Terminal area flight path generation using parallel constraint propagation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1989.Includes bibliographical references (leaves 179-185).by Michel Marc Sadoune.Ph.D

Terminal area flight path generation using parallel constraint propagation

Cover titleMay 1989Also issued as an Ph.D. thesis, Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1989Includes bibliographical references (p. 175-181)A Flight Path Generator is defined as the module of an automated Air Traffic Control system which plans aircraft trajectories in the terminal area with respect to operational constraints. The flight path plans have to be feasible and must not violate separation criteria. The problem of terminal area trajectory planning is structured by putting the emphasis on knowledge representation and air-space organization. A welldefined and expressive semantics relying on the use of flexible patterns is designed to represent aircraft motion and flight paths. These patterns are defined so as to minimize the need for replanning and to smoothly accommodate operational deviations. Flight paths are specified by an accumulation of constraints. A parallel, asynchronous implementation of a computational model based on the propagation of constraints provides mechanisms to efficiently build feasible flight path plans. A methodology for a fast and robust conflict detection between flight path plans is introduced. It is based on a cascaded filtering of the stream of feasible flight paths and combines the benefits of a symbolic representation and of numerical computation with a high degree of parallelism. The Flight Path Generator is designed with the goal of implementing a portable and evolving tool which could be inserted in controllers' routine with minimum disruption of present procedures. Eventually, a model of aircraft interaction provides a framework to rethink the notion of Separation Standards

Vertical foreclosure: a policy framework

Whenever you phone your mother, switch on the light, or buy health insurance you purchase a service or product from a chain of vertically related industries. Providers of these products or services need access to a telecommunications network, an electricity network or to health care services. In such industries, integration and exclusive contracts between vertically related firms may have important welfare enhancing effects, but can also deny or limit rivals' access to input or customers, leading to foreclosure. Foreclosure can harm welfare if it reduces competition. This document provides policymakers with a framework to assess the potential for welfare reducing foreclosure of vertical integration and vertical restraints and describes possible remedies. The framework consists of four steps. Each step requires its own detailed analysis. First, market power should exist either upstream or downstream. Second, a theory of foreclosure should be formulated that explains why foreclosure is a profitable equilibrium strategy. Third, the existence and magnitude of potential welfare enhancing effects of the vertical restrains or vertical integration should be assessed. Fourth, suitable policies to address foreclosure should be found.

Knowledge Components and Methods for Policy Propagation in Data Flows

Data-oriented systems and applications are at the centre of current developments of the World Wide Web (WWW). On the Web of Data (WoD), information sources can be accessed and processed for many purposes. Users need to be aware of any licences or terms of use, which are associated with the data sources they want to use. Conversely, publishers need support in assigning the appropriate policies alongside the data they distribute. In this work, we tackle the problem of policy propagation in data flows - an expression that refers to the way data is consumed, manipulated and produced within processes. We pose the question of what kind of components are required, and how they can be acquired, managed, and deployed, to support users on deciding what policies propagate to the output of a data-intensive system from the ones associated with its input. We observe three scenarios: applications of the Semantic Web, workflow reuse in Open Science, and the exploitation of urban data in City Data Hubs. Starting from the analysis of Semantic Web applications, we propose a data-centric approach to semantically describe processes as data flows: the Datanode ontology, which comprises a hierarchy of the possible relations between data objects. By means of Policy Propagation Rules, it is possible to link data flow steps and policies derivable from semantic descriptions of data licences. We show how these components can be designed, how they can be effectively managed, and how to reason efficiently with them. In a second phase, the developed components are verified using a Smart City Data Hub as a case study, where we developed an end-to-end solution for policy propagation. Finally, we evaluate our approach and report on a user study aimed at assessing both the quality and the value of the proposed solution

On the engineering of crucial software

The various aspects of the conventional software development cycle are examined. This cycle was the basis of the augmented approach contained in the original grant proposal. This cycle was found inadequate for crucial software development, and the justification for this opinion is presented. Several possible enhancements to the conventional software cycle are discussed. Software fault tolerance, a possible enhancement of major importance, is discussed separately. Formal verification using mathematical proof is considered. Automatic programming is a radical alternative to the conventional cycle and is discussed. Recommendations for a comprehensive approach are presented, and various experiments which could be conducted in AIRLAB are described