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