Abstract The paper investigates possibilities of writing programs with having the relevant knowledge on programing available in explicity form, in order to perform experiments, a knowledge base was built which codes some of the knowledge related to the problem of selecting a proper data type in the process of program formation. The base is presented in paper along with one experiment which also shows the system performance and user-system interaction. The experiment setting is such that the user makes a guess which data type is appropriate to use and this hypothesis is either confirmed or rejected by the system. Moreover, as a result of the system’s deductive reasoning other acceptable data types are proposed by the system. The result shows that the system is able to provide an advice to a programer. This can be particularly useful in the process of learning programing.