What is the difference between controlled and uncontrolled redundancy? Illustrate

What is the difference between controlled and uncontrolled redundancy? Illustrate with examples.

What are the main reasons for and potential advantages of distributed ­databases?

Describe the two alternatives for specifying structural constraints on relationship types. What are the advantages and disadvantages of each?

Can an identifying relationship of a weak entity type be of a degree greater than two? Give examples to illustrate your answer.

 4.1. What is a subclass? When is a subclass needed in data modeling?

4.7. What is the difference between a specialization hierarchy and a specialization lattice?