Note: To demonstrate the correctness and stability offered by a sound theoretical foundation (relative to the industry's fad-driven "cookbook" practices), I am re-publishing as "Oldies But Goodies" material from the old (2000-06) DBDebunk.com, so that you can judge for yourself how well my arguments hold up and whether the industry has progressed beyond the misconceptions those arguments were intended to dispel. I may revise, break into parts, and/or add comments and/or references, which I enclose in square brackets).
CLARIFICATIONS ON A DISCUSSION OF MY BOOK PART 2
(originally posted 2/21/01)
In Part 1 debunked a review of my book @Slashdot.Org. In parts 2-5 I tackled the discussion generated there by the review. In this last part I focus on the discussion of data hierarchies covered in chapter 7 of my book [the in-vogue re-emergent graph fad].
“Chapter 7 discusses data hierarchies and trees. In a nutshell: there are no trees in SQL. The author is distressed by this. Given that a foreign key is basically a pointer, you can store trees in databases, it might not be pretty and there may not be easy way to read them and it might not be a good thing to do - but if you feel the need then get right in there. Of course I could be totally wrong about this.”Confusing keys with pointers is one of the major errors many practitioners make ]. One intentional core advantage of the RDM is precisely that it prohibits pointers -- both physical and, as in object-orientation, logical. Exposing pointers to users has caused many unnecessary problems and complications, but offered no benefit (Don't Mix Pointers and Relations and Don't Mix Pointers and Relations - Please! in Date's RELATIONAL DATABASE WRITINGS 1994-1997). There is an easy way to demonstrate that relational keys are not, like object IDs (OID), pointers, but values: they represent uniquely identifying names/attributes of rel world entities. Pointers are system-generated internals and have no real world counterpart. The desirability of a data model that produces logical models that are faithful representations of the real world, without adding artifacts of their own. Indeed, as Date points out in Why The Object Model' is Not a Data Model in his above-mentioned book, the fact that "in the object world all the references to objects are by means of their corresponding OIDs explains why -- as is well known -- OO systems typically provide (a) two different equality comparison operators, equal OID vs. equal value and (b) two different assignment operators, assign OID vs. assign value. Note the added complication -- what is the benefit?