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Exercise No. 32: Haircut (dfm)

This simplified E/R schema shows an information system of a hair dressing salon.

A customer will get a haircut by a stylist who works for a branch office and who has a certain experience (junior stylist, master stylist, etc.). The salary, the price of a haircut etc depends on the experience and therefore experience is added as an entity. The stylist may be assisted by an apprentice.
The time dimension consists of day, week and month.

Figure D.E.69.1 - haircut

Please identify the fact of interest and build the attribute tree.
Attributes that cannot be used for aggregation in a meaningful way 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.

Solution

Entity HAIRCUT 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.69.2 - The attribute tree

Customer, stylist and apprentice are defined as dimensions and the dimension day is introduced as a range of the date attribute. The dimension apprentice is tagged as optional. The attribute costs becomes the only fact attribute.

The dob of the patient customer and the address of the branch connot be used for aggregation and are tagged as non-dimension attributes.

Figure D.E.69.3 - The fact schema

price = SUM (HAIRCUT.price)

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

Exercises List