Suppose that a large store has a transactional database that is distributed among four locations. Transactions in each component database have the same format, namely Tj: {i₁,..., im}, where T; is a transaction identifier, and ik (1 ≤ k ≤ m) is the identifier of an item purchased in the transaction. Propose an efficient algorithm to mine global association rules. You may present your algorithm in the form of an outline. Your algorithm should not require shipping all of the data to one site and should not cause excessive network communication overhead.

Consider a database table that includes a salary attribute. Suppose the three queries avg, count, and max (in that order) are made on the salary attribute, all conditioned on the same predicate involving other attributes. That is, a specific subset of records is selected and the three queries are performed on that subset. Suppose that the first two queries are answered and the third query is denied. Is any information leaked?

Two students are enrolling in the same course, but there is only one open seat. Is it feasible to allocate both students the last vacant seat in a database system?

Consider the relation prereg in the University Database and its transitive closure defined in Section 5.4 of the textbook. Consider the recursive query in Figure 5.16 that outputs this transitive closure. Write a recursive query that finds all direct or indirect prerequisite of BIO-301. Output a table with one column that contains the IDs of all such prerequisites. Note that your query must work correctly not only for the given instance of prereg, but also for all possible instances. Run this query.