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Exercise No. 34: Writing Articles (dfm)

This simplified E/R schema shows an author writing an article for a newspaper..

An author writes an article for a certain newspaper. The article belongs to a certain subject group, the newspaper is of a certain type. Before the artcile is published in the newspaper it is controlled by a lector. The time dimension consists of month and year.

Figure D.E.7.1 - Author writes an article

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 writings.

Solution

Entity WRITES 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.7.2 - The attribute tree

Author, article, newspaper and lector are defined as dimensions, dimension month is introduced as a range of the date attribute. No. of writings is added as the only fact attribute.

The date of birth of a lector, the title of an article and the address of an author cannot be used for aggregation and are tagged as non-dimension attributes.

Figure D.E.7.3 - The fact schema

no. of writings = COUNT(WRITES)

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

Exercises List