-- Oct 16 In-Class Exercise Thread

If we have two relation entities, named college and university, and considering different colleges come under a university, there we can have partial keys for both college and university which can make a primary key. For example, partial key for university and college would be “university address” and “college name”. Therefore, college name would be a weak entity set since without university, college will not exist

-- Oct 16 In-Class Exercise Thread

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-- Oct 16 In-Class Exercise Thread

1) Stores sell certain products. Customers cannot purchase the product without knowing which store the product is sold at. 2) A transcript needs the student name and classes with grades and units.

-- Oct 16 In-Class Exercise Thread

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-- Oct 16 In-Class Exercise Thread

Example 1) A cubicle number belongs in an office building. You can't have a cubicle be alone outside an office building. Theoretically yes you could have a standalone cubicle outside in the open but that's more of a random desk outside. Example 2) Another example would be in an enterprise HR BU, storing employee name and contact info, while in another instance storing employee salary. Salary is only relevant to an employee.

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1. You might have Musicians and Songs. Songs have an attribute "title". A Song is "Written by" a Musician. Since there might be multiple songs with the same name, you would need to know which musician you're talking about. 2. A song might be owned by a record label, written by a composer, and sung by a vocalist. If we were to break this apart into separate two-way relationships, we might depend on the keys of Composers, Vocalists, and Labels.

-- Oct 16 In-Class Exercise Thread

1. A relation between mammals like birds and their sub-species 2. A weak entity for image objects depending on the main object name. It coul be a picture of different object like tree, bottle, ball, etc

-- Oct 16 In-Class Exercise Thread

Ex 1) [[https://postimg.cc/jwKcgwYP]] Dependent is a weak entity because it relies on the Professor. Ex2) BankAccount(bankerId, bankerName, bankerEmail) If a particular bank does not exist, the bank account for that bank would cease to exist even with banker ID, name and email.