1,721,360 research outputs found
Concurrency within objects: layered approach
No full textObject-oriented systems have provided a new methodology for decomposing problems. They have also brought out the issue of the specification of concurrency in a more structured manner. The paper shows how the Parallel Objects (PO) model addresses the problem of supporting concurrency. PO is a parallel object-oriented model. Any entity/object is capable of independent execution and in addition several concurrent activities can exist within the same object. In fact, as a feature distinguished from other concurrent object systems, PO does not strive to obtain intra-object sequentialization. In PO, the specification of concurrency can take advantage of a layered approach. Depending on user skill, the system requires more or less deep insight of PO to specify concurrency. A novice user can derive the specification of object concurrency from the PO environment. This approach stresses the reuse principle typical of object systems, i.e., inheritance. The PO environment makes it possible for skilled users to investigate complex concurrency policies and their performances for the same application. © 1991
Static vs. Dynamic Issues in OO Programming Languages
No full textAny decision in the design of both object-oriented programming languages (OOPLs) and their environments must face the choice between static and dynamic issues. The aim of this article is to discuss the implications of the static vs. dynamic choices. Despite the fact that dynamic choices induce runtime costs, the resulting flexibility permits the rapid prototyping of applications and reduces application development time. On the other hand, static strategies may even increase development time in applying early controls to all phases of development steps, but can greatly shorten maintenance and lifetime consistency phases.This article tries to establish a trafe-off between static and dynamic perspectives both to help programmers choose the most convenient OO language/environment for their applications and to help designers introduce static/dynamic property melding into their project developments. Well-know OOPLs are used to exemplify static and dynamic properties – the chosen languages are Smalltalk-80, Eifell, C++ and Java. Their selection stems from thei relevance within the OO community
PROM: A support for robust replication in a distributed object environment
No full textThe concept of object can be employed to achieve tolerance to hardware faults in distributed systems. Replication by introducing several copies for each object allows a continuous service even in case of failure. In particular, the paper describes an object model, PROM, which exploits replication by defining several passive back-up copies for any object. The system automatically recovers any failure of a copy in execution by activating a spare copy and restarting it from a previous checkpoint. The aim of the paper is the analysis of the effective support for PROM. This support is organized in structured levels on a distributed architecture. The services that the support should include to guarantee the desired replication model are described. © 1990, Science Press, Beijing China and Allerton Press Inc.. All rights reserved
The role of opaque types to build abstractions
No full textThis note examines the MODULA-2 approach to build data abstractions and abstract data types. MODULA-2 provides a byreference semantics by providing opaque types via pointers. The paper compares this mechanism with the one furnished by ADA (*). A comparison with object-oriented systems brings out the issue of assignment, copy and compare operations. That leads to a constructive methodology for abstract data types in MODULA-2. Any abstraction must furnish copy operations with two different semantics, respectively shallow and deep, and related equality and inequality operations. © 1988, ACM. All rights reserved
HOLMES: a Tool for Monitoring Heterogeneous Architectures
No full textMonitoring tools are necessary components in the support of distributed applications and can be used to provide dependability, debugging and testing, to enhance the performance and to make possible the run-time steering of applications. These tools are needed to exploit in the best way all the available high performance computing resources of a heterogeneous environment. This paper describes HOLMES, an on-line monitoring system designed to support dynamic management of resources that requires run-time measurement. HOLMES identifies the evolving system state and provides the necessary information to any dynamic policy to assign resources by following application evolution. HOLMES makes possible to control and steer an application even distributed across heterogeneous architectures, from parallel machines to clusters of workstations and PCs
How to support Internet-based distribution of video on demand to portable devices
No full textThe increasing diffusion of mobile computing and of portable devices with wireless connectivity identifies new challenging scenarios for service provisioning. The access from devices with limited heterogeneous capabilities to traditional and novel Internet services requires new infrastructures capable of integrating with the fixed network and of supporting service tailoring/adaptation. The paper presents a mobile agent-based middleware for the distribution of video on demand (VoD) to portable devices. Mobile agents can act as device proxies over the fixed network, can negotiate the proper QoS level and can dynamically tailor VoD flows depending on profiles of terminal characteristics and user preferences. The paper also describes the design and implementation of a motion picture-information service prototype, built on top of the proposed middleware. The prototype shows the feasibility of distributing motion picture trailers ubiquitously even to portable devices with strict constraints on computing power and visualization capabilities, e.g., Palm personal digital assistants hosting the Java KVM/CLDC/MIDP software suite. © 2002 IEEE
Mobile middleware solutions for the adaptive management of multimedia QoS to wireless portable devices
No full textNew challenging service scenarios are integrating wireless portable devices with limited and heterogeneous capabilities. They are expected to access both traditional and novel (context-dependent) Internet services. This not only calls for novel infrastructures to support the integration of mobile devices with the fixed network, but also stresses the necessity of negotiation-time tailoring and provision-time adaptation of Quality of Service (QoS). The paper presents a flexible and dynamic middleware for the management of multimedia QoS to wireless devices that can roam during service provisioning. The middleware exploits mobile agents that act as device shadow proxies over the fixed network to transparently follow the device movements between wireless localities, to negotiate the proper QoS level, and to dynamically adapt multimedia flows depending on device profiles and user preferences. In particular, the paper focuses on how the middleware achieves the on-line visibility of the device change of locality in a portable way over different implementations of different wireless technologies, i.e., IEEE 802.11 and Bluetooth. The first experimental results show that, notwithstanding the application-level approach, the middleware reorganization time is compatible with the requirements imposed by the addressed multimedia scenario
La danza : polka mazurka / composée pour le piano par A. Corradi,...
No full textTitre uniforme : Corradi, A. (18..-18.. ; compositeur). Compositeur. [La danza. Piano]Polkas-mazurkas (piano) -- +* 1800......- 1899......+:19e siècle:Piano, Musique de -- +* 1800......- 1899......+:19e siècle
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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