The main objective of this article is to introduce methods that aid the developer of an integrated system over overlapping, but contradicting sources in the task of improving the quality of data. Value conflicts between contradicting sources are often systematic, caused by some characteristic of the different sources. Our goal is to identify such systematic differences and outline data patterns that occur in conjunction with them. Evaluated by an expert user, the regularities discovered provide insights into possible conflict reasons and help to assess the quality of inconsistent values. The contributions of this article are two concepts of systematic conflicts: contradiction patterns and minimal update sequences.