The Problem of Mutual Exclusion: A New Distributed Solution

In both centralized and distributed systems, processes cooperate and compete with each other to access the system resources. Some of these resources must be used exclusively. It is then required that only one process access the shared resource at a given time. This is referred to as the problem of mutual exclusion. Several synchronization mechanisms have been proposed to solve this problem. In this thesis, an effort has been made to compile most of the existing mutual exclusion solutions for both shared memory and message-passing based systems. A new distributed algorithm, which uses a dynamic information structure, is presented to solve the problem of mutual exclusion. It is proved to be free from both deadlock and starvation. This solution is shown to be economical in terms of the number of message exchanges required per critical section execution. Procedures for recovery from both site and link failures are also given

Total algorithms

We define the notion of total algorithms for networks of processes. A total algorithm enforces that a "decision" is taken by a subset of the processes, and that participation of all processes is required to reach this decision. Total algorithms are an important building block in the design of distributed algorithms. For some important network control problems it can be shown that an algorithm solving it is necessarily total, and that any total algorithm can solve the problem. We study some total algorithms for a variety of network topologies. Constructions are shown to derive algorithms for Mutual Exclusion, Election, and Distributed Infirnum Approximation from arbitrary total algorithms. The paper puts many results and paradigms about designing distributed algorithms in a general framework. This report oulines several other works of the author. Total algorithms, their properties, and some additional examples, as well as traversal algorithms and the time complexity of distributed algorithms are studied in [Tel94, Chap.6]. The construction of algorithms for distributed infirnum approximation is treated in [CBT94, Tel86] and [Tel91, Sec. 4.1]

Automatic techniques for detecting and exploiting symmetry in model checking

The application of model checking is limited due to the state-space explosion problem – as the number of components represented by a model increase, the worst case size of the associated state-space grows exponentially. Current techniques can handle limited kinds of symmetry, e.g. full symmetry between identical components in a concurrent system. They avoid the problem of automatic symmetry detection by requiring the user to specify the presence of symmetry in a model (explicitly, or by annotating the associated specification using additional language keywords), or by restricting the input language of a model checker so that only symmetric systems can be specified. Additionally, computing unique representatives for each symmetric equivalence class is easy for these limited kinds of symmetry. We present a theoretical framework for symmetry reduction which can be applied to explicit state model checking. The framework includes techniques for automatic symmetry detection using computational group theory, which can be applied with no additional user input. These techniques detect structural symmetries induced by the topology of a concurrent system, so our framework includes exact and approximate techniques to efficiently exploit arbitrary symmetry groups which may arise in this way. These techniques are also based on computational group theoretic methods. We prove that our framework is logically sound, and demonstrate its general applicability to explicit state model checking. By providing a new symmetry reduction package for the SPIN model checker, we show that our framework can be feasibly implemented as part of a system which is widely used in both industry and academia. Through a study of SPIN users, we assess the usability of our automatic symmetry detection techniques in practice

Advancing the knowledge of local health care policy through the growth machine thesis.

A disciplined-configurative case study design was carried out to explore whether a growth machine exists and shapes local healthcare policy in Louisville. A historical analysis first explored whether a growth machine existed in Louisville in the past and shaped healthcare policy. Second, a network analysis was used to identify the recent contours of the Louisville growth machine. Third, qualitative interviews were conducted with central individuals as indicated by the social network analysis to assess the degree to which local healthcare policy is shaped and driven by the growth machine. The results show that Louisville has consistently had a growth machine which has shaped the limited local healthcare politics and policy allowed by the higher levels of government. The Federal Government\u27s policy to require pluralistic boards of average consumers on public health agencies actually has detached the growth machine as the local power structure from those agencies. The growth machine has not always had consensus due to differing growth agendas as demonstrated by the construction of Southwest Hospital, the break up of the University of Louisville Hospital management consortium, and the reorganization of the Louisville Medical Center Development Corporation. Regardless the growth machine has generally been able to keep the general public out of such decisions and in vi turn find new ways to be unified in the name of growth. Local government in Louisville was and continues to be a supportive player versus dominant player in the growth machine in local healthcare politics and has not been the driver of local healthcare policy

An exploration and validation of computer modeling of evolution, natural selection, and evolutionary biology with cellular automata for secondary students.

The Evolutionary Tool Kit, a new software package, is the prototype of a concept simulator providing an environment for students to create microworlds of populations of artificial organisms. Its function is to model processes, concepts and arguments in natural selection and evolutionary biology, using either Mendelian asexual or sexual reproduction, or counterfactual systems such as \u27paint pot\u27 or blending inheritance. In this environment students can explore a conceptual What if? in evolutionary biology, test misconceptions and deepen understanding of inheritance and changes in populations. Populations can be defined either with typological, or with populational thinking, to inquire into the role and necessity of variation in natural selection. The approach is generative not tutorial. The interface is highly graphic with twenty traits set as icons that are moved onto the \u27phenotypes\u27. Activities include investigations of evolutionary theory of aging, reproductive advantage, sexual selection and mimicry. Design of the activities incorporates Howard Gardner\u27s Theory of Multiple Intelligences. Draft of a teacher and student manual are included

Legal knowledge-based systems: new directions in system design

This thesis examines and critiques the concept of 'legal knowledge-based’ systems. Work on legal knowledge-based systems is dominated by work in 'artificial intelligence and law’. It seeks to automate the application of law and to automate the solution of legal problems. Automation however, has proved elusive. In contrast to such automation, this thesis proposes the creation of legal knowledge-based systems based on the concept of augmentation of legal work. Focusing on systems that augment legal work opens new possibilities for system creation and use. To inform how systems might augment legal work, this thesis examines philosophy, psychology and legal theory for information they provide on how processes of legal reasoning operate. It is argued that, in contrast to conceptions of law adopted in artificial intelligence and law, 'sensemaking' provides a useful perspective with which to create systems. It is argued that visualisation, and particularly diagrams, are an important and under considered element of reasoning and that producing systems that support diagramming of processes of legal reasoning would provide useful support for legal work. This thesis reviews techniques for diagramming aspects of sensemaking. In particular this thesis examines standard methods for diagramming arguments and methods for diagramming reasoning. These techniques are applied in the diagramming of legal judgments. A review is conducted of systems that have been constructed to support the construction of diagrams of argument and reasoning. Drawing upon these examinations, this thesis highlights the necessity of appropriate representations for supporting reasoning. The literature examining diagramming for reasoning support provides little discussion of appropriate representations. This thesis examines theories of representation for insight they can provide into the design of appropriate representations. It is concluded that while the theories of representation that are examined do not determine what amounts to a good representation, guidelines for the design and choice of representations can be distilled. These guidelines cannot map the class of legal knowledge-based systems that augment legal sensemaking, they can however, be used to explore this class and to inform construction of systems