One of the most important issues in the multidatabase research is semantic heterogeneity in autonomous databases. The authors propose a new model for realizing semantic interoperability among data items in multidatabase systems. In multidatabase systems, it is not easy to select appropriate databases and extract significant information for user's requests from many databases which are managed independently by its own database management system. One of the hardest problems is that it is difficult to judge equivalence or similarity between data items which are included in different databases. To select appropriate databases and extract significant information for user's requests, they have designed a meta database system. In this system. a mathematical model of meaning is used to find different data items with the equivalent or similar meaning or to recognize the different meanings of a data item. The mathematical model of meaning consists of: (1) defining a normal space, (2) constructing a class of projections which represents a phase of meaning, (3) constructing a mechanism to select a subspace of the normed space according to the context. The main feature of this model is that the specific meaning of a data item can be recognized disambiguously and dynamically according to the context.