Quote: tuples or values may be missing; either applicable, unknown, or inapplicable

Quotation Skeleton

Figure 8.1 Classification of Missing Information in a … [A tree diagram with MISSING as the root and WHOLE TUPLES and DB-VALUES as the middle layer. The leaves are, for WHOLE TUPLES, non-events, events not known to the DBMS, and inapplicable events, and for DB-VALUES, applicable (A-marked), inapplicable (I-marked), and other. ... [p. 172] … [A-marked] and missing-and-inapplicable [I-marked] appear to justify general support by the … A basic principle of the relational approach to … a mark (originally called a null or null …   Google-1   Google-2

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Additional Titles

Quote: use A-mark for missing-but-applicable values and I-mark for missing-but-inapplicable values; in place of null values

Related Topics

Topic: undefined, null, and other signal values (33 items)
Topic: database schema (29 items)