Question

folks! I need some help with organizing database for application and I have no idea how to do it. Suppose following:
There is a list of academic subjects. For each subject we need to have a list of academic groups, which attend this subject. Then, for each group we need to have a list of dates. And for each date we need to have a list of students, and whether this student was present that day or not.
I have ugly data structures in my mind, will appreciate any help.

UPDATE

How do I see it:

Table1(the first col is date and second is list student’s id, who were present)

10/10/11 | id1, id2, id3

10/11/11 | id1, 1d3, id5

Table2:

subject1 | id1 id2 id3

subject2 | id3 id2

And again, ids are id of groups. Dont know how to connect those tables.

Answer 1

There are many considerations to balance when designing a database, but based on the information you provided so far, something like this might be a good start:

This ER model uses a lot identifying relationships (i.e. “migrating” parent’s primary key into child’s PK) and results in natural primary keys, as opposed to non-identifying relationships that would require usage of surrogate keys. A lot of people like surrogate keys these days, but the truth is that both design strategies have pros and cons. In particular:

• Natural keys are bigger (they “accumulate” fields over multiple levels of parent-child relationships).
• But also, natural keys require less JOINing.
• Natural keys can enforce constraints better in some special cases (such as diamond-shaped dependencies).