INGENS is a prototype of GIS which integrates a geographic knowledge discovery engine to mine several kinds of spatial KDD objects from the topographic maps stored in a spatial database. In this paper we describe the main principles of an inductive spatial database in INGENS. Inductive database allows to keep permanent KDD objects and integrate database technology with systems for the geographic knowledge generation. In contrast to traditional spatial database technology, inductive database allows to answer queries which require synthesizing and applying plausible knowledge which is generated by (inductive) inference from both spatial objects and KDD objects (prior knowledge) stored in the same database.