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DAT 601 - Robin Le Couteur - 3/13/2018

Tuesday, March 13, 2018

ER Diagrams


In todays class, we covered a number of different points regarding ERD's. Some of the stuff I remember from DAT 5, but there was some new stuff that I didn't know.

We covered concepts like what an entity is vs an entity type or entity set.

Some info I already knew that we covered included attribute types, so it was good just as a refresher. The concept of derived attributes and stored attributes was new though but easy to understand. 

The subject of keys was quite interesting though because I had only dealt with composite, foreign, primary, and candidate keys. I now know that foreign keys should be ignored in the conceptual ERD, and I understand superkeys. Superkeys are used to uniquely identify a tuple(which is basically a row in a database).

 Lastly, we covered relationships and how you can have binary, ternary, and more relationships between different entity types. You can also have one entity type in a relationship which is called a unary relationship. An example of a unary relationship is where an employee might supervise another employee, so there is only one entity type in a recursive relationship. We also quickly covered basic cardinality which I already know(One to one, one to many, many to many)


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