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1.
Weak Generalized Closed World Assumption   总被引:1,自引:0,他引:1  
Explicit representation of negative information in logic programs is not feasible in many applications such as deductive databases and artificial intelligence. Defining default rules which allow implicit inference of negated facts from positive information encoded in a logic program has been an attractive alternative to the explicit representation approach. There is, however, a difficulty associated with implicit default rules. Default rules such as the CWA and the GCWA, which closely model logical negation, are in general computationally intractable. This has led to the development of weaker definitions of negation such as the Negation-As-Failure (NF) and the Support-For-Negation (SN) rules which are computationally simpler. These are sound implementations of the CWA and the GCWA, respectively. In this paper, we define an alternative rule of negation based upon the fixpoint definition of the GCWA. This rule, called the Weak Generalized Closed World Assumption (WGCWA), is a weaker definition of the GCWA that allows us to implement a sound negation rule, called the Negation-As-Finite-Failure (NAFF), similar to the NF-rule and less cumbersome than the SN-rule. We present three definitions of the NAFF. Two declarative definitions similar to those for the NF-rule and one procedural definition based on SLI-resolution.  相似文献
2.
The computational complexity of a number of problems relating to minimal models of non-Horn deductive databases is considered. In particular, the problem of determining minimal model membership is shown to be NP-complete for non recursive propositional databases. The structure of minimal models is also examined using the notion of a cyclic tree, and methods of determining minimal model membership, minimality of models and compiling the GCWA are presented. The handling of negative premises is also considered using perfect model semantics, and methods for computing perfect model membership are presented.  相似文献
3.
姜云飞 《计算机学报》1995,18(7):517-522
本文提出了L集合的概念以及一种新的使用L集合的一阶数据库询问求值方法。因为这种方法对原数据库只增加一个新字句,所以询问求值的效率大为提高,而且因为可以直接使用L集合回答对数据库的询问,求值过程比较简单。  相似文献
4.
We present a simple and intuitive extension GCWAG of the generalized closed world assumption (GCWA) from positive disjunctive deductive databases to general disjunctive deductive databases (with default negation). This semantics is defined in terms of unfounded sets and possesses an argumentation-theoretic characterization. We also provide a top-down procedure for GCWAG, which is sound and complete with respect to GCWAG. We investigate two query evaluation methods for GCWAG: database partition, and database splitting. The basic idea of these methods is to divide the original deductive database into several smaller sub-databases and the query evaluation in the original database is transformed into the problem of query evaluation in smaller or simplified components. We prove that these two methods of query evaluation are all sound with respect to GCWAG.  相似文献
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In this paper,the relationship between argumentation and closed world reasoning for disjunctive information is studied.In particular,the authors propose a simple and intuitive generalization of the closed world assumption(CWA) for general disjunctive deductive databases(with default negation).This semantics,called DCWA,allows a natural argumentation-based interpretation and can be used to represent reasoning for disjunctive information.We compare DCWA with GCWA and prove that DCWA extends Minker‘s GCWA to the class of disjunctive databases with defacult negation.Also we compare our semantics with some related approaches.In addition,the computational complexity of DCWA is investigated.  相似文献
8.
陆汝钤  张松懋 《软件学报》2004,15(12):1751-1763
报告了关于少儿图灵测试(CTT)的一项研究工作.研究区别于其他人的主要之处是该测试程序是基于知识的,它依靠一个海量常识知识库的支持.给出了作者研究少儿图灵测试的动机、设计、技术、实验结果和平台(包括一个知识引擎和一个会话引擎).最后给出了关于少儿图灵测试的几点研究结论和思考.  相似文献
9.
王克文  周立柱  冯建华 《软件学报》2001,12(9):1265-1270
析取信息的表示是一个重要的研究问题.DCWA(析取封闭假设)为一般演绎数据库提供了一种谨慎语义,并且扩充了标准的良基语义.同时DCWA支持争论推理,为广义封闭世界假设提供了一种逼近.基于此,提出了DCWA的过程语义,并证明了它的可靠性和完备性.  相似文献
10.
The minimal entailment Min has been characterized elsewhere by where Cn is the first-order consequence operation, P is a set of clauses (indefinite deductive data base; in short: a data base), is a clause (a query), and Pos is the set of positive (that is, bodiless) ground clauses. In this paper, we address the problem of the computational feasibility of criterion (1). Our objective is to find a query evaluation algorithm that decides P Min by what we call indefinite modeling, without actually computing all ground positive consequences of P and P {}. For this purpose, we introduce the concept of minimal indefinite Herbrand model MP of P, which is defined as the set of subsumption-minimal ground positive clauses provable from P. The algorithm first computes MP by finding the least fixed-point of an indefinite consequence operator TIP. Next, the algorithm verifies whether every ground positive clause derivable from MP {} by one application of the parallel positive resolution rule (in short: the PPR rule) is subsumed by an element of MP. We prove that the PPR rule, which can derive only positive clauses, is positively complete, that is, every positive clause provable from a data base P is derivable from P by means of subsumption and finitely many applications of PPR. From this we conclude that the presented algorithm is partially correct and that it eventually halts if both P and MP are finite. Moreover, we indicate how the algorithm can be modified to handle data bases with infinite indefinite Herbrand models. This modification leads to a concept of universal model that allows for nonground clauses in its Herbrand base and appears to be a good candidate for representation of indefinite deductive data bases.  相似文献
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