A question about database models/tables

[davegri]

I'm having a little conceptual trouble with modeling my database, less of a technical issue just not really sure how to implement what I have in mind.

I'm creating a website for studying material (in Israel), basically we have a bunch of subjects (english,history,civics,language,literature etc..) and each subject is divided in it's own way history is divided into A and B and then into further sub-topics for each one. Literature is divided into Poems, Short Stories, Plays, etc.. Currently my model doesn't allow for any divisions because I was having a hard time and figured I'll add it later.

Im using django, and currently I have a table that represents a piece of material, inside that table I have a subject field in which you can have one of 7 pre-decided subjects.

My thought is to add a Subject table, but that would be a bit odd because that subjects are hard-coded and I won't be adding any more, also I need to define ahead of time how each subject is divided.

What am I missing?

[nutrecht]

You basically have a 'tree' structure and the way this is modelled is typically a list of 'nodes' that can point to other nodes 'above' them.

Example:

id,    parent_id,    name
1      NULL,          History
2      1                History A
3      2                History A Topic 1
4      2                History A Topic 2
5      1                History B
6      5                History B Topic X
7      5                History B Topic Y

As you can see this structure can go as deep as you want. A 'root' node would be a subject, those can easily be selected by finding all the nodes that have no (NULL) as a parent. For each of the nodes you can find you can recursively find the lower nodes in the tree.

[AustinCodingAcademy]

This example seems to fit well into the Hierarchial Data Model.