Re: Objects and Relations

On Feb 21, 12:03 am, "Walt" <wami..._at_verizon.net> wrote:
>
> In casual conversation, ER modelers will tend to use the simple word
> "entity" in place of either "entity set" or "entity instance", leaving the
> listener to disambiguate by means of the context in whuch the word appears.
>
> By analogy, in casual conversation, object oriented programmers will use the
> simple word "object" in place of either "object class" or "object instance",
> similarly leaving disambiguation up to the listener.
>
> The problem comes when the listener is not familiar with the underlying mode
> of thinking. In that case, the listener will sometimes disambiguate
> incorrectly. That is why introductory tutorials on object oriented
> programming tend to spell out "object class" or "object instance", at least
> until the reader can be presumed to have gotten accustomed to the mode of
> thinking. I'm sure you will have noticed this, if you've gone back and read
> some introductory material after gaining proficiency.
>
> Similarly, introductory material on ER modeling should spell out when we
> are talking about the "set of all vehicles" and when we are talking about "a
> particular vehicle". Some such material does this.
>
> Discourse in this newgroup tends to be a little more formal than casual
> conversation, but far less formal than introductory tutorials.
>
> Hope this helps.

I prefer to only use "object" to mean instance. Why would one say object when one means class? ie given that we have different words for these different concepts, let's use them!

A word like "book" can mean an instance as well as a type, depending on the context. It could be argued that it really means a type, and its use for naming an instance is a curious feature of how we communicate because we don't generally want to go to the trouble to give things around us explicit names.

I agree that "entity" can have both meanings as well. However, I was taking the statement "entities are illusionary" to mean that all instances of entities are illusionary, rather than only entity types.

It is interesting that in UML we have class diagrams and object diagrams. An ERD is analogous to a class diagram. That could explain Jim's tendency to regard "entity" as being a type. Received on Wed Feb 21 2007 - 03:06:35 CET