Improving Federated Database Queries Using Declarative Rewrite Rules for Quantified Subqueries

Transforming queries for efficient execution is particularly important in federated database systems since a more efficient execution plan can require many fewer data requests to be sent to the component databases. Also, it is important to do as much as possible of the selection and processing close to where the data are stored, making best use of facilities provided by the federation's component database management systems. In this paper we address the problem of processing complex queries including quantifiers, which have to be executed against different databases in an expanding heterogeneous federation. This is done by transforming queries within a mediator for global query improvement, and within wrappers to make the best use of the query processing capabilities of external databases. Our approach is based on pattern matching and query rewriting. We introduce a high level language for expressing rewrite rules declaratively, and demonstrate the use and flexibility of such rules in improving query performance for existentially quantified subqueries. Extensions to this language that allow generic rewrite rules to be expressed are also presented. The value of performing final transformations within a wrapper for a given remote database is shown in several examples that use AMOS II—an SQL3-like system.     

Remote Access to Multimedia Databases: An Object Oriented Approach

Recent advances in media processing technology have resulted in the generation of vast amounts of multimedia information. There exists a need to manage this information. This paper describes the design and implementation of an object-oriented system used for remote multimedia database access. The work includes the design of a framework to model multimedia information in the object-oriented database POET, the development of a POET multimedia server to provide access to this information and the design of client interfaces to the system.     

Protocols for Integrity Constraint Checking in Federated Databases

A federated database is comprised of multiple interconnected database systems that primarily operate independently but cooperate to a certain extent. Global integrity constraints can be very useful in federated databases, but the lack of global queries, global transaction mechanisms, and global concurrency control renders traditional constraint management techniques inapplicable. This paper presents a threefold contribution to integrity constraint checking in federated databases: (1) The problem of constraint checking in a federated database environment is clearly formulated. (2) A family of protocols for constraint checking is presented. (3) The differences across protocols in the family are analyzed with respect to system requirements, properties guaranteed by the protocols, and processing and communication costs. Thus, our work yields a suite of options from which a protocol can be chosen to suit the system capabilities and integrity requirements of a particular federated database environment.     

面向对象图象处理的研究

针对当前微机图象处理领域中存在的一些问题，本文提出了一种面向对象的图象处理方法，这对于解决微机图象处理中存在的问题具有一定的参考价值。     

Producing Interoperable Queries for Relational and Object-Oriented Databases

In this paper, we develop techniques to produce interoperable queries with object and relational databases. A user poses a local query in a local query language, against a local object or relational schema. We transparently produce appropriate queries with respect to a remote target object or relational schema, corresponding to some remote database which contains data relevant to the user's query. Mapping knowledge to resolve representational heterogeneities in local and remote schemas is expressed in a canonical representation, CRmapping, and is independent of the particular data model. A canonical representation CRquery is also used to resolve heterogeneities of query languages. A set of heterogeneous transformation algorithms define the appropriate transformations from the local queries to the remote queries. The use of canonical representations (CR) allows us to represent queries independent of the particular query language, and to resolve representational conflicts in a uniform manner, independent of models and query languages.     

Duality for Goal-Driven Query Processing in Disjunctive Deductive Databases

Bottom-up query-answering procedures tend to explore a much larger search space than what is strictly needed. Top-down processing methods use the query to perform a more focused search that can result in more efficient query answering. Given a disjunctive deductive database, DB, and a query, Q, we establish a strong connection between model generation and clause derivability in two different representations of DB and Q. This allows us to use a bottom-up procedure for evaluating Q against DB in a top-down fashion. The approach requires no extensive rewriting of the input theory and introduces no new predicates. Rather, it is based on a certain duality principle for interpreting logical connectives. The duality transformation is achieved by reversing the direction of implication arrows in the clauses representing both the theory and the negation of the query. The application of a generic bottom-up procedure to the transformed clause set results in top-down query answering. Under favorable conditions efficiency gains are substantial, as shown by our preliminary testing. We give the logical meaning of the duality transformation and point to the conditions and sources of improved efficiency. We show how the duality approach can be used for refined query answering by specifying the minimal conditions (weakest updates) to DB under which Q becomes derivable. This is shown to be useful for view updates in disjunctive deductive databases as well as for other interesting applications.     

基于语义相似度的Web数据库不精确查询方法

为了解决普通用户对于Web数据库的不精确查询问题,提出了一种基于语义相似度的Web数据库不精确查询方法。对于一个给定查询,该方法首先在查询历史中找出一个(或若干)与其相似度高于给定放松阈值的查询,然后从数据库中找出与这些查询相匹配的元组作为当前查询的不精确查询的结果,最后将这些查询结果按其对初始查询的满足程度进行排序。实验结果表明,提出的不同查询之间的语义相似度评估方法性能稳定、评估结果合理,不精确查询方法具有较高的查全率和排序准确性。     

Holistically Stream-based Processing Xtwig Queries

Unlike a twig query, an Xtwig query contains some selection predicates with reverse axes which are either ancestor or parent. To evaluate such queries in the stream-based context, some rewriting rules have been proposed to transform the paths with reverse axes into equivalent reverse-axis-free ones. However, the transformation method is expensive due to multiple scanning input streams and the generation of unnecessary intermediate results. To solve these problems, a holistic stream-based algorithm XtwigStack is proposed for Xtwig queries. Experiments show that XtwigStack is much more efficient than the transformation method.     

一种处理Skyline查询的有效方法

skyline查询是近年来数据库领域的一个研究重点和热点.当系统中存在多个不同维空间上的skyline查询时,现有的工作均直接从底层关系表中获取这些skyline查询的结果集.显然,当底层关系表的基数较大且skyline查询的个数较多时,现有方法的处理效率极其低下.基于此,提出一种使用预存储的n个skyline集合{PR\\-1,…,PR\\-n}来回答用户提交的m个不同维空间上的skyline查询{SQ\\-1,…,SQ\\-m}的有效方法EAPSQ(efficient algorithm for processing skyline queries).算法充分考虑预存储的skyline集合的编码机制,采用经济学中边际贡献(contribution margin)的概念,使得m个用户提交的skyline查询在n个预存储的skyline集合间的分配达到最佳状态,从而显著提高了处理用户m个skyline查询的效率.实验评估表明,EAPSQ算法具有有效性和实用性.     

Distributed Processing of Similarity Queries

Many modern applications in diverse fields demand the efficient manipulation of very large multidimensional datasets. It is evident, that efficient and effective query processing techniques need to be developed, in order to provide acceptable response times in query processing. In this paper, we study the processing of similarity nearest neighbor queries in large distributed multidimensional databases, where objects are represented as vectors in a vector space, and are distributed in a multi-computer environment. The departure from the centralized case embodies a number of advantages and (unfortunately) a number of difficulties that need to be successfully overcome. In this perspective, four query evaluation strategies are presented, namely Concurrent Processing (CP), Selective Processing (SP), Two-Phase Processing (2PP) and Probabilistic Processing (PRP). The proposed techniques are compared analytically and experimentally, in order to discover the advantages of each one, as well as the best cases where each one should be applied. Experimental results are presented, demonstrating the performance of each method under different parameters values. Also, we investigate the impact of derived data that should be maintained in order to process similarity queries efficiently.     

利用自动机高效处理XML路径表达式查询

在XML查询处理中,应用于绝大多数XML查询语言中的路径表达式在定位和查询XML数据和数据的结构关系方面具有极强的表达能力,并且由于XML数据的半结构化性,使得XML路径表达式查询的查询处理技术的研究与传统的数据库查询处理技术相比有着全新的特点和挑战.一些目前已有的查询处理技术可以用来处理路径表达式,但是查询处理中产生的大量中间结果导致了这些方法应用在大规模XML文档和复杂的路径表达式查询中时查询效率急剧下降.文中利用自动机技术设计了一个处理XML路径表达式查询的高效方法--SAM.SAM的基本思想是将路径表达式查询转化成一个与之完全等价的自动机,然后将其与从XML文档中抽象出来的模式路径相匹配.文中同时也给出了基于SAM方法的针对路径表达式中"//"操作符计算的有效解决方案.实验证明:SAM是一种非常有效的查询方法,在计算大数据量复杂路径表达式查询时具有非常高的效率,是一种实用的XML路径表达式查询方法.     

基于TPU-tree的Skyline分支定界查询算法

提出了一种新的限定性skyline查询理念,并给出了高效的处理技术。分支定界方法是当前skyline查询处理效率较高的技术之一,在一种不确定移动对象的索引策略TPU-tree之上,基于分支定界方法提出了B2CPS可限定性skyline查询处理算法。实验结果表明,提出的基于TPU-tree的B2CPS算法可以很大程度地提高限定性skyline查询的效率,在移动对象频繁更新的情况下亦能保持较高的查询性能,因此具有较好的实用价值。     

分布对象管理的联邦交易模型

分布对象管理是实现分布对象互操作的一个重点.该文通过扩展ODP中的基本交易模型,实现了对象服务的局部管理,提出了一种新的联邦交易模型,使用联邦交易空间和信任度的概念实现了大规模互操作环境中的对象服务的全局管理,给出了分布对象服务的联邦搜索过程和联邦搜索规则,以及联邦查询的最佳搜索路径选择算法,研究并提出了联邦交易的实现结构模型和建立联邦和约的协商协议.     

基于Petri网的分布式面向对象数据库系统建模

首先介绍了分布式面向对象数据库（DOODB）的基本概念，提出了以对象模型，事件模型，事务模型三个正交维来进行建模的思想，并利用面向对象（OO）技术及Petri网理论对DOODB进行了系统建模，这种建模表示方法对开发分布式数据库及其管理系统有一定的指导意义。     

基于位置的路网Skyline查询处理研究

基于位置的路网Skyline查询可根据用户的需求及用户所处的位置,从大量数据中快速返回给用户期望的数据,但已有的道路网络技术需要计算大量的路网距离及数据点间支配关系的运算,导致查询效率较低。提出一种基于路网数据点的倒排索引查询算法DSR。通过计算少量数据点的路网距离求得最终结果,减小路网距离计算的代价,从而加快数据点间支配关系的判定,提升查询效率。在此基础上,在数据点更新情况下给出算法的动态维护,仅通过维护少量数据,DSR即可以快速地计算出Skyline集合。实验结果表明,与SSI、BSS等算法相比,该算法具有较高的查询效率,且时间性能明显提升。     

Toward Automated Support for Transparent Interoperable Queries

Many Object-Oriented Databases (OODBs) use programming languages that predate Java, such as C++, CLOS and Smalltalk. Thus, there is a growing need for interoperating these OODBs with new applications that require Java. Unfortunately, there are few mechanisms that allow software developers to easily integrate Java applications with non-Java OODBs. Although various interoperability mechanisms have been developed over the years, these approaches have some significant drawbacks in practice. They are often difficult to use, provide little, if any, automated support, and produce software that is difficult to engineer and maintain. In this paper, we describe an interoperability approach that allows application developers to seamlessly and transparently access non-Java OODBs from Java applications. We first present JOQL, a Java-based object query language that we are developing. JOQL queries are embedded in Java applications and are used to perform queries over C++-based OODBs. We also describe an accompanying toolset that processes Java programs containing JOQL queries. The toolset produces all the necessary code allowing Java applications to access and manipulate a C++-based OODB. As a result, application developers are free to work in Java without having to concern themselves with the details of interoperating with C++. Finally, we provide some preliminary experimental data that demonstrates our approach incurs a reasonable performance overhead.     

Effcient Distributed Skyline Queries for Mobile Applications

In this paper, we consider skyline queries in a mobile and distributed environment, where data objects are distributed in some sites (database servers) which are interconnected through a high-speed wired network, and queries are issued by mobile units (laptop, cell phone, etc.) which access the data objects of database servers by wireless channels. The inherent properties of mobile computing environment such as mobility, limited wireless bandwidth, frequent disconnection, make skyline queries more complicat...     

Rewriting Union Queries Using Views

The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context. Although conceptually simple, our approach generalizes previous methods for finding contained rewritings of conjunctive queries and is more powerful in the sense that many rewritings that can not be found using existing methods can be found by our approach. Furthermore, implication constraints (Zhang, X., & Ozsoyoglu, Z.M. (1997). Implication and referential constraints: A new formal resaoning. IEEE TKDE, 9(6):894–910, Now/Dec.) over the base relations can be easily handled. We then present a simplified approach which is less complete, but is much faster than the general approach, and it still finds maximum rewritings in several special cases. Our general approach finds more rewritings than previous algorithms such as the Bucket and the resolution-based algorithms. Our simplified approach generalizes the U-join and the MiniCon algorithms with no loss of efficiency.