Re: Entity and Relationship - the same thing ?
Date: 5 May 2002 08:50:56 -0700
>> 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 - 17:50:56 CEST