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Re: table : row : column = entity : occurrence : ?

From: Jan Hidders <hidders_at_REMOVE.THIS.win.tue.nl>
Date: 17 Dec 2000 21:49:28 GMT
Message-ID: <91jcd8$cs7$1@news.tue.nl>

TC wrote:
> I have a question about the terminology used in database design.
>
> Suppose I have a table that stores flower data. One of the records
> represents the lily and one of the fields holds habitat info. If I am not
> mistaken, "flower" is an entity and "lily" is an occurrence of that entity,

Although many books use this (sloppy IMHO) terminology, I think it is better to describe "flower" as en entity *type* and 'lily' as entities that are occurrences (or instances) of that type.

Note, by the way, that this terminology belongs to the world of Entity-Relationship modelling. If you are talking about tables then you are talking about the relational model, which is very much connected to it, but certainly not the same. For instance, not every tuple in a relation represents neccessarily an entity.

> where "entity" and "occurrence" are specific technical terms in the database
> world. What, then, is "habitat"? I can think of several words that might
> apply ("property", "attribute", etc.), but if there is an established term I
> would like to know it.

In ER modelling it is usually called an attribute, but sometimes also a property.

> Can anyone recommend a book that discusses database design theory at this
> level?

"An Introduction to Database Systems" by C.J. Date

-- 
  Jan Hidders
Received on Sun Dec 17 2000 - 15:49:28 CST

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