Analysis on three paradigms of Database Design

  

 

• Superkey: the attribute set that uniquely identifies a tuples in a link is called the superkey of The Link mode.
• Candidate Key: No superkeys with redundant attributes
• Primary Key: The candidate key selected by the user as the record ID

From this we can see that the combination of superkeys is unique, but it cannot be the smallest and unique.

Answer:Student ID, which is unique and has no redundant attributes; name, which is unique and has no redundant attributes.

What is data dependency? Data Dependency refers to the dependency between a relational mode. The most typical example is function dependency.

2. Local dependency and full dependency:

In the figure: If W-> A exists in X and W, X-> A is true, W-> A is A local dependency, otherwise, W-> A is completely dependent.

X-> Y, Y-> A, and Y/>X and A do not belong to Y, So X->Yes..

 

Second paradigm: mainly to eliminate local Dependencies

Third paradigm: eliminate transmission Dependencies

R (course No., instructor No., instructor title) in the relationship model, if the course No.-> instructor No., instructor No.-> instructor title, the course number> instructor title is a transfer dependency. So it is not the third paradigm. In this case, R will be redundant and abnormal. For example, if a teacher opens five courses, there will be five records in the relationship, and the instructor title will be repeated five times.