CS145 Midterm sample

CS145 Midterm sample - CS145 Midterm Examination Autumn...

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CS145 Midterm Examination Autumn 2006, Prof. Widom Please read all instructions (including these) carefully. There are 6 problems on the exam, with a varying number of points for each problem and subproblem for a total of 75 points to be completed in 75 minutes. You should look through the entire exam before getting started, in order to plan your strategy. The exam is closed book and closed notes, but you may refer to your three pages of prepared notes. Please write your solutions in the spaces provided on the exam. Make sure your solutions are neat and clearly marked. You may use the blank areas and backs of the exam pages for scratch work. Please do not use any additional scratch paper. Simplicity and clarity of solutions will count. You may get as few as 0 points for a problem if your solution is far more complicated than necessary, or if we cannot understand your solution. Throughout the exam you should assume and use “pure” SQL, XPath, and XQuery as cov- ered in class—not dialects of these languages supported by a particular implementation (such as Oracle, mySQL, or Saxon). NAME: In accordance with both the letter and spirit of the Honor Code, I have neither given nor received assistance on this examination. SIGNATURE: Problem 1 2 3 4 5 6 TOTAL Max. points 15 10 12 16 16 6 75 Points 1
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1. Functional Dependencies, Normal Forms, and SQL (15 points) Consider the following table storing temperature readings taken by sensors: Temps(sensorID,time,temp) For example, a tuple (s26,13:42,76) in Temps says that at time 13:42, sensor s26 reported a temperature of 76 degrees. (Don’t worry about dates—perhaps our sensors are active for only one day.) Assume for all parts (a)–(e) of this problem that the pair of attributes [sensorID,time] is a key for table Temps , and Temps has no other key. (a) (2 points) Suppose the following functional dependency holds on table Temps : time temp State in English what real-world property is captured by this FD. (A real-world prop- erty is described by a phrase or sentence discussing sensors, times, and/or temperatures, while not mentioning tables, tuples, and/or attributes.) Please be brief—a short phrase or one-sentence answer is sufficient. (b) (2 points) Continuing to assume that FD
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CS145 Midterm sample - CS145 Midterm Examination Autumn...

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