KJ3—a tool assisting formal validation of knowledge-based systems

KJ3 is the first system which incorporates theorem proving techniques with the Petri Net description scheme for knowledge validation of rule based systems (RBSs). By converting the validation tasks of RBSs to reachability problems of Enhanced High-level Petri Net (EHLPN), KJ3 performs validation by proving if the hypothetical reachability problem is true. The establishment of the hypothesis corresponds to the achievement of the validation tasks. Since the properties of RBSs, such as refraction, conservation of facts, variables, closed world assumption, and negative information, can be properly represented and handled by EHLPN, different types of RBSs can be processed in KJ3. Since checking user specifications becomes investigating the reachability problems of EHLPN, all types of validation tasks can be handled by KJ3. The validation results can be directly extracted from the inference process to allow the users to explain the validation results. The inference process is mathematically traceable, sound, and complete, KJ3 guarantees that the validation outcome is reliable.

The application of a supervisory knowledge-based system (KBS) to provide robust multivariable control of a chemical reaction process with reduced conservatism is examined. The supervisory KBS is capable of monitoring the process to detect process and control system faults or deteriorating control system performance due to changes in the process behavior or operating conditions. If a fault or change in performance is detected, the KBS formulates and implements the necessary corrective action. Control loop tuning is emphasized. The underlying mechanisms are discussed and validation results, using a rigorous simulation of the chemical reactor process, are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

It is more difficult to model a discrete system than a continuous system. Recently, a great number of applications of Petri nets to the design and the analysis of discrete systems has been reported. However, a common problem in its applications is that the required computer memories and the computation times increase explosively in accordance with the increase in the number of systems components. Some methods to divide or to reduce Petri nets have been proposed to solve this problem. Although the liveness and boundedness of Petri nets are held in the divided or reduced Petri nets, the reachability problem cannot be solved by these methods.This paper proposes another method to model discrete systems by Petri nets with place invariants. A sequential control system will be described as a typical kind of discrete system, and its structural characteristics will be used in modeling. Each component of a sequential control system will be modeled by a sub‐Petri net with place invariants. There are many components in one sequential control system, but not each one is necessarily complicated. Most sub‐Petri nets do not have so many places or transitions. It is also well known that a Petri net with place invariants is bounded and can be live by placing sufficient tokens into its initial marking. Besides, the reachability problem is not so difficult to solve in a small sub‐Petri net. Further, an activating relation to combine two or more sub‐Petri nets is defined, and some rules to reduce conflicts among enabled transitions will be described for simulations.

Most of the CAE/CAD tasks are characterized as having large search spaces, because of this they have been resistive to traditional algorithmic approaches. In recent years the knowledge-based expert systems approach of Artificial Intelligence has promised a new solution. This tutorial provides: a background as to what are knowledge-based expert systems; the type of tasks where knowledge-based expert systems can be applied; and the process of building knowledge-based expert systems.

ROBUST MULTIVARIABLE CONTROL SYSTEM DESIGNS THROUGH REAL-TIME SUPERVISORY KNOWLEDGE-BASED SYSTEMS

Traditional production planning techniques are constrained by large numbers of decision variables, uncertainty in demand and time production, and non-deterministic system behaviour (intrinsic characteristics in manufacturing). This paper presents an improvement to a methodology in the area of Knowledge Based Systems (KBS) which generates automatically Constraint Satisfaction Problems (CSP), using Petri-nets (PN) to model the problem and Constraint Programming (CP) in the solution.The methodology combines the modelling power of PN to represent both manufacturing architecture and production logistics, together with the optimisation performance given by CP. While PN can represent a whole production system, CP is effective in solving large problems, especially in the area of planning. The improvement raises from the design of a more complete algorithm to calculate the transitions firings bounds, and hence to remove useless problem variables.KeywordsLogic ProgramConstraint ProgrammingConstraint Satisfaction ProblemBoolean VariableTransition FiringThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

For the past three decades, computer-aided process planning (CAPP) has attracted a large amount of research interest. A huge volume of literature has been published on this subject. Today, CAPP research faces new challenges owing to the dynamic markets and business globalisation. Thus, there is an urgent need to ascertain the current status and identify future trends of CAPP. Covering articles published on the subjects of CAPP in the past 10 years or so, this article aims to provide an up-to-date review of the CAPP research works, a critical analysis of journals that publish CAPP research works, and an understanding of the future direction in the field. First, general information is provided on CAPP. The past reviews are summarised. Discussions about the recent CAPP research are presented in a number of categories, i.e. feature-based technologies, knowledge-based systems, artificial neural networks, genetic algorithms, fuzzy set theory and fuzzy logic, Petri nets, agent-based technology, Internet-based technology, STEP-compliant CAPP and other emerging technologies. Research on some specific aspects of CAPP is also provided. Discussions and analysis of the methods are then presented based on the data gathered from the Elsevier's Scopus abstract and citation database. The concepts of ‘Subject Strength’ of a journal and ‘technology impact factor’ are introduced and used for discussions based on the publication data. The former is used to gauge the level of focus of a journal on a particular research subject/domain, whereas the latter is used to assess the level of impact of a particular technology, in terms of citation counts. Finally, a discussion on the future development is presented.

We study the complexity of the reachability problem for a new subclass of Petri nets called simple-circuit Petri nets, which properly contains several well known subclasses such as conflict-free, BPP, normal Petri nets and more. A new decomposition approach is applied to developing an integer linear programming formulation for characterizing the reachability sets of such Petri nets. Consequently, the reachability problem is shown to be NP-complete. The model checking problem for some temporal logics is also investigated for simple-circuit Petri nets.

We study the complexity of the reachability problem for a new subclass of Petri nets called simple-circuit Petri nets, which properly contains several well known subclasses such as conflict-free, BPP, normal Petri nets and more. A new decomposition approach is applied to developing an integer linear programming formulation for characterizing the reachability sets of such Petri nets. Consequently, the reachability problem is shown to be NP-complete. The model checking problem for some temporal logics is also investigated for simple-circuit Petri nets.

In this paper, the authors contend that the area of real estate pricing is often learned from an inefficient trial and error process. To address this problem, a knowledge-based expert system (REPRES) was developed by the authors. The knowledge base and inference engine logic of REPRES are described in the paper. Use of this expert system, in which the user is directed to the price of a given home using either a market or cost approach to pricing, should result in improved quality of real estate pricing, facilitate accumulation of further knowledge about the real estate pricing process, enhance communication between users of REPRES and customers, and assist in training individuals who are unfamiliar with the logic and knowledge base of real estate pricing. Validation results indicate REPRES has accomplished these goals. The authors conclude with a discussion of the implications of such an expert system to real estate pricing and real estate modeling research.

Petri nets play a central role in the analysis of discrete, parallel and distributed systems. Reachability problem is one of the analysis of Petri nets. This paper address the analysis of reachable marking of petri nets using invariants. We translate Petri nets as transition systems. Then, through computing vanishing ideal of sample points, we present a new approach for constructing polynomial equation invariants of Petri nets. Our approach avoids first-order quantifier elimination and cylindrical algebraic decomposition. From the preliminary experiment results, we demonstrate the feasibility of our approach.

Place/transition Petri nets are a standard model for a class of distributed systems whose reachability spaces might be infinite. One of well-studied topics is verification of safety and liveness properties in this model; despite an extensive research effort, some basic problems remain open, which is exemplified by the complexity status of the reachability problem that is still not fully clarified. The liveness problems are known to be closely related to the reachability problem, and various structural properties of nets that are related to liveness have been studied. Somewhat surprisingly, the decidability status of the problem of determining whether a net is structurally live, i.e. whether there is an initial marking for which it is live, remained open for some time; e.g. Best and Esparza (Inf Process Lett 116(6):423–427, 2016. https://doi.org/10.1016/j.ipl.2016.01.011 ) emphasize this open question. Here we show that the structural liveness problem for Petri nets is ExpSpace-hard and decidable. In particular, given a net N and a semilinear set S, it is decidable whether there is an initial marking of N for which the reachability set is included in S; this is based on results by Leroux (28th annual ACM/IEEE symposium on logic in computer science, LICS 2013, New Orleans, LA, USA, June 25–28, 2013, IEEE Computer Society, pp 23–32, 2013. https://doi.org/10.1109/LICS.2013.7 ).

There is no general useful method, except the reachability tree, to find legal firing sequences even for a bounded Petri net. An LP-based method with semi-polynomial-time-complexity for this problem with the m/spl times/1 known firing count vector u has been recently reported by Fujii et al (1994), but its disadvantage is that the size of constraints becomes exhaustive. For improving the above point, this paper proposes a DP-based method which can reduce about d/sup -1/ times the size of constraints for each subprocess and can also avoid the space explosion in DP by using some properties between a Petri net and its reversed net, where d is the length of firing sequence and is defined by d=/sup /spl Delta///spl Sigma//sub i=1//sup m/u/sub i/ and u=/sup /spl Delta//[u/sub i/]. Moreover, it is shown that each suboptimization can also be solved by LP with the polynomial time complexity. As a result of the above, this proposed method based on DP including d LPs is the algorithm with about d/sup -3/ times semi-polynomial time complexity compared with that given by Fujii et al. in which only one LP is applied to the given reachability problem.

Petri nets are known to be useful for modeling concurrent systems. Once modeled by a Petri net, the behavior of a concurrent system can be characterized by the set of all executable transition sequences, which in turn can be viewed as a language over an alphabet of symbols corresponding to the transitions of the underlying Petri net. In this paper, we study the language issue of Petri nets from a computational complexity viewpoint. We analyze the complexity of theregularity problem(i.e., the problem of determining whether a given Petri net defines an irregular language or not) for a variety of classes of Petri nets, includingconflict-free,trap-circuit,normal,sinkless,extended trap-circuit,BPP, andgeneralPetri nets. (Extended trap-circuit Petri nets are trap-circuit Petri nets augmented with a specific type ofcircuits.) As it turns out, the complexities for these Petri net classes range from NL (nondeterministic logspace), PTIME (polynomial time), and NP (nondeterministic polynomial time), to EXPSPACE (exponential space). In the process of deriving the complexity results, we develop adecomposition approachwhich, we feel, is interesting in its own right, and might have other applications to the analysis of Petri nets as well. As a by-product, an NP upper bound of the reachability problem for the class of extended trap-circuit Petri nets (which properly contains that of trap-circuit (and hence, conflict-free) and BPP-nets, and is incomparable with that of normal and sinkless Petri nets) is derived.

A formal model called database manipulating systems was introduced to model data-aware dynamic systems. Its semantics is given by an infinite labelled transition systems where a label can be an unbounded relational database. Reachability problem is undecidable over schemas consisting of either a binary relation or two unary relations. We study the reachability problem under schema restrictions and restrictions on the query language. We provide tight complexity bounds for different combinations of schema and query language, by reductions to/from standard formalism of infinite state systems such as Petri nets and counter systems. Our reductions throw light into the connections between these two seemingly unrelated models.