Describe informally in what ways the following events di?er from or are similar to transactions with respect to atomicity and durability.

a. A telephone call from a pay phone (Consider line busy, no answer, and wrong number situations. When does this transaction “commit?”)
b. A wedding ceremony (Suppose that the groom refuses to say “I do.” When does this transaction “commit?”)
c. The purchase of a house (Suppose that, after a purchase agreement is signed, the buyer is unable to obtain a mortgage. Suppose that the buyer backs out during the closing. Suppose that two years later the buyer does not make the mortgage payments and the bank forecloses.)
d. A baseball game (Suppose that it rains.)

a. Commit occurs when caller hangs up. Billing information is durable. For line busy or no answer, the transaction aborts. For a wrong number the transaction commits, but later is compensated for by returning the callers money.
b. Commit occurs when license is signed. Marriage is durable (hopefully).
c. Various levels of commit; Every time someone signs something. For example, when purchaser makes an o?er to purchase and includes a deposit, he is committed to either purchase the house at that price (assuming he is approved for the mortgage) or
forfeit the deposit. If he is not approved for the mortgage, he is no longer committed to purchase the house and gets his deposit back. If he does not pay his mortgage payment the transaction is compensated for when the bank forecloses.
d. Commit occurs after game is o?cial. If it rains before the game is o?cial, the game is aborted.

Computer Science & Information Technology

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