Hi gang:
To further the Garbage Collection thread on to another level (i.e.,
preserving history) please consider this:
Okay, let's say we have a table containing all the instances of
tutors teaching courses. A record might look like this:
Course-to-Tutor table
course_id = 123
tutor_id = 7
date_active = 2/4/9
date_inactive = null
The above record was assembled from the following recrods:
Tutor table:
id = 7
name = joe
Course table:
id = 123
title = Introduction to Moonshine
Okay, so let's now delete the course "Introduction to Moonshine"!
At the first opportunity to search the Course-to-Tutor table we find
that the course 123 is now absent from our database and as such we
set the date_inactive field -- it won't be considered again.
Okay, so what does that tell us about the history? It only provides
that at one time joe taught an undefined course. Furthermore, if joe
quits, then we only have a record that says someone with an id of 7
taught a course with an id of 123 -- that doesn't make much sense,
does it?
Now, if we reconsider the Course-to-Tutor table and instead of
putting in the tutor_id and course_id, we put in the actual name of
the tutor and title of the class, then at least we have a history
that makes sense.
However by doing that, we violate the primary principle of a
relational database by creating redundant data.
I guess that one can say that if we never actually delete the tutor
nor the course, but instead just make them inactive as well, then we
have solved the problem -- is that the answer?
In any event, what problems do you foresee if I used the actual names
and titles for the Course-to-Tutor table instead of their id's? After
all, the instance records would retain a simple history of what
happened regardless of deletions AND a search for "Introduction to
Moonshine" should be essentially as fast as a search for "123" if
both fields are indexed, am I right or wrong?
Cheers,
tedd
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