An evaluation of software fault tolerance techniques in real-time safety-critical applications

The usefulness of three software fault tolerance techniques -- n-version programming, recovery blocks, and exception handling is examined within the context of real-time safety-critical environments. The general requirements of such application systems are presented and the techniques evaluated with regard to how well they satisfy these requirements

A Process Modelling Framework Based on Point Interval Temporal Logic with an Application to Modelling Patient Flows

This thesis considers an application of a temporal theory to describe and model the patient journey in the hospital accident and emergency (A&E) department. The aim is to introduce a generic but dynamic method applied to any setting, including healthcare. Constructing a consistent process model can be instrumental in streamlining healthcare issues. Current process modelling techniques used in healthcare such as flowcharts, unified modelling language activity diagram (UML AD), and business process modelling notation (BPMN) are intuitive and imprecise. They cannot fully capture the complexities of the types of activities and the full extent of temporal constraints to an extent where one could reason about the flows. Formal approaches such as Petri have also been reviewed to investigate their applicability to the healthcare domain to model processes. Additionally, to schedule patient flows, current modelling standards do not offer any formal mechanism, so healthcare relies on critical path method (CPM) and program evaluation review technique (PERT), that also have limitations, i.e. finish-start barrier. It is imperative to specify the temporal constraints between the start and/or end of a process, e.g., the beginning of a process A precedes the start (or end) of a process B. However, these approaches failed to provide us with a mechanism for handling these temporal situations. If provided, a formal representation can assist in effective knowledge representation and quality enhancement concerning a process. Also, it would help in uncovering complexities of a system and assist in modelling it in a consistent way which is not possible with the existing modelling techniques. The above issues are addressed in this thesis by proposing a framework that would provide a knowledge base to model patient flows for accurate representation based on point interval temporal logic (PITL) that treats point and interval as primitives. These objects would constitute the knowledge base for the formal description of a system. With the aid of the inference mechanism of the temporal theory presented here, exhaustive temporal constraints derived from the proposed axiomatic system’ components serves as a knowledge base. The proposed methodological framework would adopt a model-theoretic approach in which a theory is developed and considered as a model while the corresponding instance is considered as its application. Using this approach would assist in identifying core components of the system and their precise operation representing a real-life domain deemed suitable to the process modelling issues specified in this thesis. Thus, I have evaluated the modelling standards for their most-used terminologies and constructs to identify their key components. It will also assist in the generalisation of the critical terms (of process modelling standards) based on their ontology. A set of generalised terms proposed would serve as an enumeration of the theory and subsume the core modelling elements of the process modelling standards. The catalogue presents a knowledge base for the business and healthcare domains, and its components are formally defined (semantics). Furthermore, a resolution theorem-proof is used to show the structural features of the theory (model) to establish it is sound and complete. After establishing that the theory is sound and complete, the next step is to provide the instantiation of the theory. This is achieved by mapping the core components of the theory to their corresponding instances. Additionally, a formal graphical tool termed as point graph (PG) is used to visualise the cases of the proposed axiomatic system. PG facilitates in modelling, and scheduling patient flows and enables analysing existing models for possible inaccuracies and inconsistencies supported by a reasoning mechanism based on PITL. Following that, a transformation is developed to map the core modelling components of the standards into the extended PG (PG*) based on the semantics presented by the axiomatic system. A real-life case (from the King’s College hospital accident and emergency (A&E) department’s trauma patient pathway) is considered to validate the framework. It is divided into three patient flows to depict the journey of a patient with significant trauma, arriving at A&E, undergoing a procedure and subsequently discharged. Their staff relied upon the UML-AD and BPMN to model the patient flows. An evaluation of their representation is presented to show the shortfalls of the modelling standards to model patient flows. The last step is to model these patient flows using the developed approach, which is supported by enhanced reasoning and scheduling

Proof theory for exception handling

in a tasking environmen

Formalizing structured file services for the data storage and retrieval subsystem of the data management system for Spacestation Freedom

A brief example of the use of formal methods techniques in the specification of a software system is presented. The report is part of a larger effort targeted at defining a formal methods pilot project for NASA. One possible application domain that may be used to demonstrate the effective use of formal methods techniques within the NASA environment is presented. It is not intended to provide a tutorial on either formal methods techniques or the application being addressed. It should, however, provide an indication that the application being considered is suitable for a formal methods by showing how such a task may be started. The particular system being addressed is the Structured File Services (SFS), which is a part of the Data Storage and Retrieval Subsystem (DSAR), which in turn is part of the Data Management System (DMS) onboard Spacestation Freedom. This is a software system that is currently under development for NASA. An informal mathematical development is presented. Section 3 contains the same development using Penelope (23), an Ada specification and verification system. The complete text of the English version Software Requirements Specification (SRS) is reproduced in Appendix A

Semantics of Exceptions

We describe a trace semantics of exceptions and then derive a weakest precondition semantics. A program that contains exceptions terminates in one of two possible ways (if it terminates at all): either it terminates exceptionally or it terminates normally. We will therefore consider weakest preconditions that are functions of two postconditions. As a preparation we study aribitrary functions of two arguments, and their compositions

Quantum field theory as eigenvalue problem

A mathematically well-defined, manifestly covariant theory of classical and quantum field is given, based on Euclidean Poisson algebras and a generalization of the Ehrenfest equation, which implies the stationary action principle. The theory opens a constructive spectral approach to finding physical states both in relativistic quantum field theories and for flexible phenomenological few-particle approximations. In particular, we obtain a Lorentz-covariant phenomenological multiparticle quantum dynamics for electromagnetic and gravitational interaction which provides a representation of the Poincare group without negative energy states. The dynamics reduces in the nonrelativistic limit to the traditional Hamiltonian multiparticle description with standard Newton and Coulomb forces. The key that allows us to overcome the traditional problems in canonical quantization is the fact that we use the algebra of linear operators on a space of wave functions slightly bigger than traditional Fock spaces.Comment: 32 page

Process as a world transaction

Transaction is process closure: for a transaction is the limiting process of process itself. In the process world view the universe is the ultimate (intensional) transaction of all its extensional limiting processes that we call reality. ANPA’s PROGRAM UNIVERSE is a computational model which can be explored empirically in commercial database transactions where there has been a wealth of activity over the real world for the last 40 years. Process category theory demonstrates formally the fundamental distinctions between the classical model of a transaction as in PROGRAM UNIVERSE and physical reality. The paper concludes with a short technical summary for those who do not wish to read all the detail

C# PROGRAM VERIFICATION PROBLEMS:\ud SOLUTION BY A THREE-LEVEL METHOD\ud

The evolution of formal methods allowed us to overcome many obstacles in verification of procedural programs. However, wide spreading of object-oriented languages has brought new challenges, even in the case of sequential programs. These problems were thoroughly exam-ined by ESC/Java and Spec#, though in many cases they just state the presence of the challenge. This paper presents an overview of some problematic issues and a three-level approach to their solution in the C#-light project.----------------\ud Развитие формальных методов позволило решить многие вопросы верификации процедурных программ. Однако, широкое распространение объектно-ориентированных языков выявило новые проблемы даже для последовательных программ. Эти проблемы были детально исследованы в проектах ESC/Java и Spec#, но решение предлагалось в редких случаях. В этой статье рассмотрены некоторые из проблем и их решение с помощью трехуровневого подхода в проекте C#-light.\u