I have invented the term "physical locator" to cover things like the
classic hardware pointers you are talking about, row_id within a table
structure, hash table values, etc. Anything that:
- Is not an attribute in the reality of the data model. in the
Relational keys are a set of attributes by definition. Nothing to do
with physical storage.
- They are generated inside the machine and depend on the internal
state of the machine at creation time. Nothing to do with the data
model or the real world.
And I do believe in duplicate values, but not duplicate data elements.
So did Dr. Codd when he introduced a "Degree of Duplication" operation
in his second version of RM. Codd also defined a surrogate as being
hidden from users, so things like auto-numbering and IDENTITY do not
qualify in most products.
Received on Thu Dec 22 2005 - 12:37:04 CST
