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Exercises for the Course Datawarehousing, SS 2002, Prof. R. Bayer, TUM Exercise Sheet 2

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Exercises for the Course Datawarehousing, SS 2002, Prof. R. Bayer, TUM

Exercise Sheet 2

Exercise 4, Ch.2-5: Schema optimization

Consider the data warehouse schema of Exercise 1. Reduce the dimensionality of the fact table by exploiting the fact that the location of a mobile phone user usually can only be determined by the current cell. Make sure that the location information of the cell (specified by the location of the cell tower) is not lost.

a) Define the new schema

b) How many dimension tables are now required?

c) What is the size of the new universe, assuming around 20.000 cells in Germany?

Exercise 5, Ch.2-5: Schema optimization

Are there further possibilities to reduce the dimensionality or the size of the fact table without losing information?

If yes, present the new schema and calculate the new size of the universe and the fact table with data of one year. What is the disadvantage (if there is any) of this optimization?

Exercise 6, Ch.2-5: Schema extension

Extend the schema of Exercise 5 to support following location-based analysis: “Average percentage of calls within the city (or region, state) where the customer is living”. Provide an extended star-schema as well as a snow-flake schema. Give a rough estimate of how much space can be saved with the snow-flake schema.

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