Towards maintaining consistency of spatial databases

This paper focuses on the consistency issues related to integrating multiple sets of spatial data in spatial information systems such as Geographic Information Systems (GISs). Data sets to be integrated are assumed to hold information about the same geographic features which can be drawn from different sources at different times, which may vary in reliability and accuracy, and which may vary in the scale of presentation resulting in possible multiple spatial representations for these features. A systematic approach is proposed which relies first on breaking down the consistency issue by identifying a range of consistency classes which can be checked in isolation. These classes are a representative set of properties and relationships which can completely identify the geographic objects in the data sets. Different levels of consistency are then proposed, namely, total, partial and conditional, which can be checked for every consistency class. This provides the flexibility for two data sets to be integrated without necessarily being totally consistent in every aspect. The second step of the proposed approach is to explicitly represent the different classes and levels of consistency in the system. As an example, a simple structure which stores adjacency relationships is given which can be used for the explicit representation of topological consistency. The paper also proposes that the set of consistent knowledge in the data sets (which is mostly qualitative) be explicitly represented in the database and that uncertainty or ambiguity inherent in the knowledge be represented as well.