共查询到20条相似文献,搜索用时 93 毫秒
1.
2.
本文使用概念图为数据库的推理问题建立了相关的解决模型,给出了推理相关的知识 表示及推理过程的描述,建立了相关的推理控制系统。 相似文献
3.
概念格的内涵缩减与数据库推理依赖 总被引:1,自引:0,他引:1
值依赖是数据库推理问题研究的一个新课题.首先介绍了形式背景和概念格,提出了值依赖的形式概念模型.将数据属性的安全敏感级别引入到值依赖研究中,提出推理依赖及α极大推理依赖概念,并建立了形式概念格的内涵缩减与数据库推理依赖之间的关系.进一步证明了由概念格的内涵缩减推导出数据库中完备的、无冗余的α极大推理依赖集.最后提出并实例验证了发现数据库中全部推理依赖集的算法.推理依赖是关系数据库中最重要的属性依赖关系之一,其研究对检测和消除数据库推理通道具有十分重要的意义. 相似文献
4.
5.
6.
基于粗糙集理论对推理通道问题进行了研究。通过采用属性约简和属性值约简方法对数据库中的数据进行处理。在属性值约简基础之上,采用一种改进算法找出了数据库中推理规则集。进一步,将推理规则集中属性频率高的属性安全级别提高至决策属性的安全级别,从而消除推理通道。最后通过一个实例表明提出的消除通道算法是有效的。 相似文献
7.
数据库弱函数依赖推理规则挖掘方法 总被引:1,自引:0,他引:1
数据库推理问题是数据库安全研究的重要分支方向,推理通道的分析是解决推理问题的基础.传统推理规则无法处理不完全符合函数依赖的数据关系,针对这一问题,本文提出了弱函数依赖的概念,并给出了弱函数依赖的推理能力评价标准,最后给出了从数据中挖掘弱函数依赖关系的算法. 相似文献
8.
演绎数据库是将推理机制引入传统关系数据库而生成的一种新型数据库形式,它是数据库领域中一个比较新的方向。实现演绎数据库的主要问题是推理规则的表示和推理过程的实现。其中,演绎推理的有效实现是演绎数据库实现的关键。目前,实现演绎数据库的途径有两个:一个是直接用逻辑程序设计语言PROLOG来实现;另一个是在传统关系数据库 相似文献
9.
10.
一种基于粗糙集的多级安全数据库推理问题的量化分析方法 总被引:1,自引:0,他引:1
信息大都存放在数据库中,信息安全很大程度上依赖数据库的安全。推理是从已知的信息推出新的信息,它是对数据库安全的一个重要威胁,特别数据挖掘的发展,这个威胁变得更加严重。简单描述了多级安全数据库系统的推理问题;介绍了粗糙集理论的相关概念;利用粗糙集理论提出了一种对推理风险进行量化的方法,它不依赖系统安全员的知识,能够处理确定性和非确定性的推理通道;并给出了一个分析例子。 相似文献
11.
12.
13.
The logical conditioning inference problem is studied when a simple condition setting a threshold for a potential observation of a scalar observable uncertain quantity is introduced as an additional information to the pieces of evidence originally available to make inference, which include observational data. Two alternative ways of incorporating this condition can be considered. They lead to two conditioned evidences from which it is possible to start and, consequently, two different inference problems arise. Due to the need to coherently represent observational data and to express unambiguously the given evidences, these problems are formalized in a plausible logic language with observational data, within the logical probability framework. They are solved by applying the relative entropy method with fractile constraints. A comparison of the solutions obtained indicates that one of them is a particular instance of the other. It is concluded that the broadest one constitutes the general solution to the logical conditioning inference problem. 相似文献
14.
Paola Bonizzoni 《Algorithmica》2007,48(3):267-285
The inference of evolutionary trees from binary species-character matrices is a fundamental computational problem in classical
phylogenetic studies. Several problems arising in this field lead to different variants of the inference problem; some of
these concern input data with missing values or incomplete matrices. A model of inference from incomplete data that has recently
gained a remarkable interest is the Perfect Phylogeny Haplotype problem (PPH) introduced in [1] and successfully applied to
infer haplotypes from genotype data. A stated open issue in this research field is the linear-time solution of this inference
problem. In this paper we solve this question and give an O(nm)-time algorithm to complete matrices of n rows and m columns
to represent PPH solutions: we show that solving the problem requires recognizing special posets of width 2. 相似文献
15.
16.
17.
Abstract: In generating a suitable fuzzy classifier system, significant effort is often placed on the determination and the fine tuning of the fuzzy sets. However, in such systems little thought is given to the way in which membership functions are combined within the fuzzy rules. Often traditional fuzzy inference strategies are used which consequently provide no control over how strongly or weakly the inference is applied within these rules. Furthermore such strategies will allow no interaction between grades of membership. A number of theoretical fuzzy inference operators have been proposed for both regression and classification problems but they have not been investigated in the context of real-world applications. In this paper we propose a novel genetic algorithm framework for optimizing the strength of fuzzy inference operators concurrently with the tuning of membership functions for a given fuzzy classifier system. Each fuzzy system is generated using two well-established decision tree algorithms: C4.5 and CHAID. This will enable both classification and regression problems to be addressed within the framework. Each solution generated by the genetic algorithm will produce a set of fuzzy membership functions and also determine how strongly the inference will be applied within each fuzzy rule. We investigate several theoretical proven fuzzy inference techniques (T-norms) in the context of both classification and regression problems. The methodology proposed is applied to a number of real-world data sets in order to determine the effects of the simultaneous tuning of membership functions and inference parameters on the accuracy and robustness of fuzzy classifiers. 相似文献
18.
19.
Wizard: a database inference analysis and detection system 总被引:1,自引:0,他引:1
The database inference problem is a well-known problem in database security and information system security in general. In order to prevent an adversary from inferring classified information from combinations of unclassified information, a database inference analyst must be able to detect and prevent possible inferences. Detecting database inference problems at database design time provides great power in reducing problems over the lifetime of a database. We have developed and constructed a system called Wizard to analyze databases for their inference problems. The system takes as input a database schema, its constituent instances (if available) and additional human-supplied domain information, and provides a set of associations between entities and/or activities that can be grouped by their potential severity of inference vulnerability. A knowledge acquisition process called microanalysis permits semantic knowledge of a database to be incorporated into the analysis using conceptual graphs. These graphs are then analyzed with respect to inference-relevant domains we call facets using tools we have developed. We can determine inference problems within single facets as well as some inference problems between two or more facets. The architecture of the system is meant to be general so that further refinements of inference information subdomains can be easily incorporated into the system 相似文献
20.
Description logics with aggregates and concrete domains 总被引:4,自引:0,他引:4