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

Exercise No. 56: An Accident (dfm)

In this simplified E/R schema a driver causes an accident - which can be categorised by type - in a certain area. This area belongs to a city district and the district is part of a city. Sometimes an emergency vehicle which can also be categorised by type is needed. The accident can be watched by a witness.. The time dimension consists of day and week.

Figure D.E.45.1 - an accident

Please identify the fact of interest and build the attribute tree. We only need a classification by district and city, neglecting the area of an accident. Some attributes 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.

There is only one fact attribute "fault" which is a binary variable (parameter value 0 or 1, depending on whether the accident was the driver's fault or not) that may be aggregated using the "average" operator along all dimensions.

Solution

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

Exercises List