Validating the contribution of real world knowledge to the diagnostic performance of automated database design tools diagnosis Automated database design tools that employ knowledge-based systems technology have the capability of providing intelligent support to humans during the process of database analysis and design. However, the capacity of these tools to simulate the diagnostic capabilities of human designers when performing a design task by making use of their knowledge of the real world remains a question. Therefore, in recent years there have been a number of attempts to develop tools that are capable of exploiting such real-world knowledge. It has been claimed that the use of such knowledge has the potential to increase the diagnostic performance of automated database design tools. However, to date little if any formal exploration and validation of this claim has taken place. This paper presents the work on exploring and validating the implications of exploiting three approaches proposed to facilitate the use and exploitation of real-world knowledge to the aspects of diagnostic performance of database design tools. Results obtained have demonstrated that the improvement of certain aspects of the diagnostic performance have been achieved.