P. Di Felice

Topological invariants for lines

A set of topological invariants for relations between lines embedded in the 2-dimensional Euclidean space is given. The set of invariants is proven to be necessary and sufficient to characterize topological equivalence classes of binary relations between simple lines. The topology of arbitrarily complex geometric scenes is described with a variation of the same set of invariants. Polynomial time algorithms are given to assess topological equivalence of two scenes. Invariants and efficient algorithms is due to application areas of spatial database systems where a model for describing topological relations between planar features is sought.

Browsing in geographic databases: an object-oriented approach

An interaction model for object-oriented geographic databases is presented. A browsing technique based on the model is outlined. The approach is uniform for navigating both the intensional and extensional part of the database. The proposed interaction model is flexible and is suitable for satisfying many purposes. It is able to satisfy users interested in getting a general idea about the contents of the database, as well as those with more specific tasks to accomplish. Depending on their requirements, users may control the degree of complexity of the information presented on the screen. Two basic criteria are adopted for browsing the database: logic adjacency and spatial adjacency between objects. Logic adjacency is determined by four conceptual links, while spatial adjacency is related to the two-dimensional (map-based) view of geographic entities.<<ETX>>

A JavaRMI-based application supporting interoperability in a GIS context

The growth of the Internet has emphasized the need for interoperability among different and heterogeneous systems, i.e. their ability to exchange data and services in a transparent way. The article addresses interoperability in a GIS context where systems, historically monolithics, need to exchange spatial data. The work is based on the models proposed by the OpenGIS Consortium, whose mission is the unification of spatial data models and services in order to achieve interoperability among GISs. The paper faces the problems connected with the interoperability at different levels of abstraction. At the highest level (the spatial data on the Internet), a set of common interfaces are adopted to represent both data and services; at the bottom level (database level), the concept of a specialized server (called OGIS/SQL server) is introduced which is the entity that tries to obtain data integration among the data sets. The paper also discusses an implementation of a JavaRMI-based application, that allows different and Web distributed data sets to be interconnected. The architecture of the application is made up of two different relational databases (one stores rivers and the other cities), a distributed object (representing the origin of its own spatial reference system), and a client that acquires (by query) spatial data from the previous mentioned spatial data sources, stores them in a local database and then visualizes the result.

A spatial data model underlying human interaction with object-oriented spatial databases

In geographic maps, objects are represented in a context extremely rich of relationships among them, either one-to-one or many-to-many. Unfortunately, all these relationships can not be directly represented in the database scheme. Nevertheless, it should be possible to show them to the user during the interaction. To manage this problem, the authors refer to a two-level database architecture with an object-oriented data model at the bottom level (the logic level), and an interaction model at the top level. The spatial data model given is an essential part of the interaction model. The spatial data model is a conceptual tool that enhances the object-oriented model with spatial relationships between objects. The basic objectives of the spatial data model are outlined: to point out the relationships among objects to be shown in the views, to define data structures suitable for navigating among database objects, and to provide a simple and powerful calculus for posing spatial queries against the database.<<ETX>>

Abstract data type and mathematical software reusability: two linked concepts

Experience with the design and implementation of a reusable Pascal code is reported. The project concerns the solution of the LU-factorization problem on large sparse matrices. The code carried out is structured into reusable units. The unit design strategy is based on the abstract data type (ADT) notion. As an example the interface of the FindPivot unit, of the LU factorisation program, is listed. >Experience with the design and implementation of a reusable Pascal code is reported. The project concerns the solution of the LU-factorization problem on large sparse matrices. The code carried out is structured into reusable units. The unit design strategy is based on the abstract data type (ADT) notion. As an example the interface of the FindPivot unit, of the LU factorisation program, is listed.<<ETX>>

An object-oriented conceptual model for the representation of geographic information

The interest of the DP community towards geographic databases is large. The drawbacks of traditional database systems when used for handling unstructured data have been largely pointed out in the literature. At present, research efforts are concentrated on the investigation of the usability of the object-oriented approach for developing a new generation of powerful geographic database systems. The complexity of geographic systems, in terms of relationships to be modelled and operations to be performed on data, is well-known; therefore a conceptual analysis of the specific situation is a good strategy for handling the complexity of the implementation. The authors propose an object-oriented conceptual model tailored for organizing and representing basic map elements and their relationships, as well as operations of interest for the management of geographic data. The aim is to provide designers with a conceptual tool useful for organizing their knowledge about a geographic application in terms of basic concepts of the object-oriented paradigm, namely classes, instances, and methods.<<ETX>>

Management of spatial data: basic issues and some solutions

The authors investigate the usability of the object-oriented paradigm to develop geographic applications, which involve an interesting category of spatial data. As a first step, abstract concepts such as map elements and their relationships are modeled. Specifically, a special kind of relationship (i.e. the conceptual link belongs-to) is proposed to model, in a uniform way, spatial properties concerning the intersection of two geographic elements (e.g. a river crosses a state), as well as the containment of a geographic area in another one (e.g. a country belongs to a continent). Then a large set of operations useful to manipulate geographic data is given according to existing literature. Finally, the authors propose a structure for objects (either classes or instances) specifically tailored for geographic applications.<<ETX>>

Multiparadigm query strategies in object-oriented geographic databases

The authors discuss three different paradigms suitable for querying object-oriented geographic databases. All together, the paradigms presented constitute the basis of a flexible and easy to use querying environment suitable for different categories of users. The first paradigm, to be adopted by programmer users, is based on the message sending mechanism of object-oriented database programming languages. The second paradigm is a browsing-based technique suitable for not unskilled users who have only a vague idea of the contents of the database. Finally, a frame-based approach is adopted for the third paradigm: this is suitable for non-programmer users who have a specific task to accomplish.<<ETX>>

An interaction environment supporting the retrievability of reusable software components

The card-based system presented is appropriate for supporting the reuse of code and test cases with respect to small size software projects. EasyCard is a system tailored for running on personal computers. Such a system provides the user with an easy to use interaction environment where the user can enter into and retrieve from a library information about available software components. Specifically, EasyCard features a screen-frame-based data acquisition facility, a graphical query language for retrieving information about software components, and, finally, a browsing environment suitable to explore the retrieved information. Visual feedback about the current status of the exploration prevents programmers disorientation.<<ETX>>

Use Case Double Tracing Linking Business Modeling to Software Development

Use cases are recommended as a powerful tool to carry out applications when moving from requirements analysis to design. In this contribution, we start from a recent software methodology that has been modified to pursue a strictly model-driven engineering approach. The work focuses on relevant elements of use cases in UML modeling, adapted and extended to support business modeling activities. Specifically, we introduce the idea of performing a “double tracing” between business modeling and system modeling: in this way a strong link between business requirements and the software solution to be developed is established.