In the context of the GeoUML methodology the vision of Spatial Data Infrastructure (SDI) that is considered has been widely accepted in literature; in particular it is based on the following 6 reference principles in accordance with the INSPIRE European Directive:
- Data have to be collected only once and managed where it can be done in the more efficient way.
- It should be feasible to combine data coming from different sources and to share them among several users and applications.
- It should be feasible to share information that have been collected at different levels of details.
- Spatial data that are necessary for the territory government should exist and be widely accessible.
- It should be straightforward to identify which spatial data are available, to evaluate their effectiveness for your own goals and the conditions for obtaining and using them.
- Spatial data have to be easy to understand and interpreting using visualization tools.
By considering the approaches that have been applied by different public bodies in several countries, it makes sense to classify the SDI in two categories, that are different but not unable to coexist: i) the SDI for broadcast access and ii) the highly coupled SDI.
- In the SDI for broadcast access the emphasis is on the usability of spatial data, focusing on the principles 2, 3, 5 and 6 of INSPIRE. The main tools that are adopted in this type of SDI are the Geo-Portals; their focus is on metadata and accessibility.
- In the highly coupled SDI the emphasis is on the production and management of spatial data, with the aim to obtain (principles 1 and 4 of INSPIRE) that data that are necessary for the territory government, are effectively collected and updated by the most suitable subjects and harmonized among them (principles 2 and 3 of INSPIRE). A highly coupled SDI is an infrastructure that produces and maintains, through the cooperation of a set of variable but well defined public bodies, a distributed databases, that integrates in a consistent way the spatial information that is significant and of adequate quality for achieving the goals of the bodies themselves. In this type of SDI the emphasis is on the processes of data production and update, the quality certification and the applicative cooperation.