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The New Relational Database Dictionary by C.J. Date

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Footnotes

Introduction

1 Actually the Manifesto itself has been revised and clarified somewhat since the Manifesto book was first published. The current version can be found in that same Explorations book.
2 Like The Third Manifesto itself, the Manifesto model of inheritance is revised and extended in the Explorations book.

Part II Inheritance

1 Note, however, that (e.g.) values of type ELLIPSE are really ellipses at some specific location in two-dimensional space; in other words, ellipses that occupy different positions in space but are otherwise identical are assumed for the sake of the example to be distinct (and similarly for rectangles, circles, etc.). Analogous remarks apply to Figs. 3-5 as well.
2 For the sake of the example, ellipses are assumed always to have their major axis horizontal and their minor axis vertical, so that A, B, and CTR are indeed sufficient to serve as a possrep.

Part III Intervals

1 In the context of an SQL period, however (see period), such symbols typically denote TO values.
2 As a matter of fact there’s an analogous constraint from S_STATUS_DURING to S_DURING as well, and the two foreign U_key constraints can therefore be combined into a U_equality dependency, q.v. See foreign U_key for futher discussion.

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