引入AP(Adaptive Probability) 以及Pruning操作,进一步减小AP-I,提高索引的命中率和查询效率。实验表明,与Predictive Tree相比,在保证同等查询效率的基础上,AP-I实现了更优的准确度、更新效率和空间效率。     

数据库的查询优化研究

在以数据库为核心的应用系统中，查询操作最为频繁，实现快速查询将直接影响数据库应用系统的性能。正确地理解和恰当地使用索引可以在数据库中实现快速的数据查询。