ApproxMap - a method for mapping blank nodes in RDF datasets

Abstract

Background: Versioning has proven to be essential in areas like software development or data and knowledge management. For systems or applications making use of documents formatted according to the Resource Description Framework (RDF) standard, it is difficult to calculate the difference between two versions, owing to the presence of blank nodes, also known as bnodes in RDF graphs. These are anonymous nodes that can assume different identifiers between versions. In this case, the challenge lies in finding a mapping between the sets of blank nodes in the two versions while minimizing the operations needed to convert one version into another. Methods: Within this context, we propose an algorithm, named ApproxMap, for mapping bnodes based on extended concepts of rough set theory, which provides a way to measure the proximity of bnodes and map them with closer approximations. Our heuristic method considers various strategies for reducing both the number of comparisons between blank nodes and the delta between the compared versions. The proposed algorithm has a worst-case time complexity of O(n 2). Results: ApproxMap showed satisfactory performance in our groups of experiments, as the algorithm that obtained solutions closest to the optimal values. This algorithm succeeded in finding the optimal delta size in 59% of the tests involving optimal values. ApproxMap achieved a delta size smaller than or equal to those of existing algorithms in at least 95% of the tested cases. Conclusions: The results show that the proposed algorithm can be successfully applied to versioning RDF documents, such as that produced by software processes with iterative and incremental development. We recommend applying ApproxMap in various situations, particularly those involving similar versions and directly connected bnodes.