CS 511 Design of Database Management System
Homework 1
Due: 2:00 PM CST on September 12, 2007
NOTE: Please submit a hard copy of your homework. Bring it to the lecture table at the
beginning of the lecture on 12th September, 2007. The hard copy should be as clearly
readable as possible. You may be subtracted points for unreadability and ugly
presentation.
I2CS Students: You should email your solutions to the TA([email protected]) in the
pdf or the word format. Please send your email with subject “CS511-HW1” and solution
file attached by 2PM UIUC time (CST).
Problem 1: Relational Model [20 Pts]
Briefly mention two flaws of the relational data model.
Problem 2: Relational Model [30 Pts]
Scientists use multiple sensors to gather temperature information of a specific object in
scientific observations in order to obtain exact result. Each sensor observes temperature
information every second, and sends the data to the main server to be stored on specific
times. A sensor would sometime report nothing (null value) or wrong value due to the
physical problems. Scientists have to use data from all sensors to find out the most
precise temperature at each time. Hence, they merge and take average of the observed
data for each observation. They also compute differences among data gathered in
different times, or compound them to see temperature behavior during longer time period.
One dimensional array is a good fit to represent this data. Specify and formulate an exact
data model to represent the data and an algebra that covers the required operations. You
could add additional data item(s) to the array structure in your model.
Problem 3: System R [30 Pts]
[30 Points] In relational database management systems like system R when user does not
assign any value to a column in a row, it is tagged by especial value called null.
1- Give two different interpretations of having a null value in a column of type
Boolean.
