A Flexible and Secure Deployment Framework for Distributed Applications

This paper describes an implemented system which is designed to support the deployment of applications offering distributed services, comprising a number of distributed components. This is achieved by creating high level placement and topology descriptions which drive tools that deploy applications consisting of components running on multiple hosts. The system addresses issues of heterogeneity by providing abstractions over host-specific attributes yielding a homogeneous run-time environment into which components may be deployed. The run-time environments provide secure binding mechanisms that permit deployed components to bind to stored data and services on the hosts on which they are running.Comment: 2nd International Working Conference on Component Deployment (CD 2004), Edinburgh, Scotlan

Variadic genericity through linguistic reflection : a performance evaluation

This work is partially supported by the EPSRC through Grant GR/L32699 “Compliant System Architecture” and by ESPRIT through Working Group EP22552 “PASTEL”.The use of variadic genericity within schema definitions increases the variety of databases that may be captured by a single specification. For example, a class of databases of engineering part objects, in which each database instance varies in the types of the parts and the number of part types, should lend itself to a single definition. However, precise specification of such a schema is beyond the capability of polymorphic type systems and schema definition languages. It is possible to capture such generality by introducing a level of interpretation, in which the variation in types and in the number of fields is encoded in a general data structure. Queries that interpret the encoded information can be written against this general data structure. An alternative approach to supporting such variadic genericity is to generate a precise database containing tailored data structures and queries for each different instance of the virtual schema.1 This involves source code generation and dynamic compilation, a process known as linguistic reflection. The motivation is that once generated, the specific queries may execute more efficiently than their generic counter-parts, since the generic code is “compiled away”. This paper compares the two approaches and gives performance measurements for an example using the persistent languages Napier88 and PJama.Postprin

Linguistic Reflection in Java

Reflective systems allow their own structures to be altered from within. Here we are concerned with a style of reflection, called linguistic reflection, which is the ability of a running program to generate new program fragments and to integrate these into its own execution. In particular we describe how this kind of reflection may be provided in the compiler-based, strongly typed object-oriented programming language Java. The advantages of the programming technique include attaining high levels of genericity and accommodating system evolution. These advantages are illustrated by an example taken from persistent programming which shows how linguistic reflection allows functionality (program code) to be generated on demand (Just-In-Time) from a generic specification and integrated into the evolving running program. The technique is evaluated against alternative implementation approaches with respect to efficiency, safety and ease of use.Comment: 25 pages. Source code for examples at http://www-ppg.dcs.st-and.ac.uk/Java/ReflectionExample/ Dynamic compilation package at http://www-ppg.dcs.st-and.ac.uk/Java/DynamicCompilation

Définition, mise en forme et évaluation du concept de boîte à outils pour des activités interactives d'apprentissage

Utilisation des tic dans l'enseignement -- Étude empirique et évaluation d'outils disponibles -- Analyse des requis et description du concept -- Conception et développement du prototype expérimental -- Tests utilisateurs

A Boxer architecture and interface

The Boxer computational environment shows great promise not just as a teaching tool, but as a ubiquitous computational medium. To date, research into Boxer has concentrated mainly on the social impact of such a media, while less effort has been expended on the implementation or interface aspects of the project. This thesis outlines a possible architecture for a new implementation of Boxer, taking advantage of some fields of computer science that have matured over the last decade. Also, a new user interface for Boxer has been developed with the intention of providing easier access to Boxer for new and infrequent users. This interface is described and evaluated

Delivering the benefits of persistence to system construction and execution

In an orthogonally persistent programming system the longevity of data is independent of its other attributes. The advantages of persistence may be seen primarily in the areas of data modelling and protection resulting from simpler semantics and reduced complexity. These have been verified by the first implementations of persistent languages, typically consisting of a persistent store, a run-time system and a compiler that produces programs that may access and manipulate the persistent environment. This thesis demonstrates that persistence can deliver many further benefits to the programming process when applied to software construction and execution. To support the thesis, a persistent environment has been extended with all the components necessary to support program construction and execution entirely within the persistent environment. This is the first known example of a strongly-typed integrated persistent programming environment. The keystone of this work is the construction of a compiler that operates entirely within the persistent environment. During its construction, persistence has been exploited in the development of a new methodology for the construction of applications from components and in the optimisation of the widespread use of type information throughout the environment. Further enhancements to software construction and execution have been developed that can only be supported within an integrated persistent programming environment. It is shown how persistence forms the basis of a new methodology for dynamic optimisation of code and data. In addition, new interfaces to the compiler are described that offer increased functionality over traditional compilers. Extended by the ability to manipulate structured values within the persistent environment, the interfaces increase the simplicity, flexibility and efficiency of software construction and execution. Reflective and hyper-programming techniques are also supported. The methodologies and compilation facilities evolved together as the compiler was developed and so the first uses of both were applied to one another. It is these applications that have been described in this thesis as examples of its validity. However, the methodologies and the compilation facilities need not be inter-twined. The benefits derived from each of them are general and they may be used in many areas of the persistent environment

Reflection and hyper-programming in persistent programming systems

In an orthogonally persistent programming system, data is treated in a manner independent of its persistence. This gives simpler semantics, allows the programmer to ignore details of long-term data storage and enables type checking protection mechanisms to operate over the entire lifetime of the data. The ultimate goal of persistent programming language research is to reduce the costs of producing software. The work presented in this thesis seeks to improve programmer productivity in the following ways: • by reducing the amount of code that has to be written to construct an application; • by increasing the reliability of the code written; and • by improving the programmer’s understanding of the persistent environment in which applications are constructed. Two programming techniques that may be used to pursue these goals in a persistent environment are type-safe linguistic reflection and hyper-programming. The first provides a mechanism by which the programmer can write generators that, when executed, produce new program representations. This allows the specification of programs that are highly generic yet depend in non-trivial ways on the types of the data on which they operate. Genericity promotes software reuse which in turn reduces the amount of new code that has to be written. Hyper-programming allows a source program to contain links to data items in the persistent store. This improves program reliability by allowing certain program checking to be performed earlier than is otherwise possible. It also reduces the amount of code written by permitting direct links to data in the place of textual descriptions. Both techniques contribute to the understanding of the persistent environment through supporting the implementation of store browsing tools and allowing source representations to be associated with all executable programs in the persistent store. This thesis describes in detail the structure of type-safe linguistic reflection and hyper-programming, their benefits in the persistent context, and a suite of programming tools that support reflective programming and hyper-programming. These tools may be used in conjunction to allow reflection over hyper-program representations. The implementation of the tools is described