Qualitative Spatial Reasoning

Physical space has unique properties which form the basis of fundamental capabilities of cognitive systems. This paper explores some cognitive aspects of perception and knowledge representation and explains why spatial knowledge is of particular interest for cognitive science. It is suggested that Ôspatial inference enginesÕ provide the basis for rather general cognitive capabilities inside and outside the spatial domain. The role of abstraction in spatial reasoning and the advantages of qualitative spatial knowledge over quantitative knowledge are discussed. The usefulness of spatial representations with a low degree of abstraction is shown. An example from vision (the aquarium domain) is used to illustrate in which ways knowledge about space may be uncertain or incomplete. Parallels are drawn between the spatial and the temporal domains. A concrete approach for the representation of qualitative spatial knowledge on the basis of Ôconceptual neighborhoodÕ is suggested and some potential application areas are mentioned. 1. What is special about spatial knowledge? Our knowledge about physical space differs from all other knowledge in a very significant way: we can perceive space directly through various channels conveying distinct modalities. Unlike in the case of other perceivable domains, spatial knowledge obtained through one channel can be verified or refuted by perception through the other channels. As a consequence, we are disproportionally confident about what we know about space: we take it for real. More specifically, we perceive spatial dimensions visually, tactily, acoustically, and even by smell and by temperature sensation. Some animals exploit perception of electrical or magnetic fields for spatial orientation. Within the visual sense, we obtain clues about space through size, brightness, hue, saturation, and texture information; within the acoustic sense, we obtain clues about space through loudness, frequency, and signal/noise ratio. In addition to perceiving space multimodally, we can modify spatial situations by moving objects, we can expose objects to the perceivable influence of physical forces, and we can modify our spatial perception by moving ourselves. In this way, we experience the laws of space as we can experience no other dimension. In contrast, the perception of other dimensions like color, visual brightness, sound, smell, temperature, etc. relies on single modalities and we cannot directly modify them. This makes the * Research supported by Deutsche Forschungsgemeinschaft under grants Br 609/4-2, Fr 806/1-1, and by Siemens AG.