Comp150CPA: Clouds and Power-Aware Computing
Midterm Examination.
April 6, 2011 -- Open Notes

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Please answer the following questions on these sheets. Please put your name at the top of each sheet. You may use any printed material. Electronic devices are prohibited.

1. (20 points) Can an object marked as @Persistent in AppEngine contain an instance of another @Persistent object as a member? Why or why not?
2. (30 points) Suppose you have an input that has entries like the following:

    
   time person activity 
   

   where
   • time is a timestamp of the event in seconds since Jan 1, 1970 00:00:00 GMT.
   • person is the name of a person.
   • activity is the name of the activity that was started at this time, e.g., "sleeping", "running", "walking", "working", etc.
   Please write a Pig script that computes the total time that George spent sleeping. This is the sum of the differences between times that George started sleeping and times that George started doing something else. For example, for the data

    
   10001  George sleeping
   10006  George walking
   10100  George sleeping
   10200  George showering
   10500  George running
   

   your program should output the number 105, which is 10006 - 10001 + 10200 - 10100. You may assume that every time George starts sleeping, there is another subsequent event when George stops sleeping.
   

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3. (25 points) List the disadvantages of structuring a program via service-oriented architecture (SOA). Then explain why these disadvantages are less important than the business needs that are satisfied through SOA.
4. (25 points) You are designing a stock-market analysis tool that takes as input events of the form:

   time stock change
   

   where:
   • time is a time of day.
   • stock is a stock code.
   • change is the change in value (in + or - points).
   You wish to analyze these in a variety of ways, looking for subtle correlations.
   1. (10 points) Should you use a datastore with strong or eventual consistency? Why?
   2. (15 points) Should you use a Map/Reduce or Distributed-Hash-Table infrastructure to store the data? Why?