Let R = (A, B, C), and let r1 and r2 both be relations on schema R. Give an expression in the domain relational calculus that is equivalent to each of the following

Let R = (A, B, C), and let r1 and r2 both be relations on schema R. Give an expression in the domain relational calculus that is equivalent to each of the following:

1. (r1)
2. =17 (r1)
3. r1 ∪ r2
4. r1 ∩ r2
5. r1 − r2
6. (r1) (r2)

Let the following relation schemas be given:

R = (A, B,C)

S = (D, E, F)

Let relations r(R) and s(S) be given. Give an expression in the tuple relational calculus that is equivalent to each of the following:

1. (r )
2. =17 (r )
3. r × s
4. ( (r × s))

Keeping organizational information in a file system has a number of major disadvantages. Cite 4 of these disadvantages.

1. Consider the following relation:

Article (ID, Title, Journal, Issue, Year, StartPage, EndPage, TeachnicalReportID)

It contains information of articles published in scientific journals. Each article has a unique ID, a title, and information on where to find it (name of journal, issue, and which pages). Also, if the results of an article previously appeared in a technical report, the ID of this technical report can be specified.

The following is an instance of the relation:

Based on the above, indicate for each of the following sets of the attributes whether it is a key (candidate key) for Article or not and write a brief explanation for each answer:

1. {ID}

2. {ID, TechnicalReportID}

3. {ID, Title, TechnicalReportID}