代写 COMPSCI/SOFTENG 351 and COMPSCI 751

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代写 COMPSCI/SOFTENG 351 and COMPSCI 751


Assignment

COMPSCI/SOFTENG 351 and COMPSCI 751

due Thursday 31 March 2016, 5pm

The assignment is marked out of 20. For COMPSCI/SOFTENG 351 students, it is worth

10% towards your final mark. For COMPSCI 751 students, it is worth 8% towards your final

mark.

Exercise1. The following relational database schema Auction models the business

data of an online auction system:

– Person={pid, pname, phone, location} with key {pid},

– Item={iid, iname, description, sid} with key {iid}, and foreign key [sid] ⊆ Person[pid]

– Bid={bid, iid, price} with key {bid,iid,price}, and foreign keys

[bid] ⊆ Person[pid]

[iid] ⊆ Item[iid]

– Sale={iid, bid, price} with key {iid}, and foreign keys

[iid] ⊆ Item[iid]

[bid] ⊆ Person[pid]

[iid, bid, price] ⊆ Bid[iid, bid, price]

A double-bidding occurs whenever two different bidders bid for the same item at the

same price. For each of the 5 queries in a) to e) do the following:

– Write the query in Domain Relational Calculus.

– Without using either inequalities or conjunctions or disjunctions in conditions of

the selection operators, write the query in Relational Algebra

a. List the names of items that had bids of $50 that did not sell.

(4 marks)

b. List the names of all the items that have been affected by double-bidding. (4 marks)

c. List the names of all the items that have never been affected by double-bidding.

(4 marks)

d. List the names and phone numbers of the bidders who are not always affected by

double-bidding. (4 marks)

e. List the names of bidders who have bid on every item that has sold. (4 marks)

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代写 COMPSCI/SOFTENG 351 and COMPSCI 751