We denote a relation expression by r i and the whole set of relation expressions by D. We call a subset of relation expressions which manifest, directly or indirectly, a relation R, as the manifestation set of R. A relation, R, is characterized by the two sets, the extension set and the manifestation set.
the two sets are implicitly associated with each other via the relation R. This association between the two sets constitutes the foundation of the common semantic space to be constructed in this paper.