Hi, I would like to know if the case study does not mention about a unique identifier for an entity (e.g. Vehicle Make / Nominated driver), are we allowed to make a unique identifier ourselves (e.g. Nominated Driver ID, etc.)? Thank you.

Hi Jieh Chia, When identifying primary keys, you may encounter a situation where there are no natural primary keys, or the ones available aren't suitable, so you can essentially make a surrogate key (which is what you're suggesting). A surrogate key is a primary key created by the database designer to simplify the identification of entity instances. Surrogate keys are useful in the following situations: When there is no natural key. When the selected candidate key has embedded semantic contents (or is unusable due to privacy concerns). When the selected candidate key is too long. I hope this helps. Thanks, Adam. "Jieh Chia" <24*1*5*4@s*u*e*t*u*a*e*u*a*> wrote:

Hi, let's say for a certain entity the primary key could be a combination of some attributes which includes a foreign key. In ERD we are not supposed to note down foreign keys so in this case should I create a surrogate key?

Well if the combination of attributes makes up the primary key, then it would be a composite primary key so you would show it as the key. It just also gets partially used by another table as the foreign key so it would just not be labelled as the foreign key, I wouldn't remove it as such. I found this while searching if it helps: key - a minimal set of attributes that uniquely identifies a record (or row) primary key - a single attribute that (a) cannot be null, and (b) uniquely identifies a row. composite key - two or more attributes that, taken together, uniquely identifies a record (or row) foreign key - an attribute in a table that references the primary key in another table. Can be part of a composite key. (Could also be a primary key, though this would mean the 2 entities/tables should be logically combined.) https://opentextbc.ca/dbdesign01/chapter/chapter-8-entity-relationship-model/