Improving XML Data Quality with Functional Dependencies

We study the problem of repairing XML functional dependency violations by making the smallest value modifications in terms of repair cost. Our cost model assigns a weight to each leaf node in the XML document, and the cost of a repair is measured by the total weight of the modified nodes. We show that it is beyond reach in practice to find optimum repairs: this problem is already NP-complete for a setting with a fixed DTD, a fixed set of functional dependencies, and equal weights for all the nodes in the XML document. To this end we provide an efficient two-step heuristic method to repair XML functional dependency violations. First, the initial violations are captured and fixed by leveraging the conflict hypergraph. Second, the remaining conflicts are resolved by modifying the violating nodes and their related nodes called determinants, in a way that guarantees no new violations. The experimental results demonstrate that our algorithm scales well and is effective in improving data quality.