Catálogo de publicaciones - libros

Steganography is defined as the art and science of hiding information, it takes one piece of information and hides it within another. The piece more used to hide information are the digital images. In this paper we present a way to use unused fields in the IP header of TCP/IP packets in order to send information between to nodes over Internet.

UML Interaction diagrams (Sequence diagrams (SD), Collaboration diagrams or Communication diagrams) lack a formal semantics; they include some amount of ambiguity so that formal techniques cannot be applied e.g. for automatically deriving the behavior of the objects (as Statecharts or State-Transition diagrams) from the SD where they appear. To overcome this situation, this paper first analyses and simplifies the semantic relationships among the concepts that intervene in the definition of SDs: s ynchronous / asynchronous, activator and return messages. Then it proposes an interpretation of the precedence association among messages that yields to an operational semantics of SDs that orders the actions of emitting and receiving messages according to a causality relationship.

Nowadays on-line reconfiguration for computer networks is pursued as an alternative approach to keep performance levels when a mal function is presented in the system. In this case, reconfiguration is proposed in three stages. Firstly, computer network presents a degradation in time communication due to the appearance of certain local faults. Secondly, based upon this scenario a strategy for on-line reconfiguration is pursued in order to cover faults where new time delays appear between elements. These delays modify the behaviour of the dynamical response of the system. During third stage, the control law needs to be modified in terms of current time delays. Therefore, in this paper, on-line system reconfiguration as multivariable and multi-stage problem is pursued based upon a quasi-dynamic scheduler that takes into account those predetermined time delays and the related control law. Control law reconfiguration is pursued as soon as structural computer network reconfiguration is taken place by using current system performance.

Some new protocols handle time constraints to model important aspects (delays, timeouts, ..). This issue has to be taken into account in every step during its development life cycle, in particular in the testing step. This paper presents an integrated tool which permits to specify a timed system in various models (RT-LOTOS, IF, Timed automata) and then generates test sequences using a new efficient algorithm. Illustrated examples show the differents steps of this new test generation method.

In this paper, we suggest a methodology for testing Real Time Component Based Systems (RTCBS). A RTCBS is described as a collection of components where each component is modeled as a Timed Input-Output Automaton (TIOA). The first part of this study is devoted to the generation of timed-test sequences. Our algorithm for test sequence derivation extracts executable timed test sequences from a synchronous product between a timed test purpose (a property required on the system) and the corresponding component(s) specification. The second part presents an adequate test architecture consisting of the System Under Test (SUT) components, and a distributed tester that consists of a set of coordinating testers. Each tester is dedicated to test a single SUT component. A test execution algorithm is presented. Testing the SUT is divided into two phases. In the first phase, each of the testers tests its corresponding component in isolation. In the second phase, each tester executes only its corresponding communication timed test sequences to test the interaction between components integrated in a RTCBS, taking into consideration the synchronization of events between testers themselves.

The dynamic nature of cooperative information systems (CIS) makes considerably more difficult the task of modeling interactions among agents. One of the most difficult problems related to the dynamic of a system is how to model and control simultaneously multiple interactions among agents in a friendly way. So far, traditional approaches deal with the problem of modeling interactions in static conditions and commonly with only two agents participating concurrently in cooperative tasks. Consequently, expressiveness becomes a problem related with the representation of multiple interactions in a satisfactory way, particularly in dynamic environments, such as e-business. The paper illustrates the application of a methodology based on Coloured Petri Nets (CP nets) in order to model the interaction mechanism in a CIS in an expressive way. This reduces the associated complexity in the representation of the dynamic of the system in a contact center environment, which is the start point to customer service, where concurrent interactions among users, technical people, process center and the contact center constitute a dynamic process that needs to be permanently monitored and controlled. The methodology provides us important advantages in the representation and reasoning for the interaction mechanism modeled in CIS. The use of CP nets allows analyzing the behavior of the system in the dynamic model using the individual and structural model.

Uncertainty management and information integration have been challenging issues in AI and database research. The literature is vast and rich on either of these two issues, however, they have not been studied simultaneously in the same setting. In this work, we make a first attempt and propose a framework for information integration with uncertainty, which uses the information source tracking(IST) model [9] as the underlying certainty model. The IST model is an extension of the relational data model in which every tuple t is annotated with (a set of) fixed length vectors, called agent vectors , representing the (human or sensor) agents which confirmed t or contributed to it. Our framework consists of a dynamic collection of autonomous but cooperating IST databases, called the information sources or sites , in which each relation r is annotated with a site vector , indicating which sites contributed to the definition of r . We extend the relational algebra from the basic IST model accordingly to manipulate agent and site vectors. We also extend the reliability calculation algorithm from the basic model to compute the certainty of each answer tuple as a function of the reliabilities of the contributing agents and sites. We have developed a running prototype of the proposed framework for which we mainly used SQL programming for query rewriting and manipulation of agent and site vectors.

Workflow is the key technology for business process automation, while distributed workflow is the solution to deal with the decentralized nature of workflow applications and the performance requirements of the whole system. In this paper the architecture of distributed workflow execution is given, and the centralized model called CWF-net, which is based on colored Petri net, is presented. Based on the centralized model, a novel model fragmentation algorithm is proposed. This algorithm partitioned the centralized model into fragments by duplicating the places shared by transitions which are executed in different sites. The behavioral equivalence between the CWF-net and resulted fragments are guaranteed by the extended firing rules. Then the correctness of the fragmentation algorithm is discussed, the correctness criteria comprises completeness of the fragmentation, completeness of each fragment, and the behavioral equivalence after fragmentation. Finally the future research work is pointed out.

Component deployment within collaborative sessions is the process through which collaborative tools viewed as monolithic or composite components are made available to session members. Existing approaches dealing with this process adopt an offline exhaustive and static deployment technique. This kind of deployment is not applicable for collaboration where the session structure evolves in time and changes during the collaborative work. In this case, the component distribution is affected by session dynamics. Deploying components can be efficiently and correctly automated by using a formal session model based on collaboration graphs. In this paper, we introduce the problem of dynamic deployment for collaborative sessions, and we describe CDS, a first prototype system we have developed that supports both the initial and the subsequent deployment process according to a formal session model, while satisfying low-level constraints resulting from the heterogeneity of the target environment.

Despite the technological enhancement IT has had, some main points still have no satisfactory solutions and constitute a research subject for those interested in knowledge management. It does not seem evident that the adoption of either groupware technologies or collaborative environments induces effective collaborative/cooperative behavior in team workers. If some collaborative environment projects are strongly planned they have difficulty to be integrated in the workers’ daily habits. We assume that the problem may have two dimensions that shall be considered: a) the commonly accepted cycle of knowledge management is unable to cover the rich and complex cycle of social creation and validation of knowledge; b) a distributed environment architecture seems to be the best candidate to implement a system where the number, the complexity and the evolving characteristics of services that would take into account socio-interactionist dimensions of individuals and groups are necessary to reinforce collaborative behaviors. A Collaborative Online Learning Environment is discussed.