Theoretical starting points and methods leading to the creation of a consistent database of thermodynamic properties of individual substances are given. The database is easy to modify and update. An exact definition of the concept consistent is given after all the relations and connections have been given. The proposed general methods are realized using computer programs and the species file, in which the thermodynamic properties of 326 gaseous and 34 condensed substances are stored that were prepared from a set of elements epsilon = {H, C, N, O, F, S, W, Ar, Ca, Cu, e(-1)}. Together with other files and programs the species file forms the database system TheCoufal, which is described in detail below, and stored as from the date of publication of this paper at the address http: //www.feec.vutbr.cz/similar to coufal/.