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Time and Relational Theory by Nikos Lorentzos, Hugh Darwen, C.J. Date

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Chapter 7

Interval Operators

This chapter introduces a convenient informal notation for points and intervals and for some of the most fundamental operators on such points and intervals: first, last, next, prior, BEGIN, END, PRE, POST, and so on. Using that notation, it then defines and illustrates a collection of generic comparison operators for intervals, known generically as Allen’s operators: interval equality, interval inclusion and proper inclusion, BEFORE and AFTER, OVERLAPS, MEETS, MERGES, and BEGINS and ENDS. Using these operators, the chapter then goes on to define interval analogs of the well known set theory operators UNION, INTERSECT, and MINUS. Finally, it shows how all of these operators can be used to help with the practical problem ...

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