A Tool for Analyzing and Fixing Infeasible RCTA Instances

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Abstract

Minimum-distance controlled tabular adjustment methods (CTA), and its restricted variants (RCTA), is a recent perturbative approach for tabular data protection. Given a table to be protected, the purpose of RCTA is to find the closest table that guarantees protection levels for the sensitive cells. This is achieved by adding slight adjustments to the remaining cells, possibly excluding a subset of them (usually, the total cells) which preserve their original values. If either protection levels are large, or the bounds for cell deviations are tight, or too many cell values have to be preserved, the resulting mixed integer linear problem may be reported as infeasible. This work describes a tool developed for analyzing infeasible instances. The tool is based on a general elastic programming approach, which considers an artificial problem obtained by relaxing constraints and bounds through the addition of extra elastic variables. The tool allows selecting the subset of constraints and bounds to be relaxed, such that an elastic filter method can be applied for isolating a subset of infeasible table relations, protection levels, and cell bounds. Some computational experiments are reported using real-world instances.

Supported by grants MTM2009-08747 of the Spanish Ministry of Science and Innovation, SGR-2009-1122 of the Government of Catalonia, and Eurostat framework contract 22100.2006.002-226.532.