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)
    1

    代写 COMPSCI/SOFTENG 351 and COMPSCI 751