Re: One-To-One Relationships

From: David Cressey <>
Date: Fri, 30 Nov 2007 13:33:55 GMT
Message-ID: <7jU3j.20656$Mg1.9162_at_trndny03>

"paul c" <> wrote in message news:HIK3j.74278$cD.9309_at_pd7urf2no...
> JOG wrote:
> ...
> >
> > There are a load of atoms. Someone else looks at them and says hey its
> > a dead bit of wood, its a 'stump' entity. Someone else considers a
> > bigger picture and says its a snapshot of a 'tree' entity. Me, being
> > lazy, say hey I could sit on that, its a 'seat' entity, etc., ad
> > infinitum.
> > ...
> (Not trying to be a smart-ass): By your definition, could the orbits of
> electrons be database entities? Could a number be an entity? Could a
> legal entity that is owned by another legal entity be an entity in the
> same sense as a number could be?

(not trying to respond like a smart-ass): The distinction between "the database" and "the world the data describes" is what motivated my other reply to you. This distinction gets convoluted when we deal with metadata. Metadata is data whose subject matter is data. So, for example, if we have a table called ALL_TABLES in the SYSTEM schema, and were to abstract an ER model out of such a table, we find that the entity that the data in ALL_TABLES describes is a "table". This is indeed a "database entity".

All of the things you referenced above could be entities. One a casual first glance, I think the data that describes them would all be metadata.

(In Data Architect from Sybase, they made a distinction between "database objects" and "schema objects"). "Object" might be preferable to "entity" here, but "object" conjures up associations that may not be intended.

Most of the time, however, when I've seen the term "database entities" used it's been unfortunate. In some cases, they are conflating the data stored with the world the data is claimed to describe. In other cases, they are analyzing at multiple levels of abstraction without realizing it. Received on Fri Nov 30 2007 - 14:33:55 CET

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