Geological Data Model and cartographic representation: the CARG project experience

At the end of the eighties the Italian National Geological Survey (SGN) started to carry out a new geological and thematic cartographic project at a scale of 1:50.000 (CARG Project). Together with the field survey and mapping, the building of a digital database has been considered a topic of primary importance. The SGN proposed some guide lines in order to obtain homogenous products in terms of contents of the database and their cartographic representation. The challenge for this project is to find a way to collect, store, manage and retrieve large volumes of current and historical geological data sets. The recent advantages of the GIS technology have played an important role in order to reach and go beyond the project goals. This paper describes some of the preliminary design ideas related to the definition of a geological data model for the CARG project. This work looks for the creation of a solution to a complex problem: the need to manage diverse geological information in an object-relational database management system. In fact, exploiting the capabilities of this new system it has been possible to accommodate and, at the same time, implement the originally proposed database structure (by SGN) in order to obtain both an effective and flexible data model (designed to contain a broad array of geological information), and an automatic cartographic representation of the georeferenced data. The Computer-Aided Software Engineering (CASE) tools subsystem has been used to create the model of the structure of the geodatabase and, optionally, to generate code to define custom behaviour, using a graphical language - the Unified Modeling Language (UML). By means of class diagrams, it is possible to represent "geological objects" with a number of characteristics defining how they "work" and interact: behaviours, attribute domains, validation rules, topological and associative relationship rules. UML model has been created using specialized tools, such as Microsoft Visio®. Once the schema has been generated, it has been populated using existing geological data derived from the CARG Project. The experimental procedure involved in conducting the GIS project is completely implemented within a commercial software (ESRI® ArcGIS(TM)) in which the possibility to develop new applications has also been exploited.