- Consider an un-normalised relation ‘library book loan’ which includes information about books which have been borrowed, i.e. book identifier, title, author, borrower number, borrower name, date-out and date-due.
Which problem is associated with the term ‘redundancy’?- We cannot record a new borrower in our table unless there exists a loan for that borrower
- We could change the borrower name in one tuple, while leaving it fixed in another.
- If a borrower has only borrowed one book and we remove that tuple, we might lose all the information about the borrower.
- The borrower name is repeated for each borrower in the relation.
- Given the following determinacy diagram:
Which one of the following sentences could be used to describe the diagram?- Student no. determines Student name
- Student name determines Student no.
- Student no. is functionally dependent on Student name
- Which of the following statements describes the term ‘functional dependency’:
- Given a relation which has attributes (x, y, …), we say that an attribute y is functionally dependent on another attribute x, if (and only if) each y value has associated with it precisely one x value (at any one time).
- In a relation, if attribute y is functionally dependent on attribute x, then every one of the tuples in the relation where the x-value appears must contain the same y-value.
- Assuming a relation with attributes a, b and c which are each functionally dependent on attribute x - given a particular x value, there exists at least one corresponding value for each of the a, b and c values
- The normalisation process at 2NF always involves two of the following – which one does it not involve?
- A composite key
- Transitive dependencies
- Partial dependences
- Which one of the following describes a transitive dependency?
- If x determines y and y determines z then x must determine z
- If x determines y and x determines z then y must determine z
- Neither of the above
- Both of the above
- A partial dependency cannot exist if a relation is in:
- Un-normalised form
- 1NF
- 2NF
- A transitive dependency cannot exist if a relation is in:
- Un-normalised form
- 1NF
- 2NF
- 3NF
- In 3NF, by removing attributes not directly dependent on the primary key we further reduce redundancy. True or False?
- True
- False
- The BCNF rule states that all the determinants must be ___________ keys. The missing word is:
- candidate
- primary
- foreign
- A relation is in 4NF if there are no multi-valued dependencies between the attributes – i.e. it forbids independent many-to-many relationships between attributes.
True or false?- True
- false