Strongly Possible Functional Dependencies for SQL

Missing data is a large-scale challenge to research and investigate. It reduces the statistical power produces negative consequences that may introduce selection bias on data. Many approaches handle this problem have been introduced. The main suggested are either missing values be ignored (removed) or imputed (filled in) with new values. This paper uses second method. Possible worlds possible certain keyswere introduced in Köhler et.al., by Levene et.al. Link functional dependencies (c-FD) as natural complement Lien's class of (p-FD). Weak strong were studied Loizou. We intermediate concept strongly obtained imputing already existing table preceding paper. results keys (spKey's) (spFD's). give polynomial algorithm verify single spKey show general, it NP-complete an arbitrary collection spKeys. graph-theoretical characterization validity given spFD X →sp Y.We show, complexity dependency then we some cases when verifying can done time.As step forward axiomatization spFD's, rules for weak checked. Appropriate weakenings those not sound spFD's listed. interaction between spKey's studied. Furthermore, graph theoretical implication singular attribute given.