The spread of electronic use of data in various areas has pushed the importance of data quality to a higher level. Data quality has syntactic and semantic components; the syntactic component is relatively easy to achieve if supported by tools (either off-the-shelf or our own), while the semantic component requires more research. In many cases such data come from different sources, are distributed across enterprises and are at different quality levels. Special attention needs to be paid to data upon which critical decisions are met, such as medical data for example. The starting point for research is in our case the risk of the medical area. We focus on the semantic component of medical data quality.