Alan Dearle

A framework for constraint-based development and autonomic management of distributed applications

We propose a framework for the deployment and subsequent autonomic management of component-based distributed applications. An initial deployment goal is specified using a declarative constraint language, expressing constraints over aspects such as component-host mappings and component interconnection topology. A constraint solver is used to find a configuration that satisfies the goal, and the configuration is deployed automatically. The deployed application is instrumented to allow subsequent autonomic management. If, during execution, the manager detects that the original goal is no longer being met, the satisfy/deploy process can be repeated automatically in order to generate a revised deployment that does meet the goal.

Persistent Hyper-Programs

The traditional representation of a program as a linear sequence of text forces a particular style of program construction to ensure good programming practice. Tools such as syntax directed editors, compilers, linkers and file managers are required to translate and execute these linear sequences of text. At some stage in the execution sequence the source text is checked for type correctness and its translated form linked to values in the environment. When this is performed early in the execution process confidence in the correctness of the program is raised, at the cost of some flexibility of use.

Safe browsing in a strongly typed persistent environment

The need to examine data structures often occurs in programming language and database management systems. In this paper we describe how a browser for a strongly typed programming language ( PS-algol ) may be written in a type secure manner in a closed persistent environment. This is achieved without resorting to magic or having to break the type rules of the language by exploiting a compiler that is a object with full civil rights in the environment. The use of impact of such an object is discussed. Safe Browsing in a Strongly Typed Persistent Environment Page 3

An ad hoc approach to the implementation of polymorphism

Polymorphic abstraction provides the ability to write programs that are independent of the form of the data over which they operate. It has proved difficult to provide efficient implementations of polymorphism. This paper addresses this problem and describes a new technique which can implement all forms of polymorphism, use a conventional machine architecture and support non-uniform data representations. Furthermore, the method ensures that any extra cost of implementation applies to polymorphic forms only and allows such polymorphic forms to persist over program invocations.

Operating system support for persistent and recoverable computations

The principal tasks of an operating system are to manage the resources of the system, maintain the permanent data of the system and to provide an efficient environment for the execution of user programs. In conventional operating systems these tasks are centred around the file system as the repository of permanent data and virtual memory as the execution environment. Persistent systems offer an alternative view in which the lifetime of data is separated from the access mechanism. In a persistent system all data, regardless of its lifetime, is created and manipulated in a uniform manner. When persistence is included as the basic abstraction of an operating system, many of the inadequacies of existing operating systems are eliminated and the tasks of an application developer are greatly simplified. This results in major improvements both in terms of program development time and execution efficiency. Grasshopper, a persistent operating system being developed by the authors, provides a testbed for the demonstration of these claims.

Architectural Support for Global Smart Spaces

A GLObal Smart Space (GLOSS) provides support for interaction amongst people, artefacts and places while taking account of both context and movement on a global scale. Crucial to the definition of a GLOSS is the provision of a set of location-aware services that detect, convey, store and exploit location information. We use one of these services, hearsay, to illustrate the implementation dimensions of a GLOSS. The focus of the paper is on both local and global software architecture to support the implementation of such services. The local architecture is based on XML pipelines and is used to construct location-aware components. The global architecture is based on a hybrid peer-to-peer routing scheme and provides the local architectures with the means to communicate in the global context.

The Persistent Abstract Machine

The Persistent Abstract Machine is an integral part of a layered architecture model to support the Napier language. It interfaces cleanly with a persistent store, and allows persistence to be implemented without difficulty in a high-level language. The heap based storage mechanism of the Persistent Abstract Machine is designed to support the block retention nature of the Napier language. This allows the implementation of first ciass procedures and modules in programming languages with the minimum of effort. A primitive type system within the machine contains just enough information to allow machine instructions which behave differently according to the dynamic type of their operands. This type system, in conjunction with the block retention architecture, may be used to great effect to provide a fast implementation of polymorphic procedures, abstract data types, inheritance and bounded universal quantification.

Toward ubiquitous environments for mobile users

A computational paradigm that lets processes migrate with users would support truly ubiquitous computing environments. The article investigates the technical problems that must be solved to accommodate this model and examines some systems that are addressing the problems now. The review of current systems addressing these issues reveals that it is now possible to engineer a system in which the users entire environment is available wherever and whenever it is required. However, the provision of such an environment represents a considerable engineering effort and many significant choices. At the University of Stirling, we are currently investigating these choices in the construction of a ubiquitous environment based on Java.

The Napier Type System

Persistent programming is concerned with the construction of large and long lived systems of data. In designing and building persistent object systems, we are attempting to regularise the activities that are performed on data by programming languages, operating systems, database management systems and file systems. We have identified the following areas of research which we are investigating in the context of persistent systems. They are: controlling complexity, protection of data, orthogonal persistence, controlled system evolution and concurrent computation.

An examination of operating system support for persistent object systems

Examines operating system support for persistent systems that execute on conventional hardware architectures. The focus of the paper is to examine the inadequacies of traditional operating systems as vehicles for the construction of persistent systems. The authors concentrate on four major areas, namely addressing, stability and resilience, process management and protection. They examine the consequences of making the operating system kernel itself persistent. They conclude by outlining the requirements which must be met by future operating systems designed to support orthogonal persistence.<<ETX>>