Entity and referential integrity are the most fundamental constraints that any relational database should satisfy. We re-examine these fundamental constraints in the context of incomplete relations, which may have null values of the types \value exists but is unknown" and \value does not exist". We argue that in practice the restrictions that these constraints impose on the occurrences of null ...

Negative associations between birth order and intelligence level have been found in numerous studies. The explanation for this relation is not clear, and several hypotheses have been suggested. One family of hypotheses suggests that the relation is due to more-favorable family interaction and stimulation of low-birth-order children, whereas others claim that the effect is caused by prenatal ges...

Men who had been in hospital for myocardial infarction (MI) were compared with other male patients in an attempt to provide evidence on the hypothesis linking MI with poverty in childhood followed by relative affluence. In each of three social class groupings MI patients came from larger families than controls, and a higher proportion of their fathers had been unemployed for more than a year du...

BACKGROUND The authors tested hypotheses that more noxious family environments are associated with poorer adult and child oral health. METHODS A community sample of married or cohabiting couples (N = 135) and their elementary school-aged children participated. Dental hygienists determined the number of decayed, missing and filled surfaces via oral examination. Subjective oral health impacts w...