Homework 4 for CSC691D: Advanced Database Management

You are allowed to collaborate for this homework. Form teams of 1-3 students. Mention the names of your partners on your homework.

Examples

Conference example

Consider, as an example, person X who is traveling from New York to Los Angles to attend a conference from June 11, 1997 to June 14, 1997. X wants to leave New York on June 11 and leave Los Angles on June 14 and X must stay at hotel Equator, the site of the conference. X prefers to fly on Delta, United or American in that order. X will not travel on any other airline. The car must be rented from Avis or National with which X's company has corporate accounts.

The workflow activity involves making flight and hotel reservations, and optionally a care rental reservation. If no flight or hotel is available, the whole trip is cancelled. If a care cannot be rented, the trip can still proceed since X can take public transportation

House Example

Jeff wants to buy Mr. Spaceley's house. However, neither of the two parties trusts each other. Jeff needs to give money to Mr. Spaceley in order to get the house title from him. Jeff, however, refuses to give money to Mr. Spaceley first. He says that Mr. Spaceley should believe him and give him the title first. After long discussion both Jeff and Mr. Spaceley put up an escrow.

Problems

(20 points each) Identify various spheres of control, explain control and data flow, and draw a diagram that contains identified spheres for the examples given above.
(15 points each) Explain how the workflows of the above problem will be executed.
(10 points) Consider atomic dataset 1 ADS1 and ADS2. Also, assume that t1 and t2 are in ADS1 and that t3 and t4 are in ADS2. Assume that ADS1 and ADS2 are in the same global database G. Give an example of a history that is not serializable in G but is predicate-wise serializable in ADS1 and ADS2.
sample answer: t1->t2, t2->t4, t4->t1, t3->t4
These transactions are conflict serializable within the context of their respective atomic data sets but are not when the entire database is considered since t1->t1.
(10 points) Consider two database sites S1 and S2. Assume that t1,t2, and t3 are at S1 while t4 and t5 are at S2. Assume that t6 accesses objects at S1 and S2. Give an example of a history that is not serializable but is quasi-serializable. See section 4.1.4 on Quasi Serializability in Ramamritham.
sample answer: t1->t2, t4->t5, t6->t3, t3->t1
Quasi-serializability does not restrict indirect interaction between global and local transactions. consequently the t1->t1 violates serializability but not quasi-serializability.

Postscript version of HW#4

Homework set by:

singh@ncsu.edu