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DAT 601 - Robin Le Couteur - 3/16/2018

Friday, March 16, 2018

ER Modelling Continued pt.1

Today we covered more stuff regarding ER modelling

Firstly, we covered stuff from last lesson as a refresher before we moved on the the next subject

Weak and Strong Entities

Here we looked at different entity types: weak and strong entities. 
Basically, a weak entity is an entity that doesn't have a key attribute by itself, and a strong entity is a normal entity with a key. The weak entity cannot exist without the strong entity it belongs to. 

An example of this is if there was the entities Order and Order Detail. An Order Detail cannot exist unless it exists in an Order because it is partially identified by an order. Basically a recept can have a list of details but you can't have the details without the recept.
Another example is: if there is a car, it can have ownership details, but you can't have ownership details if there is no car to own.

Weak entities can be thought of as complex attributes.



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