Hierarchies in dimensional modeling

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Hierarchies in dimensional modeling

Post  exhortae on Sun Aug 01, 2010 5:13 pm

Hi,



I have a little problem modeling hierarchies for a data mart.

Lets say I'm building a datamart for students grades in a university. In this university you have units of teaching and each unit of teaching (UT) is composed of one to many courses (Course). The fact table is composed of student's grades in courses.

What is the difference between those two ?
- Make two dimension 1 is dim_unit_of_teaching et 2 is dim_course.
- Make a flat dimension with a column unit_of_teaching and a column course


I guess if I go with making two dimensions I'm loosing the hierarchy, am I right ?

Thank you


PS : excuse me for my english.

exhortae

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Re: Hierarchies in dimensional modeling

Post  ngalemmo on Mon Aug 02, 2010 11:53 am

If a course can only belong to one unit of teaching (I'm assuming you mean Department or College), then the flat option, storing unit of teaching as an attribute of the course is the simplest solution. But, doing so does not mean you would not have a unit of teaching dimension for other purposes.

If, on the other hand, your are classifying courses based on requirements for a Degree, then it is essentially the same thing as a Bill of Materials and needs to be handled by a hierarchy bridge.
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Re: Hierarchies in dimensional modeling

Post  exhortae on Wed Aug 04, 2010 12:04 pm

Hi,

In a french university system, the year is divised in two semesters, in each semester you have several units of teaching (several courses are grouped in a unit of teaching).

Like MAX45 would be a unit of teaching named Mathematics which is composed of 3 courses
-Geometry
-Arithmetic Analysis
-Probabilities


By hierarchy bridge you mean some kind of recursive relationahsip like in a parent child relation? if it's yes it's not the case here.

Thanks

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