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Re: Entity and Relationship - the same thing ?

From: --CELKO-- <71062.1056_at_compuserve.com>
Date: 5 May 2002 08:50:56 -0700
Message-ID: <c0d87ec0.0205050750.34b38ba3@posting.google.com>


>> 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 ? <<

Not quite the same thing, even if you are using tables to represent both. An entity can exist by itself, but a relationship needs entities to exist. For example, I can be a single person by myself, but I need a wife to be in a marriage. My marriage can have some properties which belong to it alone (license number, date, jurisdiction, fees). If one of us (or both) dies, then there is no longer a marriage.

I can have some other complex rules about the relationship and its entities; marriages are a good example: how many wives?; how many husbands?; can you marry your cousin? your sister? your mother?; can I remarry? etc.

Any help? Received on Sun May 05 2002 - 10:50:56 CDT

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