Time and Relational Theory, 2nd Edition

Appendix C

Generalizing PACK and UNPACK

This appendix shows how the PACK and UNPACK operators can usefully be generalized to deal not just with sets of intervals as such but also with other kinds of sets—in particular, sets of relations, sets of sets, and sets of bags. The important special case of packing a relation on a relation valued attribute is considered in some detail.

Keywords: gneralized UNPACK; generalized PACK; unpacked form; packed form

All generalizations are dangerous (often quoted in the form All generalizations are false).

—Alexandre Dumas fils (attrib.)

In Chapter 8, we introduced the operators EXPAND and COLLAPSE and considered their effect on sets of intervals specifically. But we did also note the point in passing that there’s ...