Question

For a database assignment I have to model a system for a school. Part of the requirements is to model information for staff, students and parents.

In the UML class diagram I have modelled this as those three classes being subtypes of a person type. This is because they will all require information on, among other things, address data.

My question is: how do I model this in the database (mysql)?

Thoughts so far are as follows:

1. Create a monolithic person table that contains all the information for each type and will have lots of null values depending on what type is being stored. (I doubt this would go down well with the lecturer unless I argued the case very convincingly).
2. A person table with three foreign keys which reference the subtypes but two of which will be null – in fact I’m not even sure if that makes sense or is possible?

3. According to this wikipage about django it’s possible to implement the primary key on the subtypes as follows:

   'id' integer NOT NULL PRIMARY KEY REFERENCES 'supertype' ('id')

4. Something else I’ve not thought of…

So for those who have modelled inheritance in a database before; how did you do it? What method do you recommend and why?

Links to articles/blog posts or previous questions are more than welcome.

Thanks for your time!

UPDATE

Alright thanks for the answers everyone. I already had a separate address table so that’s not an issue.

Cheers,

Adam

Answer 1

4 tables staff, students, parents and person for the generic stuff. Staff, students and parents have forign keys that each refer back to Person (not the other way around).

Person has field that identifies what the subclass of this person is (i.e. staff, student or parent).

EDIT:

As pointed out by HLGM, addresses should exist in a seperate table, as any person may have multiple addresses. (However – I’m about to disagree with myself – you may wish to deliberately constrain addresses to one per person, limiting the choices for mailing lists etc).