On a hierarchy of file types and a tower of their theories

Abstract

We present here a general method of software development which uses both: algorithmic logic and object programming. The approach will be presented in the form of a case study.

We discuss a rich system of files wich contains files of various types: text files, direct access files and binary sequential files. By introducing certain hierarchy one can gain a clear insight into the properties of files. A data structure of plain files is factorized out as a common factor of all mentioned types. All types of files are fully axiomatized in corresponding algorithmic theories. These theories form a tower since all of them are extensions of the theory of plain files.

Finally, one can construct a hierarchy of types which reflects the structure of the tower. In this way one obtains quite complicated software together with the clear specification of its functions. We hope that the reader will see the other applications of the general method presented here.

The research was supported by Polish Ministry of National Education, grant RP.I.09 (1990) and by French Ministere d'Education Nationale grant for LITA Pau. (1991)