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

Exercise No. 14: Bus Maintenance (log)

We will now build a logical model for the "bus maintenance" case.

We have four dimensions with the following hierarchical structure:

Table L.E.28.1 - bus maintenance

"Costs" and "no. of services" are the key figures in this example. Each bus has an additional attribute "B_bu_age", the age of the bus and each driver has an additional attribute "D_dr_exp", the driver's experience.

Please draw the Classic Star and the Fact Constellation Schema. Then draw the example's dimension tables normalized and use them to build a Snowflake Schema!

Solution

This case's Classic Star Schema has five tables, a central fact table and four dimension tables. The latter consist of a generated key as well as a key and a text field for each hierarchy (except the total aggregation) and the level attribute. The fact table uses the generated keys from the dimension tables as a combined key and contains two key figures ("costs" and "no. of services") in this example:

Figure L.E.29.1 - The Classic Star Schema

The Fact Constellation Schema for this case consists of four dimension tables and 12 fact tables (2x1x2x3):

Figure L.E.29.2 - The Fact Constellation Schema

Normalizing the dimension tables completely means that only the key of the next higher level is kept in each table. Please note that the tables for the total aggregation level have been neglected in Figure L.E.29.3

Figure L.E.29.3 - DT normalized

The Snowflake Schema is a combination of the Fact Constellation Schema's fact tables and the dimension tables either partitioned or normalized (normalized in this case):

Figure L.E.29.4 - The Snowflake Schema

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

Exercises List