Re: Smart Database Tricks
Date: Fri, 22 Jun 2007 13:03:54 -0700
On Jun 21, 6:32 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
> On 21 jun, 21:17, vldm10 <vld..._at_yahoo.com> wrote:
> > On Jun 18, 7:41 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
> > > So,
> > > since I don't understand your terminology well enough it is simply not
> > > possible for me to continue this discussion in a meaningful way.
> > Before we complete the discussion about the conceptual level I have
> > one question.
> > Here in example1 I gave the identifier of an entity Car. It is about
> > VIN = "vehicle identification number".
> > The identifier is not local for Car entity. It is global. Let me say
> > we have here global lawful information, which is completely accepted
> > as successful solution in the reality and in every country. You state
> > that "...adding such artificial implementation concepts are usually a
> > bad idea..." Can you explain why VIN is a bad idea?
> You misunderstand.
Here I am speaking about identifying. It is identifying the entities
(relationships) and the state of an entity.
They are basic things for DB, not an artificial addition. The entity
is always present in DB. This is identyfying of the entity represented
by its attributes.
I accept entity as it is defined in ER model i.e. that an entity is defined with its attributes. But I gave definition of the state of an entity, which is not defined only by the attributes. Our mind can identify these abstractions separately and keep it as totality.
The identifiers can be applied both, one or neither, depending on purpose, needs, db solution etc.
Of course I am aware that even a variable has its universe and your notice about Universe of Discourse is OK, but it is not essential for identifying entities as abstraction as well as identifying the real objects which we abstract as the entities.
>There is nothing wrong with VIN if it is a natural
> concept that was already present in your Universe of Discourse. What I
> object to is the artificial addition of such concepts if they are not
> already present. The problem with your definitions is that they are
> not precise enough to say whether they are or not.
> > > If this is a relation then
> > > all columns are attributes and since you have represented all the
> > Can you please, tell me what is the definition of the attribute in RM.
> The column of a relation. Conceptually it models a role in the
> predicate that is associated with the relation.
> -- Jan Hidders- Hide quoted text -
> - Show quoted text -
Vladimir Odrljin Received on Fri Jun 22 2007 - 22:03:54 CEST