Maurelio Boari

Language Features for Access Control

The properties of a capability-based protection mechanism to be incorporated in a language for concurrent programming are presented. The protection mechanism is first abstractly characterized in terms of a protection model; the components of the protection mechanism, that is, the objects, subjects, and protection rules which govern the accessing to the objects by the subjects, are defined.

Middleware for automatic dynamic reconfiguration of context-driven services

In the emerging ubiquitous Internet scenario users require to access services and contents from anywhere, at anytime and with any device. Service and content provisioning platforms have to address several ubiquity challenges such as mobility, multimodality, context-awareness and content adaptation. However, current solutions fail to comprehensively face ubiquity challenges as they lack a unified approach and provide only limited sets of features. We claim that an integrated ubiquity support can stem from a simplicity principle: our middleware approach pushes the logic to face ubiquity issues outside the core layer, by keeping only management and coordination responsibilities. That succeeds in making the middleware design clearer and neater. This article presents the key architectural aspects of our platform for ubiquitous dynamic context-driven service provisioning and reconfiguration. To practically show the viability of our approach, we also provide implementation details and description of typical use cases.

Middleware for Automatic Dynamic Reconfiguration of Context-Driven Services

In the emerging ubiquitous Internet scenario users require to access services and contents from anywhere, at anytime and with any device. Due to this requirement, platforms for service and content provisioning have to address several problems related to the new issues of mobility, multimodality, context awareness and content adaptation. However, current ubiquitous service provisioning platforms still suffer a main drawback: they often underestimate platform logic complexity when multiple ubiquity features should be provided. As a result, the proposed solutions lack a unified approach to the ubiquity issues and provide only limited sets of features. We claim that an integrated and comprehensive solution can stem from a simplicity principle: our approach pushes ubiquity features outside the core middleware layer, by keeping only management and coordination responsibilities. That succeeds in making the middleware design clearer and neater. In this paper we present the key architectural aspects of our middleware platform for ubiquitous dynamic context-driven service provisioning and reconfiguration. We also provide implementation details and description of typical use cases our platform successfully realizes.

Programming environments for transputer-based architectures

Major requirements of a massively parallel programming environment are defined. The transputer peculiarities and the programming model of the transputer architecture are evaluated. The desiderata of a programming environment for a massively parallel architecture are analyzed. The models underlying a generic programming environment for massively parallel architecture are defined. The programming environments Express, Helios, and the Computing Surface CSTools are analyzed.<<ETX>>

Linguistic mechanisms for resource management strategies

In this paper a unified set of linguistic features for providing a very flexible range of resource management strategies is presented. These features may be embedded in an object oriented programming language with abstract data type definitions. Firstly some of the more frequently used resource management strategies are illustrated and the related problems of resource allocation, access and synchronization are discussed. Then linguistic mechanisms to allow static and dynamic resource allocation, static access control and synchronization are presented. Finally some examples, reflecting a wide range of resource management strategies, are discussed in order to illustrate the application of the proposed linguistic features.

A routing strategy for object-oriented applications in massively parallel architectures

Parallel object-oriented environments have a high degree of dynamicity and need specialised support to achieve efficiency of execution. Static strategies are not suitable for these environments: any prediction before execution can only roughly estimate the real behaviour. In object-oriented environments, the decision to create/destroy objects is usually taken at run-time and object allocation can change during the execution. The requirement of dynamicity should be considered in the design of every component of the support. The routing system, for instance, must ensure delivery even in case of object dynamic allocation/reallocation. The paper argues that routing algorithms for parallel object-oriented environments in massively parallel architectures should be both adaptive and efficient. We adopted a routing strategy designed to be effective in case of objects dynamically created/destroyed and capable of moving during the execution. Our adaptive strategy does not assume any knowlegde of both object allocation and system topology configuration.

Coordination for the internet of services: A user-centric approach

In the evolving ubiquitous Internet landscape, users are willing to play a more central role by modeling and reshaping the Web experience upon their needs. They begin perceiving and exploiting the Web as a platform to collaboratively create and share contents and to communicate with each other. Moreover, they want to decide how to access services and contents, freeing themselves from traditional fixed PCs and adopting heterogeneous wireless devices such as palmtops, smartphones, wireless-enabled portable audio players and so on. The Internet of services scenario stresses several research fields, from multimodality to mobility, from context awareness to service orientation and coordination. Research achievements, anyway, often tend to evolve separately, leading to ad-hoc solutions for specific sets of problems. We strongly believe that such evolving scenarios require a comprehensive support platform: this paper promotes a novel service-oriented middleware to assist users in the pervasive ubiquitous Internet access. The use cases we describe focus on complex scenarios that, in our opinion, will likely be more and more required in the next years.

Protection in languages for real time programming

A protection mechanism which may be embedded in an object oriented language for real time programming permitting definition of abstract data types, is proposed in this paper.

Multiple access to a tree in the context of readers and writers problem

In this paper we study the problem of synchronizing the access of readers and writers processes to a set of tree structured resources. More precisely we assume that the resources are hierarchically organized, xhat is the information stored in the resources of a lower level specifies the one stored in the resources of upper levels. Such kind of problem may occur, for instance, in the context of large shared data base. In fact, the yossibility that more processes accede simultaneously to the resources oi the data base, makes it necessary to introduce some lock mechanism for protecting the data base integrity [ 11. In order to allow the processes to lock the resources at various levels of granularity (i.e.: data base, area, file, record) some kind of hierarchy is usually introduced among the resources of the data base; the choice of lock granularity and the corresponding hierarchical organization of the resources is discussed in [2]. In stating a solution to this synchronization problem the existing correlation among the resources must be considered. In particular an access request for each resource, to read or write, is implicitly equivalent to a request of the same type for all the resources connected to it and belonging to the lower level of the hierarchy. A first approximation solution to the problem has been reported in [3], [4] ; a more complete solution even in the case of direct zyclic graphs of resources as been presented in [2]. The principal aim of the solution is to obtain a high utilization of resources by allowing as many processes as possible to accede simultaneously to them. In the case that a process requests access of additional resources while holding control of other ones, *the presented solution is not oeadlock free. The prop erties of the deadlock problem in the context of large shared data base are widely discussed in [ 1 ] ; in this paper the implica ,ons on deadlock problem of the .particular organization of the resources and of the access modalities of the process are discussed.

Sulla soluzione numerica di sistemi di equazioni differenziali lineari con condizioni al contorno

SommrioVengono presentati due metodi di calcolo per la soluzione numerica di sistemi di equazioni differenziali lineari con condizioni al contorno. Tali metodi, adottando opportuni sviluppi in serie di potenze consentono la determinazione delle componenti incognite del vettore-C delle condizioni iniziali con una maggiore precisione, ed una notevole riduzione del tempo di calcolo rispetto al procedimento classico che fa uso di metodi di integrazione numerica passo-passo.Tali vantaggi vengono messi in evidenza in un esempio di calcolo in cui si confrontano i risultati ottenuti con i diversi metodi di soluzione.AbstractTwo numerical methods for the solution of a linear differential system with boundary conditions are presented. These methods, through suitable developments in power series, make it possible to determine the unknown components of the vector of the initial conditions with greater accuracy and considerable reduction in calculation time compared with the classical methods using step by step numerical integration.Such calculation techniques are, furthemore, particulary useful where an analysis is required of the behaviour of the solution where the coefficient matrix or the vector of forcing function are varied.These advantages are brought out in an example in which the results obtained by the various methods are compared.