Alberto Belussi

An authorization model for geographical maps

Access control is an important component of any database management system. Several access control models have been proposed for conventional databases. However, these models do not seem adequate for geographical databases, due to the peculiarities of geographical data. Previous work on access control models for geographical data mainly concerns raster maps (images). In this paper, we present a discretionary access control model for geographical maps. We assume that each map is composed of a set of features. Each feature is represented in one or more maps by spatial objects, described by means of different spatial properties: geometric properties, describing the shape, extension and location of the objects, and topological properties, describing the topological relationships existing among objects. The proposed access control model allows the security administrator to define authorizations against map objects at a very fine granularity level, taking into account the various spatial representations and the object dimension. The model also supports both positive and negative authorizations as well as different propagation rules that make access control very flexible.

From the conceptual design of spatial constraints to their implementation in real systems

The spatial data community recognizes the need for procedures that automatically validate spatial integrity constraints defined at conceptual level. This validation becomes particularly important in an open and distributed environment, like a Spatial Data Infrastructure (SDI), where the level of integration and interoperability is very high. However, the current gap between the conceptual design of a spatial database and its implementation into a GIS system makes the definition of spatial constraints useful only for documentation purposes and not for automatic validation. The GeoUML modeling language provides a set of predefined OCL templates for expressing the most common spatial constraints. In this paper, we deal with the validation problem by proposing a methodology for automatically translating the OCL constraints of GeoUML into SQL spatial queries, thus obtaining a platform independent general validation tool.

An ISO TC 211 conformant approach to model spatial integrity constraints in the conceptual design of geographical databases

The ISO TC 211 standards have defined a set of formal models for the conceptual modeling of spatial data using the Unified Modeling Language (UML) and the geometry approach adopted by the ISO spatial data model and by the Geographic Mark-up Language (GML). This approach aims to define a conceptual model for the design of geographic databases and for the geospatial interoperability of heterogeneous spatial databases. The ISO standards are however complex and counterintuitive in dealing with spatial integrity constraints, which are fundamental for the expressiveness of a conceptual model in the geographic application domain. This paper improves the ISO approach by proposing a framework which allows the definition of powerful, easy to use, and ISO conformant modeling abstractions for topological spatial constraints. These modeling abstractions have been incorporated in the definition of the GeoUML conceptual model used in the Italian IntesaGIS project for the definition of the “core” database of the Italian Spatial Data Infrastructure.

Spatial Data on the Web

Models for Representing Spatial Semistructured, Multiresolution, and Multiscale Data.- GeoMTGM: A Graphical Data Model for Semistructured, Geographical, and Temporal Data.- Out-of-core Multiresolution Terrain Modeling.- Progressive Techniques for Efficient Vector Map Data Transmission: An Overview.- Model Generalization and Methods for Effective Query Processing and Visualization in a WebService/Client Architecture.- Integration of Spatial Data Sources.- Automated Geographical Information Fusion and Ontology Alignment.- A Quality-enabled Spatial Integration System.- Using Qualitative Information in Query Processing over Multiresolution Maps.- Spatial Data Protection.- Access Control Systems for Geospatial Data and Applications.- Secure Outsourcing of Geographical Data Over the Web: Techniques and Architectures.- Information Hiding for Spatial and Geographical Data.- Innovative Applications for Mobile Devices.- Geographical Data Visualization on Mobile Devices for Useers Navigation and Decision Support Activites.- Tracking of Moving Objects with Accuracy Guarantees.- Spatial Data on the Web: Issues and Challenges.- Spatial Data on the Web: Issues and Challenges.

Towards similarity-based topological query languages

In recent times, the proliferation of spatial data on the Internet is beginning to allow a much larger audience to access and share data currently available in various Geographic Information Systems (GISs). Unfortunately, even if the user can potentially access a huge amount of data, often, she has not enough knowledge about the spatial domain she wants to query, resulting in a reduction of the quality of the query results. This aspect is even more relevant in integration architectures, where the user often specifies a global query over a global schema, without having knowledge about the specific local schemas over which the query has to be executed. In order to overcome such problem, a possible solution is to introduce some mechanism of query relaxation, by which approximated answers are returned to the user. In this paper, we consider the relaxation problem for spatial topological queries. In particular, we present some relaxed topological predicates and we show in which application contexts they can be significantly used. In order to make such predicates effectively usable, we discuss how GQuery, an XML-based spatial query language, can be extended to support similarity-based queries through the proposed operators.

A Framework for Managing Temporal Dimensions in Archaeological Data

Time and space are two important characteristics of archaeological data. As regards to the first aspect, in literature many time dimensions for archaeology have been defined which extend from the excavation time, to the dating of archaeological objects. Standard ISO 19018 describes temporal characteristics of geographical information in terms of both geometric and topological primitives. The first aim of this paper is to analyze the applicability of such Standard for representing archaeological data, referring to the model adopted by the city of Verona (Italy) as case study. However, since archaeological dates are often subjective, estimated and imprecise, one of the main lack in the Standard is the inability to incorporate such vagueness in date representation. Therefore, the second contribution of this paper is the extension of the Standard in order to represent fuzzy dates and fuzzy relationships among them. Finally, considering the process through which objects are usually manually dated by archeologists, some existing automatic techniques for time reasoning may be successfully applied in this context in order to guide the dating process. For this purpose, the last paper contribution regards the translation of some archaeological temporal data into a Fuzzy Temporal Constraint Network (FTCN) for checking the overall data consistency and reducing the vagueness of some dates based on their relationships with other ones.

Modelling Spatial Whole–Part relationships using an ISO-TC211 conformant approach

Abstract The important role of Spatial Whole–Part relationships in spatial database design is widely recognized and several researches have proposed specific spatial models to classify these relationships and their related topological constraints. The recent ISO-TC211 standards have defined a spatial data model and its use in spatial database design. However, the modelling of topological constraints of Spatial Whole–Part relationships requires additional complex and counterintuitive expressions specified by using a formal constraint language. This paper shows the complexity of modelling Spatial Whole–Part relationships in ISO and proposes an approach for the definition of ISO conformant modelling abstractions which hide this kind of complexity to the database designer. This approach is applied to the definition of the modelling abstractions for Spatial Whole–Part relationships which cover all the Spatial Whole–Part relationships proposed in the literature.

Automatic updating of urban vector maps

In this paper we propose an automatic updating system for urban vector maps that is able to detect changes between the old dataset (consisting of both vector and raster maps) and the present time situation represented in a raster map. In order to automatically detect as much changes as possible and to extract vector data for new buildings we present a system composed of three main parts: the first part detects changes between the input vector map and the new raster map (based on edge matching), the second part locates new objects (based on color segmentation), and the third part extracts new objects boundaries to be used for updating the vector map (based on edge detection, color segmentation and adaptive edge linking). Experiments on real datasets illustrate the approach.

An integrity constraints driven system for updating spatial databases

This paper describes a prototypal system which has been implemented in order to explore the possibility of using topological integrity constraints as interactive drivers to support spatial database updates. The idea of using constraints to drive updates is applied also in traditional (non-spatial) databases; for example, in order to preserve referential integrity, the user can be forced to select a value in a given set, instead of permitting him to write an arbitrary value and then checking that the value satisfies the constraint. This idea seems to be much more relevant in spatial databases, both because spatial data possesses a much richer set of constraints, and because spatial updates are more complex and error-prone than traditional, alphanumeric updates. The paper first defines formally a rather general spatial database environment with integrity constraints, then describes a prototypal system which has been built in order to explore the practical effectiveness of the general idea (the feasibility includes performance, because the constraints are used during the interaction with the user). The prototype which has been implemented is capable of driving updates on simple polygons and uses a restricted class of integrity constraints; however, it is sufficiently powerful to demonstrate the feasibility of the approach.

Designing an urban-scale auditory alert system

The high tides that periodically flood Venice, locally known as acqua alta, are becoming more serious due to recent changes in the surrounding lagoon as well as atmospheric conditions. A special office of the Municipality of Venice, the Center for Tide Prediction and Warning (Centro Previsioni e Segnalazioni Maree-CPSM), provides a continuous tide forecast based on computational models as well as astronomical and meteorological data. When a significant high tide is expected, city authorities activate a network of electromechanical sirens for a few minutes, usually anticipating the tide peak by a few hours. The sirens, however, emit threatening wails reminiscent of air attack warnings, do not convey the gravity of the threat, and may not reach isolated or distant areas. Drawing on a wide range of computing technologies and methodologies, the authors present a new auditory alert system for high tides in Venice designed to replace the existing network of electromechanical sirens. As part of this research effort, our project team first analyzed the current alert system using off-the-shelf acoustic simulation software and a specially designed visualization tool. We then used a form of constraint logic programming to determine the optimal placement of loudspeakers in Venice, a complex task with many physical, economic, and social constraints. Next, we created the alert sounds for our demanding listening environment. The final phase of the project involved iteratively validating and redesigning the alert signals using human testing.