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

Exercise No. 1: Flying Airplane (dfm)

This simplified E/R schema shows a captain flying an airplane.

Each airplane belongs to a certain airplane type and to a certain airline (parallel hierarchy). The time dimension consists of day, week and quarter.
 

Figure D.E.1.1 - a captain flying an airplane


Please identify the fact of interest and build the attribute tree. No attributes have to be pruned or grafted, but some of them cannot be used for aggregation in a meaningful way. Those should be tagged as non-dimension attributes in the fact schema.

Then derive the fact schema from the tree by defining dimensions, fact attributes and hierarchies and build a glossary for the fact attributes if there are any.

Please include an additional fact attribute counting the number of flights.

Solution

Entity FLIES is chosen as the only fact. Its identifier becomes the root of the attribute tree. All other attributes or identifiers become nodes.

Figure D.E.1.2 - The attribute tree


Captain and airplane are defined as dimensions, dimension day is introduced as a range of the date attribute. No. of flights is added as the only fact attribute.

The date of birth of a captain and the age of a airplane cannot be used for aggregation and are tagged as non-dimension attributes.

Figure D.E.1.3 - The fact schema

no. of flights = COUNT(FLIES)

This exercise is part of a case study: dfm - apa - log

Exercises List