The OPS Family of Production System Languages

Production systems are widely used for the development of expert systems. The OPS family of languages comprise a set of low-level production system interpreters suitable for a large class of problem domains. They provide maximum flexibility at the expense of high-level functionality such as explanation and knowledge acquisition facilities. The languages differ with respect to their expressive power and efficiency. A description of the evolution of the languages together with an analysis of their differences provides insight into the current state of the art of production system language design. While none of the languages is clearly superior to the others, it is conceivable to combine the best features of each language in a future implementation

Circuit Minimization Techniques Applied to Knowledge Engineering

Often knowledge engineers encounter situations during the interviewing process in which experts have difficulty expressing the knowledge to be captured. In these situations, the experts cannot readily present their knowledge so that the knowledge engineers can encode it in the chosen formalism (for example, in production rules). During the development of an expert system for underwriting homeowner insurance policies, this situation was occasionally encountered. When the experts could not express their knowledge in chunks suitable for encoding directly in production rules, circuit minimization techniques were used to construct the set of production rules from exhaustive tables of acquired knowledge. The techniques also served to find errors in the acquired knowledge. Circuit minimization techniques, therefore, have been found to provide valuable assistance in the knowledge engineering process, both in the acquisition and verification of knowledge

A Methodology for Programming Production Systems and its Implications on Parallelism

Production systems have been studied as a language for artificial intelligence programming for over a decade. The flexibility of a programming paradigm which allows for loosely structured, independent rules to represent knowledge is attractive. Unfortunately, two seemingly independent phenomena have hindered the ability to take full advantage of production systems. First, the performance of large production systems suffers due to the large amounts of computation required to run them. Second, the programming styles of individuals primarily accustomed to conventional programming has adversely affected the maintainability and performance of the resulting systems. The parallel execution of production systems has been studied in order to address the performance issues. Preliminary results have been interpreted pessimistically; production systems have been observed to contain only moderate to low levels of parallelism. By investigating the issue of programming style, however, it will be shown that the apparent lack of large-scale or massive parallelism is an artifact of this problem. Indeed, a set of programming guidelines and tools will be presented which yield more maintainable, understandable, and parallelizable production systems. Is there a programming methodology or environment which will allow for the development of more maintainable and parallelizable production systems? This work will attempt to demonstrate that using a combination of several techniques, resulting production systems will more appropriately conform with the theory which supports their use. Production systems are not appropriate for encoding all problem solving tasks. They are appropriate when there is a clear separation of explicit control knowledge, tabular knowledge, and pattern-directed knowledge. This classification has been presented by many researchers in the field, often in order to advocate their separation. The issue has been addressed from a knowledge representation standpoint: here it will be one of several issues which, when addressed properly, will result in systems with improved performance in addition to their more adequate representation of the knowledge. Substantially more paral1elism can be extracted from these systems. In this regard, the techniques complement parallel match algorithms which provide the first step in the solution for mapping production systems onto parallel architectures. The techniques are table-driven rules, creating constrained copies of culprit rules, multiple rule firing, and combining rule chains. These methods are combined into a new way of viewing production system execution. Rather than assuming the sequentiality of production systems and trying to extract parallelism explicitly, the systems are assumed to be implicitly parallel and all necessarily sequential aspects are explicitly defined

Liver dysfunction in children with community-acquired pneumonia: the role of infectious and inflammatory markers

Markers of infectious-inflammatory process were studied by determining the levels of pro-inflammatory cytokines - interleukin (IL) 1 and IL-6 and proteins of the acute phase of inflammation - C-reactive protein (CRP) and fibrinogen in the serum of children with community-acquired pneumonia.  It was found that the course of community-acquired pneumonia is accompanied by an increase in serum concentrations of IL-1 and IL-6 in children in parallel with the disease severity. The synthesis of pro-inflammatory cytokines stimulates the production of acute CRP, but reduces the concentration of fibrinogen in the serum of sick children. The revealed connections between the content of the studied cytokines at the systemic level and multidirectional changes in the indicators of the acute phase of inflammation indicate a violation of the liver, where proteins are synthesized in the study. It is shown that with increasing severity of pneumonia, the enzyme activity of aminotransferases - alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the serum of children increases with a simultaneous decrease in the de Ritis coefficient, indicating "hepatic" genesis. High levels of aminotransferase is closely correlated with the activity of the infectious-inflammatory process, as indicated by the positive correlation between the level of IL-1 and ALT (r = 0.047) and AST (r = 0.111). At the same time, there is a negative correlation between the levels of IL-1, CRP and the activity of aminotransferases in blood serum

Improving Production System Performance on Parallel Architectures by Creating Constrained Copies of Rules

Production systems have pessimistically been hypothesized to contain only minimal amounts of parallelism [Gupta 1984]. However, techniques are being investigated to extract more parallelism from existing systems. Among these methods, it is desirable to find those which balance the work being performed in parallel evenly among the rules, while at the same time decrease the amount of work which must be performed sequentially in each cycle. The technique of creating constrained copies of culprit rules accomplishes both of the above goals. Production systems are plagued by occasional rules which slow down the entire execution. These rules require much more processing than others and thus cause other processors to idle while the culprit rules continue to match. By creating the constrained copies and distributing them to their own processors, each performs less work while others are busy, yielding increased parallelism, improved load balancing, and less work overall per cycle

Table-driven Rules in Expert Systems

The structure and organization of expert systems can be usefully modeled after corresponding human experts. Often this modeling degrades because of insufficient expressive power in production system languages. Relational table techniques provide additional abstraction capabilities and are useful in extending the expressiveness of production system rules; the resulting systems can be easier to build, understand and debug because they can reflect more accurately human methods of reasoning. The number of superfluous rules is reduced by organizing much of the problem domain knowledge in relations in working memory. The relational table methods also provide a tool for the interfacing of knowledge bases and databases

Linear-quadratic fractional Gaussian control

This is the published version, also available here: http://dx.doi.org/10.1137/120877283.In this paper a control problem for a linear stochastic system driven by a noise process that is an arbitrary zero mean, square integrable stochastic process with continuous sample paths and a cost functional that is quadratic in the system state and the control is solved. An optimal control is given explicitly as the sum of the well-known linear feedback control for the associated deterministic linear-quadratic control problem and the prediction of the response of a system to the future noise process. The optimal cost is also given. The special case of a noise process that is an arbitrary standard fractional Brownian motion is noted explicitly with an explicit expression for the prediction of the future response of a system to the noise process that is used the optimal control

A membrane model for cytosolic calcium oscillations. A study using Xenopus oocytes

Cytosolic calcium oscillations occur in a wide variety of cells and are involved in different cellular functions. We describe these calcium oscillations by a mathematical model based on the putative electrophysiological properties of the endoplasmic reticulum (ER) membrane. The salient features of our membrane model are calcium-dependent calcium channels and calcium pumps in the ER membrane, constant entry of calcium into the cytosol, calcium dependent removal from the cytosol, and buffering by cytoplasmic calcium binding proteins. Numerical integration of the model allows us to study the fluctuations in the cytosolic calcium concentration, the ER membrane potential, and the concentration of free calcium binding sites on a calcium binding protein. The model demonstrates the physiological features necessary for calcium oscillations and suggests that the level of calcium flux into the cytosol controls the frequency and amplitude of oscillations. The model also suggests that the level of buffering affects the frequency and amplitude of the oscillations. The model is supported by experiments indirectly measuring cytosolic calcium by calcium-induced chloride currents in Xenopus oocytes as well as cytosolic calcium oscillations observed in other preparations