Filippo Cacace

Integrating object-oriented data modelling with a rule-based programming paradigm

LOGRES is a new project for the development of extended database systems which is based on the integration of the object-oriented data modelling paradigm and of the rule-based approach for the specification of queries and updates. The data model supports generalization hierarchies and object sharing, the rule-based language extends Datalog to support generalized type constructors (sets, multisets, and sequences), rule-based integrity constraints are automatically produced by analyzing schema definitions. Modularization is a fundamental feature, as modules encapsulate queries and updates, when modules are applied to a LOGRES database, their side effects can be controlled. The LOGRES project is a follow-up of the ALGRES project, and takes advantage of the ALGRES programming environment for the development of a fast prototype.

An observer for a class of nonlinear systems with time varying observation delay

Abstract This paper presents a state observer for drift observable nonlinear systems when output measurements are affected by a known and bounded time varying delay. The structure of the proposed observer is very simple and it is a generalization of an existing observer for undelayed systems. The observer exhibits good performance in estimating the system state also in the presence of significant measurement delays. The technique used to prove the asymptotical convergence to zero of the observation error, based on the Lyapunov–Razumikhin approach, does not require any assumption about the dependence of the delay on the time.

Vertical handoff performance in heterogeneous networks

We study the problem of handoffs in heterogeneous (both wired and wireless) networks. We first present a testbed that integrates multiple network technologies (Ethernet LAN, WiFi and GPRS cellular data network) to provide seamless connectivity to mobile hosts. We then propose a model to analyze the performance of vertical handoffs as well as experimental measures to validate the model. Finally, we discuss the advantages of handoff detection and triggering through link layer mechanisms. An implementation of handoffs? link layer triggering is presented, and its performance is compared with layer-3 handoff triggering.

Seamless internetworking of WLANs and cellular networks: architecture and performance issues in a Mobile IPv6 scenario

We review the problem of network mobility and internetworking between heterogeneous data networks and present an approach to the integration of WLAN and cellular networks based on loose coupling and the use of emerging mobility protocols. The handoff performance of such an approach is studied, at the network and transport levels, in a realistic scenario along with the impact on global performance of transport protocols. Finally, a method of eliminating any packet loss at the network layer during handoff is presented and evaluated.

Managing mobility and adaptation in upcoming 802.21 enabled devices

One emerging characteristic of electronic devices is the increasing number of connectivity interfaces (aka NICs1) towards the outside world. That obviously translates in a set of technical issues related to their management in order to provide seamless connectivity when the connections move from one interface to another. The IEEE 802.21 is a recent effort of IEEE that aims at providing a general interface for the management of NICs. In this paper we discuss how the upcoming standard may be effectively exploited in a mobile context in order to hide network heterogeneity to end users. To accomplish this task, we propose a centralized element called Mobility Manager interfacing with the 802.21 sublayer and responsible for the application of connectivity policies. Based on a real testbed, we showed that the new standard and the MM can be used to improve network performance experienced by the end user. Moreover we showed how the MM can interact with adaptive applications in order to improve further the range of usability of real-time applications.

A CHAIN OBSERVER FOR NONLINEAR SYSTEMS WITH MULTIPLE TIME-VARYING MEASUREMENT DELAYS ∗

This paper presents a method for designing state observers with exponential error decay for nonlinear systems whose output measurements are affected by known time-varying delays. A modular approach is followed, where subobservers are connected in cascade to achieve a desired exponential convergence rate (chain observer). When the delay is small, a single-step observer is sufficient to carry out the goal. Two or more subobservers are needed in the the presence of large delays. The observer employs delay-dependent time-varying gains to achieve the desired exponential error decay. The proposed approach allows to deal with vector output measurements, where each output component can be affected by a different delay. Relationships among the error decay rate, the bound on the measurement delays, the observer gains, and the Lipschitz constants of the system are presented. The method is illustrated on the synchronization problem of continuous-time hyperchaotic systems with buffered measurements.

Analysis and experimentation over heterogeneous wireless networks

Wireless and mobile networks represent an enabling technology for ubiquitous access to information systems. However, there are critical issues that still prevent the widespread use of these technologies. In this paper we analyze and discuss our experience over a real ubiquitous network testbed capable to provide a seamless hand-off among heterogeneous networks. We describe Mobile IPv6/IPv4 interoperability and an efficient mechanism, based on link-layer information, for a seamless handoff among wired and wireless networks. We present the solutions adopted in setting up a real testbed and provide an evaluation of the observed performance, including a characterization of interoperability among three wireless access network technologies: 802.11 WLAN, GPRS, and UMTS.

A survey of parallel execution strategies for transitive closure and logic programs

An important feature of database technology of the nineties is the use of parallelism for speeding up the execution of complex queries. This technology is being tested in several experimental database architectures and a few commercial systems for conventional select-project-join queries. In particular, hash-based fragmentation is used to distribute data to disks under the control of different processors in order to perform selections and joins in parallel. With the development of new query languages, and in particular with the definition of transitive closure queries and of more general logic programming queries, the new dimension of recursion has been added to query processing. Recursive queries are complex; at the same time, their regular structure is particularly suited for parallel execution, and parallelism may give a high efficiency gain. We survey the approaches to parallel execution of recursive queries that have been presented in the recent literature. We observe that research on parallel execution of recursive queries is separated into two distinct subareas, one focused on the transitive closure of Relational Algebra expressions, the other one focused on optimization of more general Datalog queries. Though the subareas seem radically different because of the approach and formalism used, they have many common features. This is not surprising, because most typical Datalog queries can be solved by means of the transitive closure of simple algebraic expressions. We first analyze the relationship between the transitive closure of expressions in Relational Algebra and Datalog programs. We then review sequential methods for evaluating transitive closure, distinguishing iterative and direct methods. We address the parallelization of these methods, by discussing various forms of parallelization. Data fragmentation plays an important role in obtaining parallel execution; we describe hash-based and semantic fragmentation. Finally, we consider Datalog queries, and present general methods for parallel rule execution; we recognize the similarities between these methods and the methods reviewed previously, when the former are applied to linear Datalog queries. We also provide a quantitative analysis that shows the impact of the initial data distribution on the performance of methods.

A New Approach to Design Interval Observers for Linear Systems

Interval observers are dynamic systems that provide upper and lower bounds of the true state trajectories of systems. In this work we introduce a technique to design interval observers for linear systems affected by state and measurement disturbances, based on the Internal Positive Representations (IPRs) of systems, that exploits the order preserving property of positive systems. The method can be applied to both continuous and discrete time systems.

Exponential stabilization of linear systems with time-varying delayed state feedback via partial spectrum assignment

Abstract We consider the problem of controlling a linear system when the state is available with a known time-varying delay (delayed-state feedback control) or the actuator is affected by a delay. The solution proposed in this paper consists in partially assigning the spectrum of the closed-loop system to guarantee the exponential zero-state stability with a prescribed decay rate by means of a finite-dimensional control law. A non conservative bound on the maximum allowed delay for the prescribed decay rate is presented, which holds for both cases of constant and time-varying delays. An advantage over recent and similar approaches is that differentiability or continuity of the delay function is not required. We compare the performance of our approach, in terms of delay bound and input signal, with another recent approach.