A file structure for semantic databases

• The entities of the real world are represented in the database in a manner invisible to the user. (Unlike that, in the relational model the entities are represented by the values of keys of some tables; in the network model the entities are represented by record occurrences.) Hereinafter, the user-invisible representations of real-world entities are referred to as "abstract objects". The "concrete objects", or "printable values", are numbers, character strings, etc. The concrete objects have conventional representations on paper and in the computer.