Semantic foundations of 4NF in relational database design

The issue of providing a formal justification for the use of fourth normal form (4NF) in relational database design is investigated. The motivation and formal definitions for three goals of database design are presented. These goals are the elimination of: redundancy, key-based update anomalies and fact-based replacement anomalies. It is then shown that, depending on the type of constraints permitted, either Boyce-Codd normal form (BCNF) or 4NF are the exact conditions needed to ensure most of the design goals. However, it is also shown that the conditions required to ensure the absence of a particular class of key-based update anomaly are new normal forms which have not previously been identified. In particular, for the case where the only constraints are functional dependencies (FDs), it is shown that the required normal form is a new normal form that is stronger than third normal form (3NF) yet weaker than BCNF. Similarly, in the more general case where both FD and multivalued dependencies (MVDs) are present, the required normal form is a new normal form that is weaker than 4NF. Received: 7 July 1995 / 28 December 1998     

Graphical normal forms based on root dependencies in relational data base systems

Normal forms and dependencies are an area of great current interest in the design of relational data bases. Only a subclass, namely, root dependencies and the normal forms based on them, are of direct interest to the data base designer. Dependencies outside this subclass do not have clear cut semantics and may in the long run prove to be of theoretical interest only. We have proposed the fifth normal form (5NF) to control the pattern of codependancy, the highest known root dependency. We have also shown a strong parallel between root dependencies and their normal forms and a family of hypergraphs calledS-diagrams. Graphical normal forms, based onS-diagrams have been proposed and their equivalence to conventional normal forms proved.This work was supported in part by the Science and Engineering Research Board Grant Number 214–7248.     

范式应用

从五个实例出发介绍了数据库设计的第一范式、第二范式、第三范式、BCNF范式和第四范式的定义及达到各种范式的要求.     

5G安全:通信与计算融合演进中的需求分析与架构设计

5G是未来网络空间的核心基础设施,因而5G安全是网络空间安全的重要组成部分。5G安全技术应打破以往移动通信系统成型后“打补丁式”的升级演进模式,与5G移动通信技术同步演进,实现系统安全内生与安全威胁“标本兼治”的目标。为了“有的放矢”的推动安全技术同步演进,应首先解决两个基本问题：5G安全需求是什么和5G安全体系架构是什么。针对这两个问题,本文首先从业务、网络、无线接入、用户与终端、系统五个视角梳理了5G通信与计算融合演进的技术特点,并基于这些特点系统的分析了5G安全需求;然后,面向5G安全需求,设计了5G安全总体架构;最后,总结归纳出了5G安全技术的三个发展趋势,即,“面向服务的安全”“安全虚拟化”与“增强用户隐私与数据保护”。本文希望为5G安全技术的同步演进提供有益的参考。     

关系模式规范化研究

介绍了第一、第二、第三、BCNF、第四、第五范式和域/关键字范式.     

多时间粒度约束的时态简单范式的分解

数据库逻辑设计的目的是消除数据冗余、插入和删除异常。为使时态模式满足某种范式的要求，要对时态模式进行分解，保持函数依赖和无损连接性是对算法最基本的要求。但对具有多时间粒度的时态模式进行分解时，把TBCNF作为最终目标很难实现保持函数依赖性，把T3NF作为最终目标，又很难达到规范化要求。该文提出了时态简单范式TSNF的概念及相应的分解算法，来弥补以上两点不足。     

NF-NR: A practical normal form for nested relations

We propose a normal form for nested relations, called NF-NR, which removes undesirable anomalies from a nested relational database schema. Both functional dependencies and multivalued dependencies are considered. NF-NR reduces to 3NF/4NF if the nested relation considered is actually a flat relation. Especially, NF-NR removes global redundancies among a set of nested relations. Two approaches to NF-NR database design, namely the restructuring rules approach and the ER approach, are discussed. We relate NF-NR to ER-NF, a normal form of ER defined earlier, by defining a simple mapping from an ERD in ER-NF to a set of nested relations in NF-NR. This approach effectively removes ambiguitics and redundancies on a semantic level and hence gives a set of nested relations with clean semantics and yet in good normal form. A set of desirable properties for any normal form for nested relations are described and an evaluation of several existing normal forms is given based on this set of properties. The evaluation shows that NF-NR improves over previously proposed normal forms in various aspects and is a more practical normal form for nested relations.     

基于Sentinel-2和全卷积网络的北京六环内高层建筑区提取与分析

高层建筑区是我国城镇化进程的重要标志,具有重要的社会经济功能和独特的几何形态。应用全卷积网络和Sentinel-2多光谱数据,提取北京六环内高层建筑区,并结合环线、乡镇边界和轨道交通数据,对高层建筑区的空间分布和交通可达性进行分析。结果表明：实验提出的全卷积网络方法能够实现北京高层建筑区快速精确提取,总体精度90%以上;六环内高层建筑区总面积约为192 km²,其中,二环到四环之间分布最为密集且相对均匀,密度明显高于其他环带,二环内以及四环到五环之间相较次之,五环到六环之间密度最小;六环内街道乡镇的高层建筑区分布呈现明显片状聚集特点,密度最大的区域在崇文门外、东花市和建国门外等街道,其次是金融街街道、中关村街道和望京开发街道等区域,而靠近六环的街道乡镇和故宫附近街道的高层建筑区密度较小。轨道交通可达性与高层建筑区的空间分布存在明显相关性,交通可达性越差的区域,高层建筑区越少,地铁站点1 km范围内面积约为92.62 km²,而6 km外的面积只有2.04 km²。研究结果为北京城市建设和生态景观保护提供一个新的指标参考。     

全面解析1NF及其有效性的实例论证

关系型数据库的范式理论中的1NF是目前唯一无法严格定义的范式,而其他所有范式均以符合1NF为前提.国内教育领域和软件行业,对关系型数据库设计的范式理论中的第一范式的理解和运用普遍存在偏差,全面正确理解并满足1NF对设计高性能的数据库应用程序至关重要.首先给出对1NF多层面的理解并给出其有效性的一般论证,然后通过一个实例对符合1NF和不符合1NF两种设计进行各个方面的完整比较,进一步论证全面理解1NF,并使数据库设计真正符合1NF对完成更高性能的设计具有重要意义.     

一种理性的数据库模式设计方法--范式方法

介绍了一种理论性较强的数据库模式设计方法———范式方法。范式方法基于函数依赖及范式理论。最终的数据库模式必须满足BCNF模式集或3NF模式集、无损联接和保持函数依赖这三个特性才是一个可用的数据库,才不会出现各种操作异常(插入、删除)并且能大大地减少数据冗余。     

Efficient Jarratt-like methods for solving systems of nonlinear equations

We present the iterative methods of fourth and sixth order convergence for solving systems of nonlinear equations. Fourth order method is composed of two Jarratt-like steps and requires the evaluations of one function, two first derivatives and one matrix inversion in each iteration. Sixth order method is the composition of three Jarratt-like steps of which the first two steps are that of the proposed fourth order scheme and requires one extra function evaluation in addition to the evaluations of fourth order method. Computational efficiency in its general form is discussed. A comparison between the efficiencies of proposed techniques with existing methods of similar nature is made. The performance is tested through numerical examples. Moreover, theoretical results concerning order of convergence and computational efficiency are confirmed in the examples. It is shown that the present methods are more efficient than their existing counterparts, particularly when applied to the large systems of equations.     

具有多时间粒度的时态多值依赖及时态模式分解方法研究

一个好的数据库逻辑设计目标是消除数据冗余以及插入、删除和更新异常.对于时态数据库,通过具有多时间粒度的时态函数依赖约束对时态数据库进行规范化已有大量研究.基于时态函数依赖和多值依赖理论提出了多时间粒度约束的时态多值依赖(TMVD)等概念,并给出了时态多值依赖的推理规则,对其有效性、完备性进行了证明.由于包含有限个TMVD的TMVD集通常蕴含着无限个TMVD,给出了TMVD的有限推理规则,对其有效性、完备性进行了证明.最后,基于时态多值依赖集提出了时态第四范式,并给出了时态模式的T4NF的无损分解算法,对算法的可终止性、正确性进行了证明,并对时间复杂度进行了分析.     

Multiparty Authentication Services and Key Agreement Protocols with Semi-Trusted Third Party

This paper introduces a new family of group key establishment protocols suitable for small or medium-sized groups.Five protocols are presented,using a semi-trusted server,with varying security service,The first one is a non-authenticated key agreement protocol suitable for applications with low security requirements.The second protocol adds an authenticated key agreement to provide collaborative authentication.The third and the fourth protocols provide key establishment with integrity and confirmation services,and the fifth protocol is the member adding protocol.A major advantage of the protocols is that they reduce the numbers of rouds from n to 5.     

Statistical relational databases: normal forms

Problems associated with defining normal forms of relational tables relevant to statistical processing are discussed. The concepts of derived identifier, class identifier, derived class-counts, count domains, compact domains, and uniform domains for statistical relational tables are introduced. The structures of the first and the second statistical-normal forms and the relational decompositions needed to achieve them are also discussed. It is shown that the statistical-normal form can be an important method to determine whether the usual statistical analysis techniques are valid. Some suggestions are presented for extending the structured query language (SQL) statements to achieve these operations on statistical relational tables. Some results linking Codd's normal forms with statistical normal forms are discussed. Relational statistical abnormalities, called outlyers, are also discussed     

Generalized normal form for rewriting P systems

P systems, introduced by Gh. Păun [9] as a new theoretical model for molecular computations, are based on the notion of membrane structure. Several variants of P systems have been proposed and shown to be computationally universal. One of such variant is the rewriting P systems, where we consider string-objects and process them using rewriting rules. Particular cases of normal forms for rewriting P systems were proposed in [11–13]. In this work we introduce the generalized normal form for rewriting P systems which take into consideration the depth of the membrane structure and the number of rewriting rules present in each membrane. Such generalized normal forms are given for rewriting P systems with priorities, and for partially parallel rewriting P systems. In this way, several results from the literature are generalized and improved. Received: 14 March 2002 / 5 June 2002     

Comparing Curried and Uncurried Rewriting

Currying is a transformation of term rewrite systems which may contain symbols of arbitrary arity into systems which contain only nullary symbols, together with a single binary symbol called application. We show that for all term rewrite systems (whether orthogonal or not) the following properties are preserved by this transformation: strong normalization, weak normalization, weak Church-Rosser, completeness, semi-completeness, and the non-convertibility of distinct normal forms. Under the condition of left-linearity we show preservation of the properties NF (if a term is reducible to a normal form,then its reducts are all reducible to the same normal form) and UN→ (a term is reducible to at most one normal form).We exhibit counterexamples to the preservation of NF and UN→ for non-left-linear systems.The results extend to partial currying(where some subset of the symbols are curried),and imply some modularity properties for unions of applicative systems.     

Evolution of data management

Computers can now store all forms of information: records, documents, images, sound recordings, videos, scientific data, and many new data formats. Society has made great strides in capturing, storing, managing, analyzing, and visualizing this data. These tasks are generically called data management. This article sketches the evolution of data management systems. There have been six distinct phases in data management. Initially, data was manually processed. The next step used punched-card equipment and electromechanical machines to sort and tabulate millions of records. The third phase stored data on magnetic tape and used stored-program computers to perform batch processing on sequential files. The fourth phase introduced the concept of a database schema and on-line navigational access to the data. The fifth step automated access to relational databases and added distributed and client server processing. We are now in the early stages of sixth-generation systems that store richer data types, notably documents, images, voice, and video data. These sixth-generation systems are the storage engines for the emerging Internet and intranets. Early data management systems automated traditional information processing. Today they allow fast, reliable, and secure access to globally distributed data. Tomorrow's systems will access and summarize richer forms of data. It is argued that multimedia databases will be a cornerstone of cyberspace     

A comparative study of various nested normal forms

As object-relational databases (ORDBs) become popular in the industry, it is important for database designers to produce database schemes with good properties in these new kinds of databases. One distinguishing feature of an ORDB is that its tables may not be in first normal form. Hence, ORDBs may contain nested relations along with other collection types. To help the design process of an ORDB, several normal forms for nested relations have recently been defined, and some of them are called nested normal forms. In this paper, we investigate four nested normal forms, which are NNF [20], NNF [21], NNF [23], and NNF [25], with respect to generalizing 4NF and BCNF, reducing redundant data values, and design flexibility. Another major contribution of this paper is that we provide an improved algorithm that generates nested relation schemes in NNF [20] from an a-acyclic database scheme, which is the most general type of acyclic database schemes. After presenting the algorithm for NNF [20], the algorithms of all of the four nested normal forms and the nested database schemes that they generate are compared. We discovered that when the given set of MVDs is not conflict-free, NNF [20] is inferior to the other three nested normal forms in reducing redundant data values. However, in all of the other cases considered in this paper, NNF [20] is at least as good as all of the other three nested normal forms     

LTI ODE-valued neural networks

A dynamical version of the classical McCulloch & Pitts’ neural model is introduced in this paper. In this new approach, artificial neurons are characterized by: i) inputs in the form of differentiable continuous-time signals, ii) linear time-invariant ordinary differential equations (LTI ODE) for connection weights, and iii) activation functions evaluated in the frequency domain. It will be shown that this new characterization of the constitutive nodes in an artificial neural network, namely LTI ODE-valued neural network (LTI ODEVNN), allows solving multiple problems at the same time using a single neural structure. Moreover, it is demonstrated that LTI ODEVNNs can be interpreted as complex-valued neural networks (CVNNs). Hence, research on this topic can be applied in a straightforward form. Standard boolean functions are implemented to illustrate the operation of LTI ODEVNNs. Concluding the paper, several future research lines are highlighted, including the need for developing learning algorithms for the newly introduced LTI ODEVNNs.     

Investigating a domain-key scheme of a relational database

A new approach to the synthesis of the domain-key normal form (DK/NF) for an arbitrary domain is used to analyze some criticized publications. A detailed comparison between various anomalies in database schemas, between different approaches to the design of schemas, and between the framework design method and classical and new design methods is made. The coincidence with the results of other studies is shown to be a subsequence of the strict soundness of the method proposed.