基于Rough表达的时态关系代数

现实世界的信息是和时间紧密相关的,因而记录和处理信息的数据库系统应该对时态问题进行考虑,以便更有效地解决现实问题;另一方面,现实世界的某些属性又很难用属性值简单描述。首先是用Rough理论对属性值进行一种刻画,用二元数组来表达属性值,并且将这种属性值的表达方式推广到一般情形,而后从时态映射的观点描述时态元组和时态关系,并由此形式描述相应的时态关系运算,从而建立了一套时态关系代数体系。     

Adding time dimension to relational model and extending relational algebra

A methodology for adding the time dimension to the relational model is proposed and relational algebra is extended for this purpose. We propose time-stamping attributes instead of adding time to tuples. Each attribute value is stored along with a time interval over which it is valid. Non-first normal form realations are used. A relation can have atomic, set-valued, triplet-valued, or set triplet-valued attributes. The last two types of attributes preserve the time (history). Furthermore, new algebraic operations are defined to extract information from historical relations. These operations convert one attribute type to another and do selection over the time dimension. Algebraic rules and identities for the new operations are also included.     

基于关系代数的XML数据查询

XML渐已成为Web上数据表示和交换的通用语言。为了有效地利用大量的XML文档,需要研究XML数据查询技术。提出了基于关系代数的XML数据查询方法。XML子句可以用关系代数表达式表示,并通过关系代数操作得到查询结果。该方法为查询XML数据提供了一种简洁和有效的手段。     

Extending the relational model to deal with probabilistic data

According to the soundness and completeness of information in databases,the expressive form and the semantics of incomplete information are discussed in this paper.On the basis of the discussion,the current studies on incomplete data in relational databases are reviewed.In order to represent stochastic uncertainty in most general sense in the real world,probabilistic data are introduced into relational databases.An extended relational data model is presented to express and manipulate probabilistic data and the operations in relational algebra based on the extended model are defined in this paper.     

A data model and algebra for probabilistic complex values

We present a probabilistic data model for complex values. More precisely, we introduce probabilistic complex value relations, which combine the concept of probabilistic relations with the idea of complex values in a uniform framework. We elaborate a model-theoretic definition of probabilistic combination strategies, which has a rigorous foundation on probability theory. We then define an algebra for querying database instances, which comprises the operations of selection, projection, renaming, join, Cartesian product, union, intersection, and difference. We prove that our data model and algebra for probabilistic complex values generalizes the classical relational data model and algebra. Moreover, we show that under certain assumptions, all our algebraic operations are tractable. We finally show that most of the query equivalences of classical relational algebra carry over to our algebra on probabilistic complex value relations. Hence, query optimization techniques for classical relational algebra can easily be applied to optimize queries on probabilistic complex value relations.     

关系数据的中心权重模糊聚类算法

k中心点算法仅仅用一个点去代表整个类显然是不足的,这必然会影响聚类结果的准确性。因此提出了一种关系数据的中心权重模糊聚类算法,在该算法中给每一个属于这个类的对象赋予一个中心权重以此来表示其作为这个类的代表对象的可能性程度,这种机制使类中的多个对象来代表整个类而不是利用类中的一个对象来代表整个类。实验结果表明,该算法能更好地发现数据集中潜在的内部结构及对象之间的关系,得到每个聚类结果更加准确的描述。     

基于BCDM的含有变量的双时态关系代数研究*

在BCDM(双时态概念数据模型)中,时间变元Now和UC的存在解决了时态记录的频繁更新问题;但是时态变元的存在又给数据库的操作带来某种不确定性甚至是错误,同时引起关系代数运算的歧义。基于BCDM,通过绑定时间变元,用时态映射的集合定义时态关系,由此建立了一种含有时间变元的双时态关系代数体系。该关系代数体系在双时态运算下是封闭的。     

模糊灰关联在QAR故障数据检测中的应用

针对传统的灰色关联故障诊断算法无法解决大样本数据的问题,提出一种基于模糊分割灰关联的QAR（quick ac‐cess recorder）故障数据检测算法。鉴于QAR数据是数据结构复杂、维数高的时间序列数据,利用模糊分割将QAR数据分割成不重叠的子序列,从中提取出待检测故障序列,计算待检测序列与标准序列间的灰关联度,根据最大关联度原则进行故障模式识别并确定诊断结果。仿真结果表明,该算法的预测结果与实际情况基本一致,具有简单可靠、诊断精度高等优点。     

XML形式数据模型及其查询代数

提出了XML的形式数据模型及其查询代数,主要包括以下几个方面：构造先后序关系、引入带根连通有向图、建立XML形式数据模型(XFDM)和XML查询代数(XFQA)。它形成了一个较为完整的XML数据库管理系统的理论基础,可以作为XML以及其它半结构化数据库管理系统查询存储、查询分解、查询优化和查询实现的形式化基础。     

数据质量模型及选择运算中的质量传播研究

针对数据库数据质量评价问题,给出了一个属性粒度的质量评价模型,定义了正确性评价指标。在分析量化前后属性错误率的基础上,给出了两种错误率之间的关系。还研究了关系代数选择运算在键属性条件下的质量传播关系,得出了选择运算前后正确性不变的结论,并分别用属性量化前后错误率进行了表示。     

Time-based operators for relational algebra query languages

We present a new approach for historical relational algebra languages based upon generalized logic for Boolean and comparison operators and a temporal modification of the standard relational algebra operators. Historical versions of standard (snapshot) relational algebra operators based upon this generalized logic are presented. The temporal modification employs a logic that operates on sets of value/time-interval pairs and which can be applied to snapshot as well as historical databases. Our emphasis is that the generalized operators can be used to enrich existing historical query languages and to provide an easier and more natural time-based interface. Using the generalized operators, users can express their queries more naturally, succinctly and elegantly. Examples are presented which illustrate that the modified operators offer a good degree of flexibility in expressing different temporal requirements.     

A functional processor for the relational algebra on a microcomputer

We have built on the U.C.S.D. P-system (running on an IBM Personal Computer) a relational algebra processor, MRDS/FS, which is extremely powerful and which supports a functional syntax for the programmer-user. The relational algebra is provided in the extended operators μ-join, σ-join, project and select. The domain algebra is fully implemented for the first time, giving operations on attributes: arithmetic, logic, comparison and four different categories of aggregation of these. A strictly functional syntax is provided, permitting user-defined functions using the relational and domain algebras as primitive operations. An interactive editor permits the creation, copying and changing of both relations and user-defined functions.     

Membership problems for data dependencies in relational expressions

In relational databases, a query can be formulated in terms of a relational algebra expression using projection, selection, restriction, cross product and union. In this paper, we consider a problem, called the membership problem, of determining whether a given dependency d is valid in a given relational expression E over a given database scheme R that is, whether every instance of the view scheme defined by E satisfies d (assuming that the underlying constraints in R are always satisfied).Consider the case where each relation scheme in R is associated with functional dependencies (FDs) as constraints, and d is an FD. Then the complement of the membership problem is NP-complete. However, if E contains no union, then the membership problem can be solved in polynomial time. Furthermore, if E contains neither a union nor a projection, then we can construct in polynomial time a cover for valid FDs in E, that is, a set of FDs which implies every valid FD in E.Consider the case where each relation scheme in R is associated with multivalued dependencies (MVDs) as well as FDs, and d is an FD or an MVD. Even if E consists of selections and cross products only, the membership problem is NP-hard. However, if E contains no union, and each relation scheme name in R occurs in E at most once, then the membership problem can be solved in polynomial time. As a corollary of this result, it can be determined in polynomial time whether a given FD or MVD is valid in $\text{R}{}_1\text{???R}{}_{\mathrm{s}}$, where R₁,…,R_s are relation schemes with FDs and MVDs, and $\text{R}{}_{\mathrm{i}}\text{?R}{}_{\mathrm{j}}$ is the natural join of R_i and R_j.     

关系代数派生算子语义表达式间等价性证明

关系代数的派生算子在关系数据库查询语言中得到了广泛应用。它们的语义有两种常见的表示方式,一种是基于原始算子的表达式,一种是基于一阶逻辑的表达式。但有关的文献资料都没有给出这两种表达式等价性的严格证明。文章尝试通过一系列等价变换,证明派生算子语义的这两种表达式间的等价性。从派生算子(主要是除算子)语义的原始算子表达式出发,根据关系代数表达式的特点,通过一步步的等价变换,得到派生算子语义的一阶逻辑表达式。所使用的变换方法能为关系代数表达式的正确性证明打下基础。     

On the expressive power of the relational algebra with partially ordered domains

Assuming data domains are partially ordered, we define the partially ordered relational algebra (PORA) by allowing the ordering predicate ? to be used in formulae of the selection operator σ. We apply Paredaens and Bancilhon's Theorem to examine the expressiveness of the PORA, and show that the PORA expresses exactly the set of all possible relations which are invariant under order-preserving automorphisms of databases. The extension is consistent with the two important extreme cases of unordered and linearly ordered domains. We also investigate the three hierarchies of: (1) computable queries, (2) query languages and (3) partially ordered domains, and show that there is a one-to-one correspondence between them.     

面向动态模糊数据的关系数据库系统的研究

为使关系数据库系统具备处理动态模糊数据的能力,将动态模糊理论和关系数据库理论相结合,通过分析面向动态模糊数据的关系数据库系统的功能,构造了该数据库的系统结构,探讨了实现该数据库的方法,对面向动态模糊数据的关系数据库系统做了初步的研究。     

OceanBase分布式关系数据库架构与技术

关系数据库是当今社会的关键信息基础设施,互联网和数字化带来了高并发和海量数据,传统关系数据库均为集中式架构,处理能力和存储容量都捉襟见肘. OceanBase分布式关系数据库基于通用PC服务器,不仅实现了在线水平伸缩,还实现了机房故障自动无损容灾以及高倍率数据压缩等,已经应用于金融、政务、通信和互联网等行业. 介绍了OceanBase分布式关系数据库的系统架构和关键技术,包括分布式事务处理、基于LSM-tree 的存储系统以及分布式SQL优化器. 详细阐述了OceanBase数据库的高可用和数据一致性,包括RPO为0和RTO小于8 s. 也介绍了OceanBase数据库多租户机制,即采用了集群内原生多租户设计,在集群内实现多个互相独立的数据库服务. 基于Sysbench和TPC-H评测基准,对比实验结果表明：1）在单机模式下,OceanBase的性能是MySQL的1.27倍至2倍多;2）在单主模式下,OceanBase的性能是MySQL的1.25倍至近2倍;3）在多主模式下,OceanBase的性能是MySQL的1.09倍至3.1倍,对于OLAP的复杂查询,OceanBase 的性能是MySQL 的6 倍到327倍.

     

FI代数上的直觉模糊滤子和同余关系

在FI代数上引入直觉模糊滤子的概念,给出了直觉模糊滤子的一个等价刻画,探讨了由直觉模糊滤子诱导的同余关系,证明了一些性质。