Lipski's approach to incomplete information data bases restated and generalized in the setting of Zadeh's possibility theory

The main purpose of this paper is to make clear the connection between Lipski's approach to incomplete information databases and Zadeh's possibility theory which both appeared recently, quite simultaneously, but in different contexts. Lipski's approach is extended by introducing [0, 1]-valued levels of possibility in order to take into account the fact that our incomplete knowledge about properties of objects in databases may be based on soft (non-binary) information or on statistical-like data. Moreover, possibility theory, enlarged by the introduction of the concept of necessity, seems easier to manipulate than the semantics of usual modal logic used by Lipski. The problems of dependencies, of “yes-no” queries or of queries involving the cardinalities of specified sets when available information is incomplete are considered. Two illustrative examples are dealt with.     

State-space approach to non-linear model reference adaptive control

A new method is developed for tracking in non-linear delay-differential systems when the exact knowledge of the system parameters are not known. The method is based on securing the stability in the state spaces of plant and reference models. The results obtained are quite general in nature and can be applied to many physical systems.     

A new approach to model reference adaptive control

In classical model reference adaptive control, the goal is to design a controller to make the closed-loop system act like a prespecified reference model in the face of significant plant uncertainty. Typically, the controller consists of an identifier (or tuner) which is used to adjust the parameters of a linear time-invariant (LTI) compensator, and under suitable assumptions on the plant model uncertainty it is proven that asymptotic matching is achieved. However, the controller is typically highly nonlinear, and the closed loop system can exhibit undesirable behavior, such as large transients or a large control signal, especially if the initial parameter estimates are poor. Furthermore, its ability to tolerate time-varying parameters is typically limited. Here, we propose an alternative approach. Rather than estimating the plant or compensator parameters, instead we estimate what the control signal would be if the plant parameters and plant state were known and the "ideal LTI compensator" were applied. We end up with a linear periodic controller. Our assumptions are reasonably natural extensions of the classical ones to the time-varying setting; we allow rapid parameter variations, although we add a compactness requirement. We prove that we can obtain arbitrarily good tracking, explore the benefits and limitations of the approach, and provide a simulation study.     

An analysis of Forrester's world dynamics model

The World Dynamics model proposed by Forrester is analysed by total linearisation for the 1970 situation. It reveals the main structure of the model for a certain period of time around 1970. This structure has been verified by means of the original Forrester model, and a number of interesting conclusions about this model are drawn.     

Auditing the network environment at a technical level: Why's,how's and aha!'s

One of the pervasive concerns in dealing with cyber-security is the dreaded information systems (IS) audit. Most companies of a goodly size have an IS audit staff and if you work for a financial organization like a bank, you can count on regular visits by the populus thereof. We have all been indoctrinated to the necessity of IS audits and if you have ever worked for a larger company, you have been through them more than once — usually with mixed results, some good, some bad, some you are not terribly sure about. I have seen the entire gamut of IS audit results in my career and, unfortunately, when it comes to network security audits, most are on the “we're not sure how to really find the right data and therefore did a lame job and the networking geeks know it and are laughing at us” end of the spectrum.     

Economy of description by parsers,DPDA's,and PDA's

It is shown that there is a sequence of languages E₁, E₂,… such that every correct prefix parser (one which detects errors at the earliest possible moment, e.g., LR or LL parsers) for E_n has size 2^cn, yet a deterministic PDA recognizing E_n exists and has size O(n²). There is another easily described sequence of languages N₁, N₂,… for which N has a nondeterministic PDA of size O(n²), but no deterministic PDA of size less than 2^cn. It is shown moreover, that this latter gap can be made arbitrarily large for different sequences of languages.     

Grish's page

Grish's Home page (www.unm.edu/at dave/) is a novel introduction to the world of security-related Web pages. Not only is it entertaining and imaginative, it is extremely useful and informative. It has links to many other valuable sites, thus acting as a conduit to numerous aspects of computer security and ethics. The site is administered by David D. Grisham, the Security Administrator of Computer and Information Resources Technology (CIRT) at the University of New Mexico.     

Cisco's SAFE

Cisco Systems recently unveiled its security strategy called, SAFE, a flexible blueprint that specifies security design, implementation and management processes for companies participating in E-Business.     

Devil's advocate

In this article we will be taking a close look at SATAN; its history, what it does, how to use it safely, how to detect its use and how to fix the holes SATAN finds. It is everywhere. It has been in the news for months, with people saying that its release would bring a tsumani wave of hacker attacks, and that thousands of machines would be compromised. Some have even speculated that the Internet itself might be brought to its electronic knees.     

An engineer's guide to algorithmic structures

This tutorial paper introduces the basic concepts of the theory of algorithms, defines regular algorthmic structures and illustrates some of the advantages of using such structures for the solution of engineering problems.