Re: Objects and Relations
Date: 14 Feb 2007 05:12:54 -0800
Message-ID: <1171458774.173578.146430_at_m58g2000cwm.googlegroups.com>
[Snipped crap from Keith Duggar]
> Nevertheless, for the benefit of other readers if nothing else, let me
> 1) Lego blocks are /not/ the same. They always have a different
> state that Keith has hit the nail on the head.
No. Keith has just once shown more misunderstanding of RM and
arrogance.
> location attribute.
BS. LegoBlock are indeed the same if they are to be a relation.
Stating that location attribute is a primary natural key for a LegoBlock is arbitrary and does not reflect the reality of LegoBlocks. Imagine a M:N cardinality between LegoBlock and Location Entity. In that case LocationEntity has a natural identifier (X, Y, Z). The natural identifier of a lego block could be a combination of its shape, color but certainly not its location.
> 2) Hence their x,y,z position attribute always identifies them.
False.
> 3) However this identifer is very hard to record and keep track of,
> even though it exists.
In the mind of people which pointer's obsessed maybe...
There is nothing complex about the identifier of a location is a
concatenation of XYZ and a referential.
> 4) So we represent it with a surrogate identifer (which is hence just
> an 'untrackable' attribute or, as others refer to it, an unfamiliar
> attribute).
In other words, Surrogate identifier has only the advantage of being
*familiar*.
> 5) OID's are hence not needed, and everything is just a value, as it
> should be.
OID = Implementation of Surrogate Key IF AND ONLY IF
--> unicity contraint has been implemented on the implementation of
the natural key
--> unicity constraint implemented on the OID
--> contraint of cardinality implemented 1:1 between the
implementation of the natural key and the OID....
In other words, almost never happens...
> 6) When I finally understood this (and it was a hard mental slog to
> shake off my OO mindset) I found it quite revelationary to my
> perspective on data management.
Guess we all went through this at some point in time...
[rest snipped] Received on Wed Feb 14 2007 - 14:12:54 CET