Does this database model make sense?

Question

I am new speaking about modelling databases. But I give my best to learn as much as possible by my own. Therefore I want to ask you, whether my first attemp make sense for the following example:

So I modeled the database as followed:

The databse is about medicine. There are several medicine items which should be dosed depending on the age of the patient. Every medicine item can belong to one ore more groups (or none).

This is just a test case to show what I learned so far. So every tip to improve my skills is welcome!

Thanks a lot!

Answer 1

1. The relationtable table name is just a placeholder, right? It should be more descriptive, maybe dosage ?

2. Something tells me that age ranges will greatly vary. Some medicines have different rules for children under 3 years, other under 5, 10, and so on. Instead of creating a separate table, just include two extra columns ( start and end ) in relationtable . It will be much easier to query and I won't consider this a denormalization.

3. Talking about age and dose tables - get rid of unit column and use normalized, fixed unit. Years for age and mg for doses. This will make querying much simpler. Don't be afraid to use floating numbers, eg 0.5 to represent six months.

Answer 2

I agree with what Tomasz write and would like to add:

1. If the relationtable is the correct way to go depends on some knowledge not contained in the table. It sounds strange that one medicine can be part of different groups and that the dosage depends on that relation. I would expect that a medicine can belong to different groups (resulting in a medicine2group mapping table) and that their exist different dosages depending on the age for a medicine (so you get dosage4age table, combining the existing age and dose tables. That new table would directly reference the medicine)

Which version is correct can not be told from the table alone.

As a rule of thumb: I get skeptical when a table without a proper name and concept links more then two other table. It is possible but often hints at concept hiding somewhere.

In order to check if the proposed model is correct, ask the business experts if the table is still correct if you replace Antibiotika with Superantibiotika in one of the first three rows. If it is, this means that the dosage does not depend on the group and should not be linked to it, so the model proposed by me would be more correct.

If the altered table is not correct, your model might be the better one, but I would listen carefully about the explanation why it isn't correct.