Alcides Calsavara

Distributed Usage Control Architecture for Business Coalitions

The dynamic environment of Business Coalition (BC) requires a flexible access control approach to deal with user management and policy writing. However, the traditional approach applied to BC assigns to access control a burden, mainly to the service provider, thus requiring ad hoc schemes to mitigate the lack of controls developed to BC needs. We present a brokered access control architecture, based on UCONABC, to obtain an integrated usage control management for BC. The broker intermediates contract establishment between service provider and consumer, and derives from it the policies to regulate the usage at service-level. The consumer defines user-level policies to control the usage of the contracted services. We developed a web services based prototype to evaluate the feasibility of our proposal. The proposed architecture enables distribution of duties and integration of usage control management in a loosely coupled fashion, providing the flexibility desired in BC environments.

Autonomic Application-Level Message Delivery Using Virtual Magnetic Fields

Mobility has emerged as an important new trend in the arena of distributed computing bringing along deep social and technical transformations. These changes have created an increasing demand for applications and middleware that exploit and support mobility. This article proposes the use of the concept of magnetic fields borrowed from physics to enable self-organizing message forwarding on overlay networks over physical networks with possibly mobile nodes. Though autonomic, a network that employs the proposed message forwarding mechanism still needs a cognitive management to accomplish end-to-end goals. After formalizing the generic model of virtual magnetic fields, a distributed self-stabilizing propagation algorithm is defined and applied to the load-balancing problem. Simulation results are then discussed and implementation issues are detailed considering extensions of existing platforms. At last, conclusions are drawn and the main future works are listed.

Semantic Search Engines

Typical electronic business applications need to make queries about products and services made available by sellers and service providers through the Web. Unfortunately, it can be a very time consuming task to discover information as simple as those, since every site has its own metaphore. The so-called search engines can facilitate such task because a client provides some keywords and obtain a list of Uniform Resource Locators (URL) that point to the target sites, but it does not prevent from interacting with each site. We propose and define a novel kind of service for the Web: the semantic search engine. Differently from traditional search engines, a semantic search engine stores semantic information about Web resources and is able to solve complex queries, considering as well the context where the Web resource is targeted. We show, through examples, how a semantic search engine may be employed in order to permit clients obtain information about commercial products and services, as well as about sellers and service providers which can be hierarchically organized. Semantic search engines may seriously contribute to the development of electronic business applications since it is based on strong theory and widely accepted standards.

A framework for CORBA interoperability in ad hoc networks

The increasing popularity of wireless-enabled PDAs, laptops and smart mobile phones, in addition to an explosion in the number of mobile services and networks, makes necessary the use of supporting frameworks to assist the development of distributed applications in ad hoc networks. Starting from OMGs standards on wireless access in mobile environments, this paper focuses on additional architectural requirements for adapting and extending CORBAs interoperability model so that it can be used to transparently handle GIOP message exchanges among objects across ad hoc networks. The proposed architecture, based on federations of specialized name servers, is described along with a strategy for routing the messages. Finally, implementation details and strategies along with performance and scalability issues are discussed.

Message routing in vehicular delay-tolerant networks based on human behavior

Delay/Disruption-Tolerant Networks (DTNs) have been used in many different scenarios and are characterized by the high mobility of nodes, the constant disconnection, the high delays for message delivery and the frequent partitioning. The union of Vehicular Ad hoc Networks (VANETs) and DTNs has created a new research field in Vehicular Delay-Tolerant Networks (VDTNs) based on DTNs stored-carry-and-forward mechanism and applying it to the vehicular context. This mechanism allows messages to be routed to their destinations without the need of end-to-end connections. Due to the widespread availability of low cost on-board communication devices, message routing in VDTN has become an important research target. That is why many protocols can be found in the literature with the goal of overcoming the challenges encountered by applications developed for this context. Nevertheless, these proposed protocols do not take into consideration important requirements such as: no dependency on Road Side Units (RSU) and mechanisms to obtain information about the location of vehicles. This paper proposes and describes a message routing algorithm based on consciousness and human behavior in order to address the main demands of the VDTN environment.

A Strategy for Data Replication in Mobile Ad Hoc Networks

This paper addresses the problem of data replication in MANETs (Mobile Ad hoc Network) presenting a new solution that improves the performance of data access in such networks. To make the data available to the user at any place and any time, several issues related to the dynamics of MANETs need to be considered, particularly the nodes mobility and limited computing resources. The development of methods for data replication in this context represents, therefore, a major challenge, because a series of application-dependent requirements must be handled in a transparent and adaptive manner. One way to tackle this is through an application-level message forwarding mechanism using Virtual Magnetic Fields. In systems where fault tolerance is implemented through data replication, we show that the use of virtual magnetic fields provides an adequate paradigm in the context of dynamic factors that would influence the decision of which network nodes will keep replicas of data.

Integrating the Unreliable Multicast Inter-ORB Protocol in MJaco

This paper presents our experience in implementing OMG Unreliable Multicast Inter-ORB Protocol specifications into an ORB. An integration model is proposed to allow the coexistence of two different protocol stacks (IIOP/TCP/IP and MIOP/UDP/IP multicast) making possible a large spectrum of middleware support for distributed objects communication. That integration model is discussed in this paper, giving evidence of the compatibility of our approach with the CORBA specifications. In order to evaluate that integration, different tests were made considering interoperability, performance and scalability aspects.

The least semantically related cache replacement algorithm

This article presents the Web cache replacement algorithm named Least Semantically Related (LSR), as an alternative to well-known and widely employed replacement policies, such as SIZE, LFU and LRU, which are based on physical properties of objects (documents). LSR is based on the semantics of the information contained within objects: LSR tends to evict objects which are less related to the last object to enter the cache with respect to their semantics, therefore preserving objects of more interest to clients. A detailed algorithm and a data structure for LSR where objects are classified according to a previously established taxonomy were designed and implemented for the purposes of validation and comparison with other replacement policies. Besides, a framework for simulation was designed and verified, including the data preparation process. The initial experimental results show that LSR out-performs traditional policies in terms of hit rate, in most cases.

Routing Based on Message Attraction

Application-level message routing mechanisms are crucial to the development of distributed applications and infrastructures that are flexible, adaptable, context-aware and mobile. This paper proposes to use the concept of magnetic fields borrowed from physics in order to enable a self-organizing message routing mechanism. First, a generic model of virtual magnetic fields is presented, then a distributed self-stabilizing update protocol is defined and applied to the load-balancing problem in order to illustrate the employment of the theoretical concepts. Simulation results are then discussed.

A Paradigm Shift in the Design of Mobile Applications

Mobility has emerged as an important new trend in the arena of distributed computing bringing along with it deep social and technical transformations. These changes clearly create an increasing demand for applications and middleware that exploit and support mobility. This paper surveys the main classes of paradigms and middlewares for distributed (mobile) systems and proposes a new paradigm inspired in the concept of magnetic fields from physics. The model is then formally defined and implementation issues concerning extensions to be applied to current middlewares in order to support the paradigm are detailed. Finally, conclusions are drawn and the main future works are listed.