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Re: Entity and Relationship - the same thing ?

From: John Eggert <eggertj_at_sympatico.ca>
Date: Sat, 04 May 2002 18:05:30 -0400
Message-ID: <tTYA8.1356$Sc5.366557@news20.bellglobal.com>


Sleeves opined:

> Hello all,
>
> I am studying RDB in a correspondence course, and as such there is no
> tutor
> to confide in. The trouble with it is that you need a degree in the
> english
> language just to understand the way in which the theory is described. For
> instance, having explained entities and it's attributes (example entity
> "customer" with its attributes being "name" "age" etc), we now go onto
> relations and its attributes, where the relation has its primary/foreign
> keys defined using the attributes etc, but am I right in saying they are
> exactly the same thing or am I getting myself totally confused here ?
>
> Many thanks
>
> Alan

Hello Alan:

I too am studying RDB, though I'm self teaching. You are refering to Relations (which is a mathematical term for something that very closely resembles a table), Entities, which are "real world" items (that can be modeled by Relations) and Relationships, which are a means of mapping things that are related in separate tables. (Joins I believe is the correct term) So yes, you do need a strong understanding of language. Even without identical terms haveing very different meanings, the "Relational Model" is based partially on logic. Any understanding of logic requires a very clear understanding of language.

As I said, I am teaching myself this stuff too. I have just finished reviewing my first year algebra to relearn sets etc. and now am slogging through the extremely annoying Introduction to Database Systems by C.J. Date. I recommend this book with a caveat. It relies on what Date calls "Tutorial D". This is a non existant language (non existant in the sense that no computer can run it) that is used for many of the examples. Otherwise, it is quite good.

A final point. When I started learning this stuff, I didn't realize that there are a number of camps in the database world and they fight like cats and dogs. Take all advise given (including this!) with a grain of salt.

Cheers

JE Received on Sat May 04 2002 - 17:05:30 CDT

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