Studierende stehen vor dem LC und blicken lächelnd einer Kollegin mit einer Mappe in der Hand nach.

Exercise No. 47: Lecture at the UCLA (apa)

The following cube stores data about lectures at the UCLA.

Lectures at the University of California - Los Angeles are hold by a lecturer who is of a certain type. Students who can also be classified according to their type attend a lecture. A lecture has a certain subject which belongs to a certain subject group and takes place in a certain lecture hall. This hall is part of a university building. The time dimension consists of day and week.

We have five dimensions with the following hierarchical structure:

Table A.E.31.1 - lectures at the UCLA

Please build the Aggregation Path Array and assume the following end-user requirements:

1) "a roll up by the time dimension starting at weeks for each lecturer independent of all other dimensions"

2) "a daily report for each lecture hall independent of all other dimensions"

3) "a complete drill-down by the time dimension down to day for each combination of student and subject, irrespective of all other dimensions"

Select the corresponding cells in the APA and choose the cubes to materialize, then highlight the derivatives of those cubes.

Solution

Figure A.E.31.1 - The resulting APA with the redundancy free-set highlighted

Size of the redundancy-free set (including the base cube): 243

Required cubes, the materialization decision and derivatives

The blue area represents the end-user requirement 1 ("a roll up by the time dimension starting at weeks for each lecturer independent of all other dimensions"), requirement 2 ("a daily report for each lecture hall independent of all other dimensions") and requirement 3 ("a complete drill-down by the time dimension down to day for each combination of student and subject, irrespective of all other dimensions").

Materializing cube v = (ST_*,SU_*,LH_*,LE_le,T_w) (dark blue cell "T_w", representing end-user requirement 1), cube w = (ST_*,SU_*,LH_lh,LE_*,T_d) (dark green cell "LE_*", representing end-user requirement 2) and cube x = (ST_st,SU_su,LH_*,LE_*,T_d) (red cell "LE_*", representing end-user requirement 3) offer us the following sets of derivatives.

Figure A.E.31.2 - Derivatives of cube v = (ST_*,SU_*,LH_*,LE_le,T_w)

Figure A.E.31.3 - Derivatives of cube w = (ST_*,SU_*,LH_lh,LE_*,T_d)

Figure A.E.31.4 - Derivatives of cube x = (ST_st,SU_su,LH_*,LE_*,T_d)

Figures A.E.31.2 to A.E.31.4 show that no end-user requirement is covered by the derivatives of another vector. To meet all end-user requirements we will have to materialize all three cubes, v, w and x.

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