Re: Identity modelling (was: dbdebunk 'Quote of Week' comment)


"mAsterdam" wrote:
> Alexandr Savinov wrote:
[snip]

> > - Identity cannot be considered without its scope. For example, a
> > physical address is retricted by the scope of one computer, a primary
> > key might be restricted by one database etc.

Agreed.

> >
> > - Logical/physical is a relative characterization rather than absolute.
> > Memory handle is really physical for an application program that uses
> > it, but it is logical for operating system w.r.t. to absolute offsets
> > in physical memory (offset may change while memory handle does not
> > change). In this sense all those disputes about lgoical/physical are
> > meaningless without specifying the context. Primary key may well be
> > viewed as a physical identifier from the point of view of some higher
> > level identification mechanism, say, global id. This means that global
> > id is permanent while primary key it substitues may change.

Agreed.

There are multiple levels of abstraction, and what is logical at one level
is physical at another.


One interesting case is that of the URL. Is a URL a key or a pointer? Does
it name the resource, or does it locate the resource?


.

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