Answer just one of the following questions. Be sure to read other student posts

Question

Answer just one of the following questions. Be sure to read other student posts and work to not duplicate information that has already been provided. 1) What is Dr. Codd's relational model and what does it include 2) Contrast the terms relation, tuple, and attribute with table, row, and column. 3) Describe the relationship between a superkey, a candidate key, and a primary key. Give an example. 4) Explain where you can use business rules in an organization. 5) Describe and give an example of one of the following: - derived attribute - multivalued attribute - ternary relationship - required attribute

Explanation / Answer

3) Describe the relationship between a superkey, a candidate key, and a primary key

Super key: Its basically the attribute or set of attributes that uniquely identify a tuple into the relation. Suppose we have a table name student(student_id, student_name, student_address, phone_no)

Here student_id is super key.

Here combination of attribute student_name and student_address is also a super key.

Candidate Key: Candidate key is a super key for which no proper subset is a super key. Here in the above example student_id is also a candiate key.

Primary Key: Primary key is a candidate key, chosen by database deginer for unique mean of identifying a tuple into a realtion. Primary key is always unique and not null

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