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

Exercise No. 13: Writing Tests (dfm)

This E/R-schema is about students (who are of a certain type) writing tests. The test is supervised by an assistant and rated by a professor.The time dimension consists of semster and year.

Figure D.E.25.1 - writing tests

Please identify the fact of interest and build the attribute tree. No attributes have to be pruned or grafted.

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

Solution

Entity TEST 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.25.2 - The attribute tree

Professor, student and assistant are defined as dimensions, dimension semester is introduced as a range of the date attribute.

The attributemark is selected as a fact attribute which is non-additive along all dimensions (it may be aggregated using the "average" operator along all dimensions).

Figure D.E.25.3 - The fact schema

mark = AVG(TEST.mark)

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

Exercises List