In analyzing and debugging data transformations, or more specifically relational queries, a subproblem is to understand why some data are not part of the query result. This problem has recently been addressed from different perspectives for various fragments of relational queries. The different perspectives yield different, yet complementary explanations of such missing-answers.
No takes yet. Share an insight, caveat, or question.
Melanie Herschel (2013) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: