DavidSzczesniak
1/17/2018 - 11:42 AM

ERD Entities

This refers to a definable thing like a person or object - that can have data stored about it. They can be thought of as nouns (e.g. a customer, student or car)

\!h Entity type 
A group of definable things, like students or athletes.

\!h Entity set 
Same as type, but defined at a particular point in time. Similar to instance, where the person or car would be an instance of the entity set.
For example, 
- Students enrolled in a class ->on the first day<-
- Customers who purchased ->last month<-
- Cars ->currently<- registered in Florida

\!h Entity categories 
Strong entities - These can be defined solely by their own attributes, weak entities cannot.

\!h Associative entities
- They associate entities within an entity set.
- A way to simplify many-to-many relationships.
- Done by connecting to the original entities through a many-to-one and a one-to-many relationship.