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Dive into the research topics where Luca Forlizzi is active.

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Featured researches published by Luca Forlizzi.


international conference on management of data | 2000

A data model and data structures for moving objects databases

Luca Forlizzi; Ralf Hartmut Güting; Enrico Nardelli; Markus Schneider

We consider spatio-temporal databases supporting spatial objects with continuously changing position and extent, termed moving objects databases. We formally define a data model for such databases that includes complex evolving spatial structures such as line networks or multi-component regions with holes. The data model is given as a collection of data types and operations which can be plugged as attribute types into any DBMS data model (e.g. relational, or object-oriented) to obtain a complete model and query language. A particular novel concept is the sliced representation which represents a temporal development as a set of units, where unit types for spatial and other data types represent certain “simple” functions of time. We also show how the model can be mapped into concrete physical data structures in a DBMS environment.


The Computer Journal | 2003

Algorithms for Moving Objects Databases

José Antonio Cotelo Lema; Luca Forlizzi; Ralf Hartmut Güting; Enrico Nardelli; Markus Schneider

Whereas earlier work on spatiotemporal databases generally focused on geometries changing in discrete steps, the emerging area of moving objects databases supports geometries changing continuously. Two important abstractions are moving point and moving region, modelling objects for which only the time-dependent position, or also the shape and extent are relevant, respectively. Examples of the first kind of moving entity are all kinds of vehicles, aircraft, people or animals; of the latter hurricanes, forest fires, forest growth or oil spills in the sea. The goal is to develop data models and query languages as well as DBMS implementations supporting such entities, enabling new kinds of database applications. In earlier work we have proposed an approach based on


ifip world computer congress wcc | 2006

Reusing Optimal TSP Solutions for Locally Modified Input Instances

Hans-Joachim Böckenhauer; Luca Forlizzi; Juraj Hromkovič; Joachim Kneis; Joachim Kupke; Guido Proietti; Peter Widmayer

Given an instance of an optimization problem together with an optimal solution, we consider the scenario in which this instance is modified locally. In graph problems, e.g., a singular edge might be removed or added, or an edge weight might be varied, etc. For a problem U and such a local modification operation, let LM-U (local-modification-U) denote the resulting problem. The question is whether it is possible to exploit the additional knowledge of an optimal solution to the original instance or not, i.e., whether LM-U is computationally more tractable than U. Here, we give non-trivial examples both of problems where this is and problems where this is not the case. Our main results are these: 1. The local modification to change the cost of a singular edge turns the traveling salesperson problem (TSP) into a problem LM-TSP which is as hard as TSP itself, i.e., unless P=NP, there is no polynomial-time p(n)-approximation algorithm for LM-TSP for any polynomial p. Moreover, LM-TSP where inputs must satisfy the β triangle inequality (LM-Δ β -TSP) remains NP-hard for all β > 1/2. 2. For LM-Δ-TSP (i.e., metric LM-TSP), an efficient 1.4-approximation algorithm is presented. In other words, the additional information enables us to do better than if we simply used Christofides’ algorithm for the modified input. 3. Similarly, for all 1 < β < 3.34899, we achieve a better approximation ratio for LM-Δ β -TSP than for Δ’-TSP. 4. Metric TSP with deadlines (time windows), if a single deadline or the cost of a single edge is modified, exhibits the same lower bounds on the approximability in these local-modification versions as those currently known for the original problem. instance. A second construction inflates this advantage. Tours which start at time X, different from those that start between times X+g and X +ςg, may spend some extra time to visit a group of vertices which, unless visited early, will cause belated tours to run k times zigzag across a huge distance γ.


conference on current trends in theory and practice of informatics | 2005

On the stability of approximation for hamiltonian path problems

Luca Forlizzi; Juraj Hromkovič; Guido Proietti; Sebastian Seibert

We consider the problem of finding a cheapest Hamiltonian path of a complete graph satisfying a relaxed triangle inequality, i.e., such that for some parameter β > 1, the edge costs satisfy the inequality c({x, y}) ≤β (c({x, z}) + c({z, y})) for every triple of vertices x, y, z. There are three variants of this problem, depending on the number of prespecified endpoints: zero, one, or two. For metric graphs there exist approximation algorithms, with approximation ratio 3/2 for the first two variants and 5/3 for the latter one. Using results on the approximability of the Travelling Salesman Problem with input graphs satisfying the relaxed triangle inequality, we obtain for our problem approximation algorithms with ratio in(β 2 + β,3/2 β 2) for zero or one respecified endpoints, and 5/3 β2 for two endpoints.


international parallel and distributed processing symposium | 2003

Quality of service in wireless networks

Vittorio Bilò; A. Di Pasquale; Fabio Fioravanti; Michele Flammini; Luca Forlizzi; F. Lo Presti; Giovanna Melideo; Enrico Nardelli; Alfredo Navarra; Guido Proietti

In this paper we revise some of the most relevant aspects concerning the quality of service in wireless networks, providing, along the research issues we are currently pursuing, both the state-of-the-art and our recent achievements. More specifically, first of all we focus on network survivability, that is the ability of the network of maintaining functionality as a consequence of a component failure. Then, we turn our attention on data access and network services in a distributed environment. Finally, we analyze a basic network optimization task, that is routing design in wireless ATM networks.


symposium on large spatial databases | 2003

Region-based query languages for spatial databases in the topological data model

Luca Forlizzi; Bart Kuijpers; Enrico Nardelli

We consider spatial databases in the topological data model, i.e., databases that consist of a finite number of labeled regions in the real plane. Such databases partition the plane further into elementary regions. We propose a first-order language, which uses elementary-region variables and label variables, to query spatial databases. All queries ex- pressible in this first-order logic are topological and they can be evalu- ated in polynomial time. Furthermore, the proposed language is pow- erful enough to distinguish between any two spatial databases that are not topologically equivalent. This language does not allow the expression of all computable topological queries, however, as is illustrated by the connectivity query. We also study some more powerful extensions of this first-order language, e.g., with a while-loop. In particular, we describe an extension that is sound and computationally complete for the topological queries on spatial databases in the topological data model.


Archive | 2003

Chapter 6: Access Methods and Query Processing Techniques

Adriano Di Pasquale; Luca Forlizzi; Christian S. Jensen; Yannis Manolopoulos; Enrico Nardelli; Dieter Pfoser; Guido Proietti; Simonas Saltenis; Yannis Theodoridis; Theodoros Tzouramanis; Michael Vassilakopoulos

The performance of a database management system (DBMS) is fundamentally dependent on the access methods and query processing techniques available to the system. Traditionally, relational DBMSs have relied on well-known access methods, such as the ubiquitous B + -tree, hashing with chaining, and, in some cases, linear hashing [52]. Object-oriented and object-relational systems have also adopted these structures to a great extend.


Theory of Computing Systems \/ Mathematical Systems Theory | 2011

Approximating the Metric TSP in Linear Time

Davide Bilò; Luca Forlizzi; Guido Proietti

Given a metric graph G=(V,E) of n vertices, i.e., a complete graph with a non-negative real edge cost function satisfying the triangle inequality, the metricity degree of G is defined as


conference on current trends in theory and practice of informatics | 1998

Some Results on the Modelling of Spatial Data

Luca Forlizzi; Enrico Nardelli

\beta=\max_{x,y,z\in V}\{\frac{c(x,y)}{c(x,z)+c(y,z)}\}\in[\frac{1}{2},1]


international conference informatics schools | 2018

A Core Informatics Curriculum for Italian Compulsory Education

Luca Forlizzi; Michael Lodi; Violetta Lonati; Claudio Mirolo; Mattia Monga; Alberto Montresor; Anna Morpurgo; Enrico Nardelli

. This value is instrumental to establish the approximability of several NP-hard optimization problems definable on G, like for instance the prominent traveling salesman problem, which asks for finding a Hamiltonian cycle of G of minimum total cost. In fact, this problem can be approximated quite accurately depending on the metricity degree of G, namely by a ratio of either

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Enrico Nardelli

University of Rome Tor Vergata

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