Juan Hernández Núñez

Coordinated Roles: Promoting Re-usability of Coordinated Active Objects Using Event Notification Protocols

Nowadays, the need for developing more and more complex applications with distributed capabilities has promoted the development of coordination models. The goal of these models is to express the synchronized interaction among the different components of a distributed application. Whilst the Concurrent Object Oriented Programming (COOP) paradigm has revealed special adaptation to the modeling of distributed applications, the integration of this paradigm with current coordination models results in a reduction of the potential re-usability of classes that negates the capital benefit of object orientation. The main contributions of this paper are twofold. Firstly, the Event Notification Protocols, a mechanism that permits the transparent monitoring of active objects, are presented. Secondly, Coordinated Roles, a general-purpose coordination model based on the event notification protocols is proposed. Coordinated Roles is integrated with the COOP paradigm in such a way that the reduction of re-usability is avoided. In addition, it provides flexibility, composability, polymorphism, distribution, and dynamic change of coordination patterns.

Run-Time Adaptability of Synchronization Policies in Concurrent Object Oriented Languages

Adaptability and composability have become two of the most important research areas in concurrent object-oriented systems in recent years. Nevertheless, at the present time, COOLs do not provide enough support for the development of true adaptable and composable software because either i) the different aspects that appear in these systems, synchronization and behavior, are mixed in the same component or, ii) if they are properly separated in different components, once these components are woven the resulting executable piece of software is too rigid to be adapted or reconfigured at run-time. Our contention is that this last feature is very important in critical control systems where, due to unexpected environment changes, urgent and not preestablished decisions must be taken at run-time. From security and economic point of views, it is not admissible to stop the application, adapt it to the new environment and re-run it. In this context, under project PRI97C161 of Junta de Extremadura, we have developed the Disguises Model, a model mainly thought for a clear separation of synchronization and behavioral aspects. A new language for the specification of the composition rules between the synchronization and behavioral aspects is provided, allowing synchronization policies to be added, replaced or reconfigured at run-time, which is the main contribution of the proposed model.

Guaranteeing Coherent Software Systems when Composing Coordinated Components

Latest trends in coordination models and languages suggest that it must be supported the separated specification of and the dynamic change of coordination constraints. However, little attention has been paid to guaranteeing that, the application of a separately specified coordination pattern to a set of encapsulated objects, or changing the coordination constraints of a software system at run-time, will not produce semantic errors. These kinds of errors would produce an unpredictable system and, consequently, a lack of software quality. In this paper, a method of generating formal interpretable specifications for the reproduction of coordinated environments is presented. The benefits provided by this method are: (i) easy specification, verification and detection of inconsistencies when composing coordination and functional components, (ii) easy verification and detection of inconsistencies where coordination policies are changed dynamically and (iii) simulation of coordinated behaviors. The method is based on the use of the formal specification language Maude (as a simulation tool) and a coordination model. Although the paper adopts Coordinated Roles, it is also shown how the method can be adapted to other compositional coordination models.

Multi-dimensional Declustering Methods for Parallel Database Systems

This paper describes and evaluates new methods for relation declustering in parallel databases. To process queries in parallel, relations are partitioned across multiple processors, typically by using the value of one single attribute. This kind of declustering has resulted in poor performance in the presence of data skew. Alternatively, the work contained herein proposes several strategies to decluster a relation through the use of multiple attributes. To demonstrate the validity of our approach, a thorough performance evaluation is done. The findings demonstrate the effectiveness of this kind of partitioning methods as opposed to traditional ones. In addition we analyze the performance of the different strategies relative to the speed-up and scale-up metrics.